[0001] The present invention relates to a glow plug.
[0002] In recent years, in order to cope with stricter exhaust gas regulations on diesel
engines, glow plugs have been required to provide higher heating-up temperature. In
order to provide higher heating-up temperature, a glow plug in which a heat generation
element containing tungsten (W) as a main component is disposed in a tubular member
(tube) is proposed (see
WO2014/206847).
[0003] In the case of the glow plug of
WO2014/206847, thermal performance may vary among individual glow plugs. Such variation occurs
because tungsten (W) used as a main component of a heat generation element is large
in resistance ratio (the ratio of the resistance of the heat generation element at
1,000°C to the resistance of the heat generation element at 20°C). If the resistance
of the heat generation element at room temperature varies among individual glow plugs,
the resistance of the heat generation element when energized varies more greatly among
individual glow plugs, and consequently, thermal performance may vary among individual
glow plugs.
[0004] Incidentally, in the case of the glow plug of
WO2014/206847, the heat generation element is inserted into a fusion zone at the forward end of
a tubular member and is joined to the tubular member through the fusion zone. At that
time, if the amount of the material of the heat generation element inserted into the
fusion zone varies among individual glow plugs, the resistance of the heat generation
element at room temperature may vary among individual glow plugs. In particular, in
manufacture of the glow plug, the forward end of the tubular member is melted and
then solidified to thereby fix the heat generation element in the fusion zone. At
that time, if the amount of the melted material of the tubular member varies, the
amount of insertion of the heat generation element into the fusion zone may vary among
individual glow plugs.
[0005] The present invention has been conceived to solve the above problem and an object
of the present invention is to reduce variation in thermal performance among individual
glow plugs.
- (1) A mode of the present invention provides a glow plug comprising: a tubular member
whose forward end is closed with a fusion zone, and a coiled heat generation element
disposed in the tubular member and containing W as a main component. A forward end
portion of the heat generation element is inserted into the fusion zone to thereby
be joined to the tubular member. In a cross section of the glow plug taken along an
axial line of the glow plug, with a cross section which is a rearmost one of cross
sections of the heat generation element appearing in the fusion zone on one side of
the axial line and which is disposed at least partially within the fusion zone being
defined as a first heat-generation-element cross section, with a forwardmost one of
cross sections of the heat generation element appearing externally of the fusion zone
on the one side of the axial line being defined as a second heat-generation-element
cross section, and with a cross section which is one of the cross sections of the
heat generation element appearing externally of the fusion zone on the one side of
the axial line and which is located immediately rearward of the second heat-generation-element
cross section being defined as a third heat-generation-element cross section, a distance
A in the direction of the axial line between a rearmost end of the first heat-generation-element
cross section and a forwardmost end of the second heat-generation-element cross section
is greater than a distance B in the direction of the axial line between a rearmost
end of the second heat-generation-element cross section and a forwardmost end of the
third heat-generation-element cross section.
According to the mode of the present invention, the distance A is rendered greater
than the distance B. Namely, the distance A (i.e., space) between the first heat-generation-element
cross section and the second heat-generation-element cross section is increased such
that the rear end surface of the fusion zone is disposed in the space. Accordingly,
even when, for example, the amount of the melted material of the tubular member varies
and thus the position of the rear end surface of the fusion zone varies some extent
in the axial direction, the rear end surface of the fusion zone can be positioned
in the inter-turn space between the first heat-generation-element cross section and
the second heat-generation-element cross section without fail. Thus, only a predetermined
amount of the material of the heat generation element at the forward end thereof can
be reliably inserted into the fusion zone, whereby variation in the resistance of
the heat generation element at room temperature among individual glow plugs can be
suppressed. Accordingly, variation in thermal performance among individual glow plugs
can be reduced.
Notably, the "first heat-generation-element cross section" may be disposed at least
partially within the fusion zone. Specifically, the entire first heat-generation-element
cross section may be disposed within the fusion zone; alternatively, a portion of
the first heat-generation-element cross section may be disposed within the fusion
zone.
- (2) The glow plug according to section (1) may be configured such that the distance
A and the distance B satisfy a relational expression of 1.30≤A/B≤4.00.
When the above-described relational expression is satisfied, variation in the resistance
of the heat generation element at room temperature among individual glow plugs can
be suppressed while the heat-up performance of the glow plug is secured to a sufficient
degree.
- (3) The glow plug according to section (1) or (2) may be configured such that, in
the cross section of the glow plug, with a cross section which is one of the cross
sections of the heat generation element appearing in the fusion zone on the one side
of the axial line and which is located immediately forward of the first heat-generation-element
cross section being defined as a fourth heat-generation-element cross section, a distance
C in the direction of the axial line between a rearmost end of the fourth heat-generation-element
cross section and a forwardmost end of the first heat-generation-element cross section
(including the case where C = 0) is equal to or less than the distance B.
In this case, since the distance C between the fourth heat-generation-element cross
section and the first heat-generation-element cross section is rendered equal to or
less than the distance B, the wall thickness of the tubular member between the forward
end of the heat generation element and the surface of the tubular member can be rendered
sufficiently large. As a result, it is possible to prevent exposure of the heat generation
element, which would otherwise occur when the tubular member wears.
In this case, the glow plug can simultaneously achieve reduction of thermal performance
variation and improvement of durability.
Notably, the expression "C = 0" means that the axial position of the rearmost end
of the fourth heat-generation-element cross section is the same as that of the forwardmost
end of the first heat-generation-element cross section.
- (4) The glow plug according to section (1) or (2) may be configured such that, in
the cross section of the glow plug, with a cross section which is one of the cross
sections of the heat generation element appearing in the fusion zone on the one side
of the axial line and which is located immediately forward of the first heat-generation-element
cross section being defined as a fourth heat-generation-element cross section, a radially
outermost end of the fourth heat-generation-element cross section is located inward
of a radially innermost end of the first heat-generation-element cross section, and
a rearmost end of the fourth heat-generation-element cross section is located rearward
of a forwardmost end of the first heat-generation-element cross section.
[0006] In this case, since the rearmost end of the fourth heat-generation-element cross
section is located rearward of the forwardmost end of the first heat-generation-element
cross section, the wall thickness of the tubular member between the forward end of
the heat generation element and the surface of the tubular member can be rendered
sufficiently large. As a result, it is possible to prevent exposure of the heat generation
element, which would otherwise occur when the tubular member wears.
[0007] In this case, the glow plug can simultaneously achieve reduction of thermal performance
variation and improvement of durability.
[0008] The invention will be further described by way of non-limitative example with reference
to the accompanying drawings, in which:
FIG. 1 is a view showing a glow plug.
FIG. 2 is a sectional view showing the structure of a sheath heater in detail.
FIG. 3 is a sectional view showing a forward end portion of a sheath tube and its
periphery.
FIG. 4 is a flowchart showing a method of manufacturing the glow plug.
FIGS. 5(a) and 5(b) are explanatory views showing a welding process in step S20.
FIGS. 6(a) and 6(b) are explanatory views showing a welding process in step S20 of
another embodiment.
FIG. 7 is a sectional view showing a forward end portion of a sheath tube of still
another embodiment and its periphery.
1. Glow Plug
[0009] FIG. 1 shows a glow plug 10. The glow plug 10 includes a sheath heater (heat generation
device) 800 for generating heat and functions as a heat source for assisting ignition
at startup of an internal combustion engine (not shown) such as a diesel engine. The
glow plug 10 includes the sheath heater 800, an axial rod 200, and a metallic shell
500. These component members of the glow plug 10 are assembled together along the
axial direction OD of the glow plug 10. FIG. 1 shows an external structure on the
right side of an axial line O and a sectional structure on the left side of the axial
line O. In the present specification, a side toward the sheath heater 800 in the glow
plug 10 is called the "forward side," and a side toward an engagement member 100 is
called the "rear side."
[0010] The metallic shell 500 is a tubular member formed of carbon steel. The metallic shell
500 holds the sheath heater 800 at a forward end portion thereof. Also, the metallic
shell 500 holds the axial rod 200 at a rear end portion thereof through an insulation
member 410 and an O-ring 460. The position of the insulation member 410 along the
axial line O is fixed as a result of a ring 300 in contact with the rear end of the
insulation member 410 being crimped to the axial rod 200. Further, a portion of the
axial rod 200 extending from the insulation member 410 to the sheath heater 800 is
disposed in an axial hole 510 of the metallic shell 500. The axial hole 510 is a through
hole formed along the axial line O and is greater in diameter than the axial rod 200.
In a state in which the axial rod 200 is positioned in the axial hole 510, a gap is
formed between the axial rod 200 and the wall of the axial hole 510 for electrically
insulating them from each other. The sheath heater 800 is press-fitted into a forward
end portion of the axial hole 510 to thereby be joined to the forward end portion.
The metallic shell 500 further includes a tool engagement portion 520 and an external
thread portion 540. A tool (not shown) is engaged with the tool engagement portion
520 of the metallic shell 500 for attaching and detaching the glow plug 10. The external
thread portion 540 meshes with an internal thread formed in an internal combustion
engine (not shown).
[0011] The axial rod 200 is a circular columnar (rodlike) member formed of an electrically
conductive material. While being inserted through the axial hole 510 of the metallic
shell 500, the axial rod 200 is disposed in position along the axial line O. The axial
rod 200 includes a forward end portion 210 formed at the forward end side and an external
thread portion 290 provided at the rear end side. The forward end portion 210 is inserted
into the sheath heater 800. The external thread portion 290 protrudes rearward from
the metallic shell 500. The engagement member 100 meshes with the external thread
portion 290.
[0012] FIG. 2 is a sectional view showing the structure of a sheath heater 800 in detail.
With the forward end portion 210 of the axial rod 200 inserted into the sheath heater
800, the sheath heater 800 is press-fitted into the axial hole 510 of the metallic
shell 500 to thereby be joined to the metallic shell 500. The sheath heater 800 includes
a sheath tube 810, a heat generation coil 820, a rear coil 830, and an insulator 870.
The heat generation coil 820 is also called the "forward end coil." The heat generation
coil 820 corresponds to the coiled heat generation element of the present invention.
[0013] The sheath tube 810 is a tubular member extending in the axial direction OD and having
a closed forward end and corresponds to the tubular member of the present invention.
The sheath tube 810 accommodates therein the heat generation coil 820, the rear coil
830, and the insulator 870. The sheath tube 810 includes a side portion 814 extending
in the axial direction OD, a forward end portion 813 connected to the forward end
of the side portion 814 and curved outward, and a rear end portion 819 opening in
a direction opposite the forward end portion 813. The forward end portion 210 of the
axial rod 200 is inserted into the sheath tube 810 from the rear end portion 819.
The sheath tube 810 is electrically insulated from the axial rod 200 by a packing
600 and the insulator 870. Meanwhile, the sheath tube 810 is in contact with the metallic
shell 500 to thereby be electrically connected to the metallic shell 500. The sheath
tube 810 is formed of, for example, austenitic stainless steel which contains iron
(Fe), chromium (Cr), and carbon (C), or a nickel (Ni)-based alloy such as INCONEL
601 (INCONEL is a registered trademark) or Alloy602 (corresponding to DIN2.4633 alloy
specified by German Industrial Standard (DIN)).
[0014] The insulator 870 is formed of powder of an electrical insulation material. For example,
magnesium oxide (MgO) powder is used as the insulator 870. The insulator 870 is filled
into (disposed in) a gap which remains in the sheath tube 810 as a result of disposition
of the axial rod 200, the heat generation coil 820, and the rear coil 830 in the sheath
tube 810, thereby providing electrical insulation in the gap.
[0015] The heat generation coil 820 is disposed in the sheath tube 810 along the axial direction
OD and generates heat by energization thereof. The heat generation coil 820 includes
a forward end portion 822, which is a forward coil end portion, and a rear end portion
829, which is a rear coil end portion. The forward end portion 822 is located in the
forward end portion 813 of the sheath tube 810 and electrically connected to the sheath
tube 810. The rear end portion 829 is electrically connected to the rear coil 830
through a connection 840 formed as a result of welding of the heat generation coil
820 and the rear coil 830. The main component of the heat generation coil 820 is tungsten
(W). Notably, the main component is a substance whose content (% by mass) is 50% by
mass or higher. Preferably, the tungsten (W) content of the heat generation coil 820
is 99% by mass or higher.
[0016] No particular limitation is imposed on the wire diameter of the heat generation coil
820; however, the wire diameter is preferably 0.1 mm to 0.25 mm.
[0017] The rear coil 830 includes a forward end portion 831, which is a forward coil end
portion, and a rear end portion 839, which is a rear coil end portion. The forward
end portion 831 is welded to the rear end portion 829 of the heat generation coil
820 to thereby be electrically connected to the heat generation coil 820. The rear
end portion 839 is joined to the forward end portion 210 of the axial rod 200 to thereby
be electrically connected to the axial rod 200. The rear coil 830 is formed of, for
example, a nickel (Ni)-chromium (Cr) alloy or an iron (Fe)-chromium (Cr)-aluminum
(Al) alloy.
[0018] In view of securement of rapid heat-up performance, preferably, the resistance R
20 of the glow plug 10 at 20°C is 0.6 Ω or less. In the present embodiment, the resistance
R
20 of the glow plug 10 at 20°C is the sum of the resistance of the heat generation coil
820 at 20°C and the resistance of the rear coil 830 at 20°C. In the present embodiment,
the resistance R
20 of the glow plug 10 at 20°C is 0.4 Ω. In the present embodiment, a resistance ratio
R1 which is the ratio of the resistance R1
1000 of the heat generation coil 820 at 1,000°C to the resistance R1
20 of the heat generation coil 820 at 20°C and a resistance ratio R2 which is the ratio
of the resistance R2
1000 of the rear coil 830 at 1,000°C to the resistance R2
20 of the rear coil 830 at 20°C satisfy a relation of R1 > R2.
[0019] FIG. 3 is a sectional view showing the forward end portion 813 of the sheath tube
810 and its periphery. The forward end of the sheath tube 810 is closed with the fusion
zone 891.
[0020] FIG. 3 shows a cross section of the glow plug 10 taken along the axial line O of
the glow plug 10 such that the same number of cross sections of the heat generation
coil 820 appear in the fusion zone 891 on opposite sides of the axial line O. In FIG.
3, the right side of the axial line O is taken as one side of the axial line O, and
the left side is taken as the other side. In FIG. 3, two cross sections of the heat
generation coil 820 appear in the fusion zone 891 on each of opposite sides of the
axial line O. FIG. 3 shows the heat generation coil 820, the sheath tube 810, and
the insulator 870, which are cut along a plane passing through the axial line O.
[0021] The fusion zone 891 of the sheath tube 810 contains columnar crystals (dendrite),
whereas a base metal portion 893 other than the fusion zone 891 has a microstructure
different from that of the fusion zone 891. Examples of the microstructure of the
base metal portion 893 include a fibrous microstructure and a forged microstructure.
The microstructure can be identified as columnar crystals, a fibrous microstructure,
or a forged microstructure by a publicly known metal microstructure observation method;
specifically, by electrolytic etching of a cut surface in an oxalate solution (JIS
G 5071 2012), for example.
[0022] Forward n turns (n is a natural number) of the heat generation coil 820 are inserted
into the fusion zone 891. In the present embodiment, two turns of the heat generation
coil 820 at the forward end are inserted into the fusion zone 891.
[0023] As shown in FIG. 3, in the fusion zone 891, the first turn 901 and the second turn
902 appear in this order from the forward end side (lower side in the drawing) on
opposite sides of the axial line O.
[0024] In a region outside the fusion zone 891, the third turn 903 and the fourth turn 904
appear in this order from the forward end side (lower side in the drawing) on the
opposite sides of the axial line O.
[0025] The rearmost one of the cross sections of the heat generation coil 820 appearing
in the fusion zone 891 on one side of the axial line O will be referred to as a first
heat-generation-element cross section 902a. Also, a cross section which is one of
the cross sections of the heat generation coil 820 appearing in the fusion zone 891
on the one side of the axial line O and which is located immediately forward of the
first heat-generation-element cross section 902a will be referred to as a fourth heat-generation-element
cross section 901a. Also, the forwardmost one of the cross sections of the heat generation
coil 820 appearing externally of the fusion zone 891 on the one side of the axial
line O will be referred to as a second heat-generation-element cross section 903a.
Further, a cross section which is one of the cross sections of the heat generation
element 820 appearing externally of the fusion zone 891 on the one side of the axial
line O and which is located immediately rearward of the second heat-generation-element
cross section 903a will be referred to as a third heat-generation-element cross section
904a.
[0026] In the present invention, a distance A between the first heat-generation-element
cross section 902a and the second heat-generation-element cross section 903a is rendered
greater than a distance B between the second heat-generation-element cross section
903a and the third heat-generation-element cross section 904a.
[0027] No particular limitation is imposed on the distance A; however, the distance A is
preferably greater than 0.2 mm and not greater than 0.6 mm.
[0028] No particular limitation is imposed on the distance B; however, the distance B is
preferably not less than 0.1 mm and not greater than 0.2 mm.
[0029] The following actions and effects are yielded when the distance A is rendered greater
than the distance B.
[0030] According to one mode of the present invention, the distance A (i.e., space) between
the first heat-generation-element cross section 902a and the second heat-generation-element
cross section 903a is increased such that the rear end surface 895 of the fusion zone
891 is disposed in the space. Accordingly, even when the amount of the melted material
of the sheath tube 810 varies and thus the position of the rear end surface 895 of
the fusion zone 891 varies in the axial direction, the rear end surface 895 can be
positioned between the first heat-generation-element cross section 902a and the second
heat-generation-element cross section 903a without fail. Thus, only a predetermined
amount of the material of the heat generation coil 820 at the forward end thereof
can be reliably inserted into the fusion zone 891, whereby variation in the resistance
at room temperature among individual glow plugs can be suppressed. Accordingly, variation
in thermal performance among individual glow plugs can be reduced, and the heat generation
coil 820 can be prevented from coming off the sheath tube 810. Notably, the reason
why the above-described relation of the distances A and B reduces the variation in
thermal performance among individual glow plugs will be described in detail in the
after-mentioned section "Examples."
[0031] Further, in the present embodiment, preferably, the distance A and the distance B
satisfy the following relational expression.
[0032] When A/B is equal to or greater than 1.30, the variation in thermal performance among
individual glow plugs can be suppressed. When A/B is equal to or less than 4.00, the
glow plug 10 can have sufficiently high heat-up performance.
[0033] Further, in the present embodiment, desirably, a distance C between the fourth heat-generation-element
cross section 901a and the first heat-generation-element cross section 902a is equal
to or less than the distance B.
[0034] No particular limitation is imposed on the distance C between the fourth heat-generation-element
cross section 901a and the first heat-generation-element cross section 902a; however,
the distance C is preferably not less than 0 mm and not greater than 0.10 mm.
[0035] By setting the distance C to be equal to or less than the distance B, the wall thickness
of the sheath tube 810 between the forward end of the heat generation coil 820 and
the surface of the sheath tube 810 (thickness indicated by symbol D in FIG. 3) can
be rendered sufficiently large. As a result, it is possible to prevent exposure of
the coil 820 which would otherwise occur when the sheath tube 810 wears, whereby durability
can be improved.
[0036] Aglow plug 10 of another (second) embodiment (modification) will be described with
reference to FIG. 7. Notably, constituent members or portions of the glow plug 10
of the second embodiment which are approximately the same as those of the glow plug
10 of the above-described embodiment are denoted by like reference numerals, and description
of their structures, actions, and effects is omitted.
[0037] In the glow plug 10 of the second embodiment, as in the glow plug 10 of the above-described
embodiment, the radially outermost end 901aa of the fourth heat-generation-element
cross section 901a is located inward of the radially innermost end 902aa of the first
heat-generation-element cross section 902a.
[0038] The glow plug 10 of the second embodiment differs from the glow plug 10 of the above-described
embodiment in the following point.
[0039] Namely, the rearmost end 901ab of the fourth heat-generation-element cross section
901a is located rearward of the forwardmost end 902ab of the first heat-generation-element
cross section 902a. Namely, the fourth heat-generation-element cross section 901a
and the first heat-generation-element cross section 902a are disposed to overlap each
other in the axial direction OD. By virtue of this arrangement, the wall thickness
of the sheath tube 810 between the forward end of the heat generation coil 820 and
the surface of the sheath tube 810 (thickness indicated by symbol D in FIG. 7) can
be rendered sufficiently large. As a result, it is possible to prevent exposure of
the coil 820 which would otherwise occur when the sheath tube 810 wears, whereby durability
can be improved.
2. Method of Manufacturing Glow Plug 10
[0040] FIG. 4 is a flowchart showing a method of manufacturing the glow plug 10. In manufacture
of the glow plug 10, first, the heat generation coil 820 and the axial rod 200 are
welded together (step S10). Specifically, the heat generation coil 820 and the rear
coil 830 are welded together; further, the rear end portion 839 of the rear coil 830
and the forward end portion 210 of the axial rod 200 are welded together. Next, the
forward end portion 822 of the heat generation coil 820 and the forward end portion
813 of the sheath tube 810 are welded together (step S20). Step S20 is also called
the "welding process."
[0041] FIGS. 5(a) and 5(b) are explanatory views showing a welding process in step S20.
In the welding process, first, there is prepared a sheath tube 810P which includes
a forward end portion 813P having an opening 815 and which is shaped such that diameter
gradually reduces toward the opening 815. The forward end portion 822 of the heat
generation coil 820 is disposed inside the forward end portion 813P of the prepared
sheath tube 810P such that the second turn 822P of the heat generation coil 820 comes
into contact with the sheath tube 810P (FIG. 5(a)). Next, while the forward end portion
813P is melted by, for example, arc welding from outside and then is solidified to
close the opening 815, the forward end portion 822 of the heat generation coil 820
and the forward end portion 813 of the sheath tube 810 are welded together (FIG. 5(b)).
By this procedure, the forward end portion 822 of the heat generation coil 820 is
surrounded by and embedded in the forward end portion 813 of the sheath tube 810.
Also, in the welding process, output of the welding machine, welding time, etc. are
adjusted such that the heat generation coil 820 and the sheath tube 810 are welded
together at a temperature lower than the melting point of the heat generation coil
820 and higher than the melting point of the sheath tube 810.
[0042] Notably, in the case where an alloy of a metal used to form the sheath tube 810 and
a metal used to form the heat generation coil 820 is formed between the forward end
portion 813 of the sheath tube 810 and the forward end portion 822 of the heat generation
coil 820, the thickness of an alloy portion formed of the alloy is 10 (µm) or less.
The thickness of the alloy portion can be calculated by detecting the alloy portion
through analysis of a region in the vicinity of the boundary between the forward end
portion 822 of the heat generation coil 820 and the forward end portion 813 of the
sheath tube 810 by use of, for example, EPMA (Electron Probe Micro Analyzer). Notably,
in the glow plug 10 of the present embodiment, the alloy portion is not formed.
[0043] When the welding process in step S20 is completed, the insulator 870 is filled into
the sheath tube 810 (step S30). The insulator 870 covers the heat generation coil
820, the rear coil 830, and the axial rod 200 to thereby fill a gap formed in the
sheath tube 810, whereby assembly of the sheath heater 800 is completed.
[0044] After the completion of assembling of the sheath heater 800, swaging is performed
on the sheath heater 800 (step S40). Swaging is performed such that striking force
is applied to the sheath heater 800 to thereby reduce the diameter of the sheath heater
800, so as to densify the insulator 870 filled into the sheath tube 810. When striking
force is applied to the sheath heater 800 as a result of swaging, the striking force
is transmitted to the interior of the sheath heater 800, thereby densifying the insulator
870.
[0045] After swaging is performed on the sheath heater 800, the sheath heater 800 and the
metallic shell 500 are combined to thereby assemble the glow plug 10 (step S50), whereby
the glow plug 10 is completed. Specifically, the sheath heater 800 integrated with
the axial rod 200 is fixedly press-fitted into the axial hole 510 of the metallic
shell 500; the O-ring 460 and the insulation member 410 are fitted to the axial rod
200 at a rear end portion of the metallic shell 500; and the engagement member 100
is meshed with the external thread portion 290 of the axial rod 200 located rearward
of the rear end of the metallic shell 500. Also, in step S50, aging is performed on
the glow plug 10. Specifically, the assembled glow plug 10 is energized so that the
sheath heater 800 generates heat, thereby forming an oxide film on the outer surface
of the sheath heater 800.
[Examples]
[0046] The present invention will be described further in detail by way of example.
[0047] Notably, experimental examples 2 to 6 are examples of the present invention, and
experimental example 1 is a comparative example.
1. Preparation of Glow Plugs
[0048] In the glow plugs 10 of each experimental example, the forward end shape of the heat
generation coil 820 was adjusted so as to adjust the distance A, the distance B, and
the distance C. Other conditions are as follows:
- A tungsten material (wire diameter φ: 0.20 mm) was used to form the heat generation
coil 820.
- A nickel-chromium alloy material (wire diameter φ: 0.38 mm) was used to form the rear
coil 830.
- Resistance at room temperature was adjusted to 0.330 Ω.
- The sheath tube 810 had an outside diameter of 3.25 mm at a small-diameter portion
thereof.
- Each distance was measured as follows: each glow plug 10 after temperature measurement
was disassembled, and then the sheath heater 800 was cut along the axial line O of
the glow plug such that the same number of cross sections of the heat generation element
820 appeared in the fusion zone 891 on the opposite sides of the axial line O, and
the cut surface was used for for measurement.
[0049] The sheath heater 800 was cut such that the region where the forward end portion
831 of the rear coil 830 and the rear end portion 829 of the heat generation coil
820 are welled together appeared on the cut surface on the left side (on the other
side), and the clearances between the cross sections of the heat generation coil 820
were measured on the cut surface on the right side (on one side).
2. Performance Test
2.1 Variation in temperature
[0050] 20 glow plugs 10 were prepared for each experimental example. A rated voltage was
applied to each glow plug 10, and the temperature of the glow plugs 10 was measured
after elapse of 100 seconds. The value of 3σ was obtained for the temperatures of
the 20 glow plugs 10 for each experimental example and was evaluated as follows.
○ (good): The value of 3σ was less than 70°C
X (poor): The value of 3σ was equal to or greater than 70°C
[0051] The rated voltage was determined as follows. Namely, the voltage sensitivity of the
first glow plug for each experimental example was measured, the relation between voltage
and temperature was determined, and a voltage at which the temperature becomes 1,100°C
was used as the rated voltage.
[0052] Notably, the temperature was measured at a position located 2 mm from the forward
end of the sheath tube 810 by use of a PR thermocouple (platinum-platinum rhodium
thermocouple) and a radiation thermometer.
2.2 Durability
[0053] A voltage for increasing the glow plug temperature by 1,000°C in two seconds was
applied to each glow plug 10; then, a voltage for saturating the glow plug temperature
at 1,100°C was applied to each glow plug 10 continuously for 180 seconds. Subsequently,
each glow plug 10 was cooled by wind for 120 seconds for lowering the glow plug temperature
to room temperature. With this procedure taken as one cycle, a cycle test was conducted.
Each glow plug 10 was subjected to 7,000 test cycles. Each glow plug 10 was evaluated
on the basis of the results of the determination as to whether or not a wire breakage
occurred during the durability test.
○ (good): No wire breakage occurred even after 500 hours (about 6,000 cycles)
X (poor): Wire breakage occurred before 500 hours (about 6,000 cycles)
[0054] Notably, the temperature was measured at a position located 2 mm from the forward
end of the sheath tube 810 by use of a PR thermocouple (platinum-platinum rhodium
thermocouple) and a radiation thermometer.
2.3 Rapid heat-up performance
[0055] A voltage of 11 V was applied to each glow plug 10 for 2 seconds, and its temperature
after elapse of 2 seconds was measured. The temperature was measured at a position
located 2 mm from the forward end of the sheath tube 810 by use of a PR thermocouple
(platinum-platinum rhodium thermocouple) and a radiation thermometer. The rapid heat-up
performance was evaluated as follows.
○ (good): The temperature reached after elapse of 2 seconds was 900°C or higher
X (poor): The temperature reached after elapse of 2 seconds was lower than 900°C
3. Test Results
[0056] Table 1 shows the test results.
Table 1
Experimental example |
A (mm) |
B (mm) |
C (mm) |
A/B |
C/B |
Temp. variation |
Durability |
Rapid heat-up performance |
1 |
0.10 |
0.10 |
0.07 |
1.00 |
0.700 |
X |
X(1) |
○ |
2 |
0.13 |
0.10 |
0.07 |
1.30 |
0.700 |
○ |
○ |
○ |
3 |
0.40 |
0.10 |
0.07 |
4.00 |
0.700 |
○ |
○ |
○ |
4 |
0.45 |
0.10 |
0.07 |
4.50 |
0.700 |
○ |
○ |
X |
5 |
0.50 |
0.10 |
0.10 |
5.00 |
1.000 |
○ |
○ |
○ |
6 |
0.50 |
0.10 |
0.13 |
5.00 |
1.300 |
○ |
X(2) |
○ |
(1) The heat generation coil came off the sheath tube.
(2) The forward end of the heat generation coil was exposed from the forward end of
the sheath tube. |
[0057] In experimental examples 2 to 6, the value of 3σ (index of temperature variation)
was less than 70°C, and the temperature variation among the individual glow plugs
10 was small. Meanwhile, in experimental example 1, the value of 3σ (index of temperature
variation) was equal to or greater than 70°C, and the temperature variation was large.
Accordingly, it was confirmed that when the distance A is rendered greater than the
distance B, the variation in thermal performance among individual glow plugs can be
reduced.
[0058] Further, for experimental examples 2 and 3 which also meet the requirement that
the value of A/B is not less than 1.30 and not greater than 4.00, it was confirmed
that the variation in thermal performance among individual glow plugs can be suppressed,
and rapid heat-up performance can be secured to a sufficient degree.
[0059] Also, in the case of experimental examples 2 to 5 which also meet the requirement
that the distance C between the first turn and the second turn is equal to or less
than the distance B, even after about 6,000 cycles, the forward end of the heat generation
coil was not exposed from the forward end of the sheath tube. Thus, it was confirmed
that when the distance C is equal to or less than the distance B, durability is excellent.
<Other Embodiments (Modifications)>
[0060] The present invention is not limited to the above embodiments and examples, but may
be embodied in various other forms without departing from the gist of the invention.
- (1) In the above-described embodiments, as shown in FIG. 5(a), the glow plug 10 is
manufactured by use of the sheath tube 810P having the opening 815; however, as shown
in FIG. 6(a), the glow plug 10 may be manufactured by use of a sheath tube 810R having
no opening. In FIGS. 6(a) and 6(b), constituent members or portions approximately
the same as those of the glow plugs of the above embodiments are denoted by like reference
numerals, and description of their structures, actions, and effects is omitted.
- (2) In the above-described embodiments, two turns of the heat generation coil 820
at the forward end thereof are inserted into the fusion zone 891. However, the number
of turns inserted into the fusion zone 891 is not limited to two. For example, one
to five turns of the heat generation coil 820 at the forward end thereof may be inserted
into the fusion zone 891.
[Description of Reference Numerals]
[0061]
- 10:
- glow plug
- 100:
- engagement member
- 200:
- axial rod
- 210:
- forward end portion
- 290:
- external thread portion
- 300:
- ring
- 410:
- insulation member
- 460:
- O-ring
- 500:
- metallic shell
- 510:
- axial hole
- 520:
- tool engagement portion
- 540:
- external thread portion
- 600:
- packing
- 601:
- INCONEL
- 800:
- sheath heater
- 810:
- sheath tube
- 813:
- forward end portion
- 814:
- side portion
- 815:
- opening
- 819:
- rear end portion
- 820:
- heat generation coil
- 822:
- forward end portion
- 829:
- rear end portion
- 830:
- rear coil
- 831:
- forward end portion
- 839:
- rear end portion
- 840:
- connection
- 870:
- insulator
- 890:
- fusion zone
- 891:
- fusion zone
- 893:
- base metal portion
- 901:
- first turn
- 902:
- second turn
- 903:
- third turn
- 904:
- fourth turn
1. Glühkerze (10), umfassend:
ein rohrförmiges Element (810), dessen vorderes Ende mit einer Schmelzzone (891) verschlossen
ist, und
ein gewickeltes Wärmeerzeugungselement (820), das im rohrförmigen Element (810) angeordnet
ist und W als eine Hauptkomponente enthält,
wobei ein vorderer Endabschnitt des Wärmeerzeugungselements (820) in die Schmelzzone
(891) eingeschoben wird, um dadurch mit dem rohrförmigen Element (810) verbunden zu
werden; und
in einem Querschnitt der Glühkerze (10) entlang einer Axiallinie (O) der Glühkerze
(10),
mit einem Querschnitt, der ein hinterster von Querschnitten des Wärmeerzeugungselements
(820) ist, die in der Schmelzzone (891) auf einer Seite der Axiallinie (O) auftreten
und der mindestens teilweise innerhalb der Schmelzzone (891) angeordnet ist, definiert
als ein erster Wärmeerzeugungselement-Querschnitt (902a),
mit einem vordersten der Querschnitte des Wärmeerzeugungselements (820), die außerhalb
der Schmelzzone (891) auf der einen Seite der Axiallinie (O) auftreten, definiert
als zweiter Wärmeerzeugungselement-Querschnitt (903a), und
mit einem Querschnitt, der einer der Querschnitte des Wärmeerzeugungselements (820)
ist, die außerhalb der Schmelzzone (891) auf der einen Seite der Axiallinie (O) auftreten
und der unmittelbar hinter dem zweiten Wärmeerzeugungselement-Querschnitt (903a) liegt,
definiert als ein dritter Wärmeerzeugungselement-Querschnitt (904a),
dadurch gekennzeichnet, dass
ein Abstand A in Richtung der Axiallinie (O) zwischen einem hintersten Ende des ersten
Wärmeerzeugungselement-Querschnitts (902a) und einem vordersten Ende des zweiten Wärmeerzeugungselement-Querschnitts
(903a) größer ist als ein Abstand B in Richtung der Axiallinie (O) zwischen einem
hintersten Ende des zweiten Wärmeerzeugungselement-Querschnitts (903a) und einem vordersten
Ende des dritten Wärmeerzeugungselement-Querschnitts (904a).
2. Glühkerze nach Anspruch 1, wobei der Abstand A und der Abstand B einen Vergleichsausdruck
von 1,30≤A/B≤4,00 erfüllen.
3. Glühkerze nach Anspruch 1 oder 2, wobei
im Querschnitt der Glühkerze (10),
mit einem Querschnitt, der einer der Querschnitte des Wärmeerzeugungselements (820)
ist, die in der Schmelzzone (891) auf der einen Seite der Axiallinie (O) auftreten,
und der unmittelbar vor dem ersten Wärmeerzeugungselement-Querschnitt (902a) liegt,
definiert als ein vierter Wärmeerzeugungselement-Querschnitt (901a),
ein Abstand C in Richtung der Axiallinie (O) zwischen einem hintersten Ende des vierten
Wärmeerzeugungselement-Querschnitts (901a) und einem vordersten Ende des ersten Wärmeerzeugungselement-Querschnitts
(902a) (einschließlich des Falls, in dem C = 0) gleich oder kleiner als der Abstand
B ist.
4. Glühkerze nach Anspruch 1 oder 2, wobei
im Querschnitt der Glühkerze (10),
mit einem Querschnitt, der einer der Querschnitte des Wärmeerzeugungselements (820)
ist, die in der Schmelzzone (891) auf der einen Seite der Axiallinie (O) auftreten
und der unmittelbar vor dem ersten Wärmeerzeugungselement-Querschnitt (902a) angeordnet
ist, definiert als ein vierter Wärmeerzeugungselement-Querschnitt (901a),
ein radial äußerstes Ende des vierten Wärmeerzeugungselement-Querschnitts (901a) nach
innen von einem radial innersten Ende des ersten Wärmeerzeugungselement-Querschnitts
(902a) liegt, und
ein hinterstes Ende des vierten Wärmeerzeugungselement-Querschnitts (901a) hinter
einem vordersten Ende des ersten Wärmeerzeugungselement-Querschnitts (902a) liegt.