U.S. patent application number 10/004841 was filed with the patent office on 2002-08-29 for glow plug.
This patent application is currently assigned to NGK SPARK PLUG CO., LTD.. Invention is credited to Kimata, Hiroyuki, Teramura, Hideki.
Application Number | 20020117492 10/004841 |
Document ID | / |
Family ID | 18857776 |
Filed Date | 2002-08-29 |
United States Patent
Application |
20020117492 |
Kind Code |
A1 |
Teramura, Hideki ; et
al. |
August 29, 2002 |
GLOW PLUG
Abstract
A glow plug includes an inner pole and a ceramic heating rod
disposed in and fixed to an outer shell at uppermost and lowermost
pole fixed portions A, C and a heating rod fixed portion D. A ratio
of L2/L1 is larger than 2, where L1 is a distance from the lower
end of the inner pole to the lower end of the fixed portion C; and
L2 is a distance from the lower end of the inner pole to the lower
end of the fixed portion A. A ratio of L3/L4 is smaller than 15,
wherein L3 is a distance from a middle point between the lower end
of the inner pole and the upper end of the heating rod to the lower
end of the fixed portion C; and L4 is a distance from the above
middle point to the upper end of the fixed portion D.
Inventors: |
Teramura, Hideki; (Mie,
JP) ; Kimata, Hiroyuki; (Aichi, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037-3202
US
|
Assignee: |
NGK SPARK PLUG CO., LTD.
|
Family ID: |
18857776 |
Appl. No.: |
10/004841 |
Filed: |
December 7, 2001 |
Current U.S.
Class: |
219/270 ;
123/145A |
Current CPC
Class: |
F23Q 7/001 20130101 |
Class at
Publication: |
219/270 ;
123/145.00A |
International
Class: |
F23Q 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2000 |
JP |
2000-391671 |
Claims
What is claimed is:
1. A glow plug comprising: an outer shell; an inner pole disposed
partly in the outer shell and fixed thereto at a plurality of pole
fixed portions, the inner pole having first and second ends, the
pole fixed portions including first and second pole fixed portions
located nearest to the first and second ends of the inner pole,
respectively, each of the first and second pole fixed portions
having first and second ends located nearer to the first and second
ends of the inner pole, respectively; a ceramic heating rod
disposed partly in the outer shell in line with the inner pole, the
ceramic heating rod having first and second ends, the second end of
the ceramic heating rod being located adjacent to the first end of
the inner pole; and an electric conductor electrically connecting
the inner pole with the ceramic heating rod, wherein a ratio of
L2/L1 is larger than 2, where L1 is a distance from the first end
of the inner pole to first end of the first pole fixed portion and
L2 is a distance from the first end of the inner pole to the first
end of the second pole fixed portion.
2. The glow plug according to claim 1, wherein the ratio of L2/L1
is equal to or larger than 2.5.
3. The glow plug according to claim 1, having a length of equal to
or greater than 8 cm from the second end of the inner pole to the
first end of the ceramic heating rod.
4. The glow plug according to claim 3, having a length of equal to
or greater than 10 cm from the second end of the inner pole to the
first end of the ceramic heating rod.
5. The glow plug according to claim 4, having a length of equal to
or greater than 15 cm from the second end of the inner pole to the
first end of the ceramic heating rod.
6. A glow plug comprising: an outer shell; an inner pole
disposed-partly in the outer shell and fixed thereto at one or more
pole fixed portions, the inner pole having first and second ends,
the one or more pole fixed portions including a first pole fixed
portion located nearest to the first end of the inner pole, the
first pole fixed portion having first and second ends located
nearer to the first and second ends of the inner pole,
respectively; a ceramic heating rod disposed partly in the outer
shell in line with the inner pole and fixed thereto at one or more
heating rod fixed portions, the ceramic heating rod having first
and second ends, the second end of the ceramic heating rod being
located adjacent to the first end of the inner pole, the one or
more heating rod fixed portions including a first heating rod fixed
portion located nearest to the second end of the ceramic heating
rod, the first heating rod fixed portion having first and second
ends located nearer to the first and second ends of the ceramic
heating rod, respectively; and an electric conductor electrically
connecting the inner pole with the ceramic heating rod, wherein a
ratio of L3/L4 is smaller than 15, where L3 is a distance from a
middle point between the first end of the inner pole and the second
end of the ceramic heating rod to the first end of the first pole
fixed portion and L4 is a distance from the middle point to the
second end of the first heating rod fixed portion.
7. The glow plug according to claim 6, wherein the one or more pole
fixed portions further includes a second pole fixed portion located
nearest to the second end of the inner pole, the second pole fixed
portion having first and second ends located nearer to the first
and second ends of the inner pole, respectively, and a ratio of
L2/L1 is larger than 2, where L1 is a distance from the first end
of the inner pole to the first end of the first pole fixed portion
and L2 is a distance from the first end of the inner pole to the
first end of the second pole fixed portion.
8. The glow plug according to claim 6, wherein the ratio of L3/L4
is equal to or smaller than 10.
9. The glow plug according to claim 8, wherein the ratio of L3/L4
is within a range from 1 to 6.
10. The glow plug according to claim 9, wherein the ratio of L3/L4
is within a range from 4 to 6.
11. The glow plug according to claim 7, wherein the ratio of L2/L1
is equal to or larger than 2.5.
12. The glow plug according to claim 6, having a length of equal to
or greater than 8 cm from the second end of the inner pole and the
first end of the ceramic heating rod.
13. The glow plug according to claim 12, having a length of equal
to or greater than 10 cm from the second end of the inner pole and
the first end of the ceramic heating rod.
14. The glow plug according to claim 13, having a length of equal
to or greater than 15 cm from the second end of the inner pole and
the first end of the ceramic heating rod.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a glow plug, and more
specifically a glow plug that is highly resistant to shocks and
vibrations even when it is longer than conventional. The present
invention further relates to a glow plug suitable for a direct
injection diesel engine.
[0002] For pollution control, a direct injection diesel engine has
recently come into use. In some cases, the direct injection diesel
engine requires a glow plug longer than conventional.
SUMMARY OF THE INVENTION
[0003] The glow plug is inevitably subjected to shocks and
vibrations transmitted thereto from the engine over a long period
of usage, and at the same time, is caused to resonate by the shocks
and vibrations. Accordingly, in such a longer glow plug, it is
highly likely that a ceramic member is cracked and/or an electric
conductor that connects a ceramic heater with an inner pole is
broken under the influence of the shocks, vibrations and
resonance.
[0004] It is therefore an object of the present invention to
provide a glow plug that attains excellent durability over a longer
period of usage, when it has a length similar to a conventional
glow plug.
[0005] It is also an object of the present invention to provide a
glow plug that is highly resistant to shocks and vibrations, even
when it has a greater length than a conventional glow plug.
[0006] According to one aspect of the invention, there is provided
a glow plug comprising: an outer shell; an inner pole disposed
partly in the outer shell and fixed thereto at a plurality of pole
fixed portions, the inner pole having first and second ends, the
pole fixed portions including first and second pole fixed portions
located nearest to the first and second ends of the inner pole,
respectively, each of the first and second pole fixed portions
having first and second ends located nearer to the first and second
ends of the inner pole, respectively; a ceramic heating rod
disposed partly in the outer shell in line with the inner pole, the
ceramic heating rod having first and second ends, the second end of
the ceramic heating rod being located adjacent to the first end of
the inner pole; and an electric conductor electrically connecting
the inner pole with the ceramic heating rod, wherein a ratio of
L2/L1 is larger than 2, where L1 is a distance from the first end
of the inner pole to first end of the first pole fixed portion and
L2 is a distance from the first end of the inner pole to the first
end of the second pole fixed portion.
[0007] According to another aspect of the invention, there is
provided a glow plug comprising: an outer shell; an inner pole
disposed partly in the outer shell and fixed thereto at one or more
pole fixed portions, the inner pole having first and second ends,
the one or more pole fixed portions including a first pole fixed
portion located nearest to the first end of the inner pole, the
first pole fixed portion having first and second ends located
nearer to the first and second ends of the inner pole,
respectively; a ceramic heating rod partly disposed in the outer
shell in line with the inner pole and fixed thereto at one or more
heating rod fixed portions, the ceramic heating rod having first
end and second ends, the second end of the ceramic heating rod
being located adjacent to the first end of the inner pole, the one
or more heating rod fixed portions including a first heating rod
fixed portion located nearest to the second end of the ceramic
heating rod, the first heating rod fixed portion having first and
second ends located nearer to the first and second ends of the
ceramic heating rod, respectively; and an electric conductor
electrically connecting the inner pole with the ceramic heating
rod, wherein a ratio of L3/L4 is smaller than 15, where L3 is a
distance from a middle point between the first end of the inner
pole and the second end of the ceramic heating rod to the first end
of the first pole fixed portion and L4 is a distance from the
middle point to the second end of the first heating rod fixed
portion.
BRIEF DESCRIPTION OF THE DRAWING
[0008] FIG. 1 is a sectional view of a glow plug G according to a
preferred embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0009] A glow plug G according to one embodiment of the invention
will be explained below with reference to FIG. 1. Herein, the terms
"upper" and "lower" are used to indicate positions when the glow
plug G is observed in the orientation of FIG. 1.
[0010] As shown in FIG. 1, the glow plug G includes a metallic
outer shell 2, an inner pole 1, a ceramic heating rod 3 and coiled
electric conductors 41, 42.
[0011] The outer shell 2 is formed into a cylindrical shape so that
the inner pole 1 and the ceramic heating rod 3 are disposed partly
within the outer shell 2 and in line with each other. Although the
outer shell 2 is formed of a single piece in the present embodiment
as shown in FIG. 1, it can be formed of some separate sections
(including, e.g., a section for covering the inner pole 1 and a
section for covering the ceramic heating rod 3).
[0012] A threaded portion 22 is formed on the outer shell 2, and is
adapted to attach the glow plug G to a cylinder head (not shown in
the drawing). A tool engaging portion 23 is also formed on the
outer shell 2 to be engaged with a tool (not shown) for fitting the
glow plug G in the cylinder head.
[0013] The inner pole 1 has a terminal rod 11 made of, e.g., low
carbon steel and a metallic inner shell 12 made of, e.g., SUS304
(stainless steel according to JIS). The terminal rod 11 is
coaxially retained in the inner shell 12. A space between the
terminal rod 11 and the inner shell 12 is filled with a filling
material 13 of, e.g., magnesia powder. At the time of filling with
the filling material 13, one end of the inner shell 12 is closed up
with a rubber plug (not shown). Then, the filling material 13 is
compressed by swaging the inner shell 12 from its outside to
inside, before the rubber plug is removed. It is therefore possible
to attain a high mechanical strength of the terminal rod 11. It is
also possible to assemble the inner pole 1 easily, being
electrically insulated from the outer shell 2.
[0014] The ceramic heating rod 3 includes a heating resistor 31,
lead wires 321, 322 and a ceramic body 32. The heating resistor 31
and the lead wires 321, 322 are disposed in the ceramic body 32, as
shown in FIG. 1. The heating resistor 31 is formed into a U-like
shape. One end portion of each lead wire 321, 322 is connected to
the heating resistor 31, while the other end portion is exposed at
the surface of the ceramic body 32. The ceramic heating rod 3
further includes a protective shell 21 that covers the ceramic body
32. The protective shell 21 is brazed to the ceramic body 32 by
filling a space between the ceramic body 32 and the protective
shell 21 with a brazing filler, while heated. The ceramic body 32
protrudes from the lower end of the protective shell 21 by some
distance (e.g., by a distance of 9 mm), upon shrinkage of the
protective shell 21 and the brazing filler, when cooled.
[0015] The electric conductor 41 is fit onto the ceramic body 32,
and is brazed so as to establish an electrical connection between
the lead wire 321 and the protective shell 21 through the electric
conductor 41. One end portion of the electric conductor 42 is fit
on and brazed to the ceramic body 32, while the other end portion
is fit on and welded to the inner pole 1, thereby establishing an
electrical connection between the lead wire 322 and the inner pole
1 through the electric conductor 42.
[0016] The inner pole 1 and the ceramic heating rod 3, attached to
each other as described above, are disposed in and fixed to the
outer shell 2 at a plurality of fixed portions. As used herein, the
term "fix" is intended to mean to prevent movement of the inner
pole 1 and the ceramic heating rod 3 relative to the outer shell 2.
The number of the fixed portions is not specifically limited. The
length of each fixed portion is not limited either.
[0017] The fixing of the inner pole 1 and the ceramic heating rod 3
to the outer shell 2 can be carried out according to any
conceivable method. In other words, the inner pole 1 and the
ceramic heating rod 3 may be directly fixed to the outer shell 2
by, e.g., caulking. Alternatively, the inner pole 1 and the ceramic
heating rod 3 may be fixed to the outer shell 2 by, e.g., press
fitting, shrinkage fitting or swaging with a fixing material, such
as an insulation ring, a glass sealing material, a heat resisting
resin and a powder filler.
[0018] For example, the inner pole 1 and the ceramic heating rod 3
can be fixed to the outer shell 2 at four fixed portions A to D, as
shown in FIG. 1. At the fixed portion D, an upper end portion of
the protective tube 21 may be brazed to a lower end portion of the
outer shell 2. The protective shell 21 thus gets in the outer shell
2 by some distance (e.g., by a distance of 8 mm). The outer shell 2
may be caulked at each of the fixed portions B and C. A sealing
material 5 of, e.g., glass powder may be packed in a space between
the inner pole 1 and the outer shell 2, and then, dissolved and
solidified at the fixed portion A.
[0019] A nut 7 is screwed onto the inner pole 1, while an
insulating member 6 is interposed between the inner pole 1 and the
nut 7.
[0020] Accordingly, when a voltage is applied to the glow plug G,
the voltage is supplied to the heating resistor 31 through the
inner pole 1, the electric conductor 42 and the lead wire 322.
Also, the heating resistor 31 is grounded through the lead wire
321, the electric conductor 41, the protective shell 21 and the
outer shell 2 to an engine block (not shown in the drawing). The
heating resistor 31 thus generates heat through electrical
resistance.
[0021] Herein, for explanation purposes, distances L1 to L4 are
defined as follows.
[0022] L1: A distance from the lower end of the inner pole 1 to the
lower end of the lowermost fixed portion at which the inner pole 1
is fixed to the outer shell 2 (e.g., the fixed portion C in FIG.
1).
[0023] L2: A distance from the lower end of the inner pole 1 to the
lower end of the uppermost fixed portion at which the inner pole 1
is fixed to the outer shell 2 (e.g., the fixed portion A in FIG.
1).
[0024] L3: A distance from the middle point between the lower end
of the inner pole 1 and the upper end of the ceramic heating rod 3
to the lower end of the lowermost fixed portion at which the inner
pole 1 is fixed to the outer shell 2 (e.g., the fixed portion C in
FIG. 1).
[0025] L4: A distance from the middle point between the lower end
of the inner pole 1 and the upper end of the ceramic heating rod 3
to the upper end of the uppermost fixed portion at which the
ceramic heating rod 3 is fixed to the outer shell 2 (e.g., the
fixed portion D in FIG.
[0026] According to the invention, the inner pole 1 and the ceramic
heating rod 3 are fixed to the outer shell 2 so that a ratio of
L2/L1 is adjusted to be larger than 2; preferably equal to or
larger than 2.5, and/or so that a ratio of L3/L4 is adjusted to be
smaller than 15; preferably equal to or smaller than 10; more
preferably within a range from 1 to 6; and still more preferably
within a range from 1 to 4. When the ratio of L2/L1 is equal to or
smaller than 2, the glow plug G cannot attain sufficiently high
shock and vibration resistance. The glow plug G cannot attain
sufficiently high shock and vibration resistance either, when the
ratio of L3/L4 is equal to or larger than 15. The glow plug G can
attain especially high shock and vibration resistance, when the
inner pole 1 and the ceramic heating rod 3 are fixed to the outer
shell 2 in both of the above-described ratios of L2/L1, L3/L4.
[0027] Further, it is especially advantageous that the inner pole 1
and the ceramic heating rod 3 are fixed to the outer shell 2 in at
least one of the above-described ratios of L2/L1, L3/L4 in order to
attain high shock and vibration resistance of the glow plug G, when
the glow plug G has a length of not less than 8 cm (normally not
greater than 20 cm); particularly not less than 10 cm; and more
particularly not less than 15 cm, from the upper end of the inner
pole 1 to the lower end of the ceramic heating rod 3.
[0028] In the case where the glow plug G is installed on an
internal combustion engine, such as a direct injection diesel
engine, the glow plug G is subjected to vibrations transmitted
thereto from the engine in operation. Resonance occurs, if the glow
plug G has a resonance frequency similar to the frequency of such
vibrations (normally 20 to 1000 Hz). However, the glow plug G can
gain a resonance frequency of not less than 2000 Hz (normally not
greater than 5000 Hz); and preferably not less than 2500 Hz, at the
lower end portion of the inner pole 1, when the inner pole 1 and
the ceramic heating rod 3 are fixed to the outer shell 2 in the
above-described ratios of L2/L1, L3/L4. It is therefore possible to
highly improve the vibration resistance of the glow plug G by
avoiding such resonance.
[0029] The invention will be specifically illustrated in more
detail by way of the following experiments.
[0030] [Experiment 1]
[0031] A variety of glow plugs G1 to G12 were manufactured
according to the above-described embodiment with different ratios
of L2/L1, L3/L4 as listed in TABLE 1. In each glow plug, the inner
pole 1 and the ceramic heating rod 3 were fixed to the outer shell
2 by brazing at the fixed portion D, by caulking over 5 mm at each
of the fixed portions B and C, and then, by glass sealing at the
fixed portion A, as shown in FIG. 1. The ceramic body 32 protruded
from the lower end of the protective shell 21 by 9 mm, while the
protective shell 21 got in the outer shell 21 by 8 mm. The terminal
rod 11 was made of low carbon steel, the inner shell 12 was made of
SUS304, and the filling material 13 was of magnesia powder.
[0032] Then, the glow plugs G1 to G12 were tested for their shock
and vibration resistance, respectively.
[0033] According to the vibration testing method for automobile
parts of JIS D 1601 (1995) as indicated at JIS D 5103 (1992),
vibration tests were conducted with a vibration number of
1.0.times.10.sup.7, a frequency of 20 to 2000 Hz and an
acceleration of 25 G.
[0034] The test results are indicated in TABLE 1. Herein, five
samples were used for each glow plug for determining its vibration
resistance. The vibration resistance was marked "A", when all of
the samples (i.e., five samples) were energized to the end. The
vibration resistance was marked "B", when four samples were
energized to the end, but one sample ended up unable to be
energized in process of the test. When all of the samples became
unable to be energized in midstream, the vibration resistance was
marked "C".
[0035] According to the method of JIS B 8031 (1995) (although it is
intended for spark plugs for internal combustion engines), shock
tests were conducted with a stroke of 5 mm and a test time of 10
minutes. The test results are indicated in TABLE 1. The shock
resistance was determined in the same manner as the vibration
resistance.
[0036] As apparent from TABLE 1, the glow plugs G4 to G6 attained
high shock and vibration resistance with the respective ratios of
L2/L1 larger than 2 (particularly equal to or larger than 2.5).
Similarly, the glow plugs G7 to G10 attained high shock and
vibration resistance with the respective ratios of L3/L4 smaller
than 15 (particularly equal to or smaller than 10). Each of the
glow plugs G4 to G7 consistently attained excellent shock and
vibration resistance, when the ratio of L2/L1 was larger than 2,
and at the same time, the ratio of L3/L4 was smaller than 15.
[0037] [Experiment 2]
[0038] A glow plug G13 was further manufactured in the same manner
as the glow plug G4, except that the inner pole 1 was not fixed to
the outer shell 2 at the fixed portion C. That is, the ratios of
L2/L1, L3/L4 were 2.5 and 2, respectively in the glow plug G4. On
the other hand, the ratios of L2/L1, L3/L4 are not greater than 2
and not smaller than 15, respectively, in the glow plug G13.
[0039] The resonance frequencies of the glow plugs G4 and G13 were
measured at the respective lower end portions of the inner poles 1
as below.
[0040] In each glow plug, a hole of 3 mm in diameter was formed in
the lower end portion of the inner pole 1. Then, each glow plug was
screwed into and fixed to the equivalent of a cylinder head. The
resonance frequency was measured from the hole, while giving an
impact by a blow to the equivalent.
[0041] The glow plug G4 had a resonance frequency of 2500 Hz,
whereas the glow plug G13 had a resonance frequency of 1000 Hz. In
other words, the resonance frequency of the glow plug G4 was much
higher than the frequency (normally of 20 to 1000 Hz) of vibrations
transmitted from an internal combustion engine, such as a direct
injection diesel engine. It is therefore considered that resonance
would be hardly able to occur to the glow plug G4 even where the
glow plug G4 is installed on the internal combustion engine.
[0042] As described above, a glow plug according to the invention
is highly resistant to shocks and vibrations. Particularly, a glow
plug according to the invention can attain high shock and vibration
resistance, even when it has a greater length than a conventional
glow plug. Thus, the glow plug of the invention may be suitably
used in a direct injection diesel engine.
[0043] Although the invention has been described with reference to
a specific embodiment of the invention, the invention is not
limited to the above-described embodiment. Modification and
variation of the embodiment described above will occur to those
skilled in the art in light of the above teaching. For example, the
inner pole 1 may be comprised of the terminal rod 11 only, without
the inner shell 12 and the filling material 13. The electric
conductors 41, 42 may be of another type i.e., of rod type. The
scope of the invention is defined with reference to the following
claims.
1TABLE 1 Vibration Shock Glow Plug L2/L1 L3/L4 Resistance
Resistance Comparative G1 1 2 C C Example G2 1.5 B C G3 2 A B
Invention G4 2.5 A A G5 3 A A G6 3.5 A A G7 2.5 0.5 A A G8 1 A A G9
5 A A G10 10 A A Comparative G11 15 B A Example G12 20 C B
* * * * *