JP7037338B2 - Glow plug - Google Patents

Description

The present invention relates to a glow plug used as a starting aid for an internal combustion engine such as a diesel engine.

Ceramic heater type glow plugs are known as glow plugs used to assist the starting of diesel engines. Such a ceramic heater type glow plug includes a ceramic heater and an outer cylinder that houses a part of the ceramic heater so that at least the tip is exposed.

The outer cylinder has a base end having a relatively small outer diameter on the tip side in the axial direction of the glow plug and a base end having a larger outer diameter than the outer diameter of the tip portion integrally continuous with the rear end of the tip in the axial direction. Has a part.

The ceramic heater is exposed from the tip of the outer cylinder and also from the rear end of the outer cylinder when it is inserted into the outer cylinder, and is supported at the base end of the outer cylinder via a joint such as brazing. Has been done. The ceramic heater has a U-shaped heat generating portion and two leads connected to both rear ends of the heat generating portion in a substantially cylindrical insulating ceramic. One of the two leads has an exposed portion exposed to the outside from the outer peripheral surface of the insulating ceramic, and the exposed portion is electrically connected to the inner peripheral surface of the outer cylinder via the joint portion. (See, for example, Patent Document 1).

Further, a glow plug that supports a ceramic heater at the tip of an outer cylinder having a tip and a base end via a joint is known (see, for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2013-76513 Japanese Unexamined Patent Publication No. 2011-7372

By the way, as in Patent Document 1, in the glow plug in which the ceramic heater protrudes from the tip of the outer cylinder along the axial direction and also protrudes from the rear end, it is necessary to configure the ceramic heater for a long time. The cost was high.

On the other hand, as in Patent Document 2, the length of the ceramic heater is shortened, and the ceramic heater is joined to the tip of the outer cylinder via the joint portion to suppress the extended length of the ceramic heater. When trying to reduce the manufacturing cost, the exposed part is located closer to the heat generating part, so that the exposed part of the lead becomes hot and the heat load on the joint part that joins the exposed part and the outer cylinder increases. It will be.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to suppress a heat load on a joint portion that joins an exposed portion of a lead and an outer cylinder in a ceramic heater.

In order to achieve the above object, the glow plug according to the present invention includes a ceramic heater and an outer cylinder that accommodates a part of the ceramic heater so that at least the tip of the ceramic heater is exposed. Has a tubular tip portion that is joined to the ceramic heater via the joint portion and a tubular base end portion that is connected to the rear end of the tip portion, and the outer peripheral surface of the base end portion is , Which is flush with the outer peripheral surface of the tip portion, or is located outside the outer peripheral surface of the tip portion with respect to the central axis of the outer cylinder, and the inner peripheral surface of the base end portion is the center. It is characterized in that it is located inside the inner peripheral surface of the tip portion with respect to the axis line.

Further, the outer cylinder is formed in a cylindrical shape, the outer diameter of the tip portion is _DA , the outer diameter of the base end portion is _{DB, the inner diameter of the tip portion is d A ,} and the base end portion. When the inner diameter of is _dB , it is preferable that _DA ≤ _DB and d _A > _dB .

Further, the ceramic heater has a conductive ceramic and an insulating ceramic covering the conductive ceramic, and the conductive ceramic has a heat generating portion and a lead connected to the rear end of the heat generating portion. The lead has a positive electrode side lead and a negative electrode side lead, and the negative electrode side lead has a rear end exposed from the outer peripheral surface of the insulating ceramic and is electrically charged to the inner peripheral surface of the tip end portion of the outer cylinder. It is good that they are connected to each other.

Further, a cylindrical housing for supporting the base end portion of the outer cylinder is further provided, and the base end portion is a cylinder for supporting the base end portion of the outer cylinder whose tip is at least partially protruding from the housing. The base end portion may further include a shaped housing, the tip of which may at least partially project from the housing.

According to the present invention, in the ceramic heater, the heat load on the joint portion where the exposed portion of the lead and the outer cylinder are joined is suppressed.

It is sectional drawing along the axis of the glow plug which concerns on this embodiment in the state of being attached to a cylinder head. It is a schematic diagram for demonstrating the structure of the outer cylinder of the glow plug which concerns on this embodiment.

A preferred embodiment of the present invention will be described with reference to the drawings. It should be noted that the embodiment shown below is an example, and various embodiments can be taken within the scope of the present invention. FIG. 1 is a cross-sectional view taken along the axis of the glow plug according to the present embodiment in a state of being attached to the cylinder head. FIG. 2 is a schematic diagram for explaining the configuration of the outer cylinder of the glow plug according to the present embodiment.

The glow plug 1 is, for example, a ceramic heater type glow plug, and as shown in FIG. 1, includes a ceramic heater 10, a metal outer cylinder 20 accommodating a part of the ceramic heater, and a housing 30. There is.

The ceramic heater 10 assists in starting the internal combustion engine, and is inside the combustion chamber Cc (pre-combustion chamber in the case of a pre-combustion type internal combustion engine, and combustion chamber of the internal combustion engine in the case of a direct injection type internal combustion engine). ), And fixed to the housing 30 via the outer cylinder 20. The ceramic heater 10 is made of ceramics.

The ceramic heater 10 has a conductive ceramic 11 and an insulating ceramic 16 that covers the conductive ceramic 11. The ceramic heater 10 is a rod-shaped member having a dome-shaped tip.

The conductive ceramics 11 are heated by energization in the glow plug 1, and the U-shaped heat generating portion 12 arranged at the tip thereof and the lead 14 connected to the rear end of the heat generating portion 12 are connected to each other. Have.

The heat generating portion 12 is a heat generating resistor having high resistance to the lead 14, and is formed of conductive ceramics. The heat generating portion 12 has a pair of extending portions 12a and 12b extending in parallel with each other along the axis x of the ceramic heater 10, and a curved portion 12c connecting the extending portions 12a and 12b. The shape of the heat generating portion 12 is not particularly limited in the cross-sectional view perpendicular to the axis x direction, and various shapes such as a circle, an ellipse, an oval, and a polygon can be taken. The "axis line x" is a line passing through the center of gravity in the cross section of the ceramic heater 10.

The heat generating portion 12 is formed of, for example, a material containing a carbide containing tungsten (W), molybdenum (Mo), titanium (Ti), a nitride, a silice, or the like as a main component. It is particularly preferable that the heat generating portion 12 contains tungsten carbide (WC) having high heat resistance and inorganic conductivity in that the specific resistance is small.

The heat generating portion 12 contains silicon nitride (Si ₃ N ₄ ) in addition to the above-mentioned main component, and the content of silicon nitride (Si ₃ N ₄ ) is preferably 20% by mass or more. For example, the conductor component serving as the heat generating portion 12 has a larger thermal expansion rate than silicon nitride (Si ₃ N ₄ ) in the insulating ceramics 16 including the silicon nitride ceramics, and therefore is usually in a state where tensile stress is applied. It is in. On the other hand, by adding silicon nitride (Si _{3N 4 )} to the heat generating portion 12, the thermal expansion rate is brought closer to the thermal expansion rate of the insulating ceramics 16, and the temperature of the ceramic heater 10 is raised and lowered. It is possible to relieve the stress due to the difference in the thermal expansion rate of.

Further, when the content of silicon nitride (Si ₃ N ₄ ) contained in the heat generating portion 12 is 40% by mass or less, the resistance value of the heat generating portion 12 can be made relatively small and stabilized. Therefore, the content of silicon nitride (Si ₃ N ₄ ) contained in the heat generating portion 12 is preferably 20 to 40% by mass. More preferably, the content of silicon nitride (Si ₃ N ₄ ) is 25 to 35% by mass.

As a similar additive to the heat generating portion 12, _{4 to 12% by mass of boron nitride (BN) may be added instead of silicon nitride (Si 3N 4 )} . Further, the heat generating portion 12 includes elements of groups 4, 5, 6, 7, and 8 (titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), and iron (Mn) in the 4th period of the Periodic Table of the Elements. It may contain at least one of Fe)).

For example, the content of the elements of titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), and iron (Fe) in the heat generating portion 12 is preferably 0.5 mol% or less.

The lead 14 is connected to the heat generating portion 12 on one end side and is exposed from the insulating ceramic 16 on the other end side. The lead 14 has a positive electrode side lead 14a and a negative electrode side lead 14b. The shape of the lead 14 is not particularly limited in the cross-sectional view perpendicular to the axis x direction, and various shapes such as a circle, an ellipse, an oval, and a polygon can be taken.

The positive electrode side lead 14a and the negative electrode side lead 14b are each formed of conductive ceramics having low resistance to the heat generating portion 12. The positive electrode side lead 14a and the negative electrode side lead 14b extend in parallel with each other along the axis x direction of the ceramic heater 10. The positive electrode side lead 14a and the negative electrode side lead 14b are the extending portions 12 of the heat generating portion 12 extending in a U shape.
It is connected to the rear end of each of a and 12b.

The positive electrode side lead 14a is connected to the extending portion 12a of the heat generating portion 12. The positive electrode side lead 14a extends inside the insulating ceramic 16 to the rear end of the insulating ceramic 16. At the rear end of the ceramic heater 10, the positive electrode side lead 14a is exposed from the insulating ceramic 16 and is electrically connected to the lead wire 115 via the cap-shaped connecting portion 114.

The rear end of the negative electrode side lead 14b is exposed from the outer peripheral surface of the insulating ceramics 16 and is electrically connected to the inner peripheral surface of the tip portion 22 of the outer cylinder 20. The negative electrode side lead 14b has an exposed portion 14c whose tip is connected to the extending portion 12b of the heat generating portion 12 and whose rear end is partially exposed from the insulating ceramics 16 to the outer peripheral surface.

The exposed portion 14c of the lead 14 is joined to the inner peripheral surface of the outer cylinder 20 by brazing or the like via a joining portion 21 described later. It is electrically connected to an outer cylinder 20 formed of a conductive metal material. The exposed portion 14c of the negative electrode side lead 14b functions as a negative electrode side electrode.

The lead 14 contains tungsten carbide (WC), which is an inorganic conductor, as a main component, and it is preferable to add silicon nitride (Si _{3N 4 )} to the lead 14 so that the content is 15% by mass or more. As the content of silicon nitride (Si ₃ N ₄ ) increases, the thermal expansion coefficient of the positive lead side lead 14a and the negative electrode side lead 14b becomes closer to the thermal expansion coefficient of silicon nitride (Si ₃ N ₄ ) contained in the insulating ceramics 16. be able to.

When the content of silicon nitride is 40% by mass or less, the resistance values of the positive electrode side lead 14a and the negative electrode side lead 14b become small and stable. Therefore, the content of silicon nitride (Si ₃ N ₄ ) is preferably 15 to 40% by mass. More preferably, the content of silicon nitride (Si ₃ N ₄ ) is preferably 20 to 35% by mass.

Further, the lead 14 has elements of groups 4, 5, 6, 7, and 8 (titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), and iron (Fe) in the 4th period of the Periodic Table of the Elements. )) At least one kind of oxide and / or nitride may be contained. For example, the content of the elements of titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), and iron (Fe) in the lead 14 is preferably 0.5 mol% or less.

The lead 14 is preferably a mixture containing, for example, a rare earth element compound such as chromium oxide (Cr _{2O 3} ) of about several tens of PPM, and is a sintered body formed by sintering.

The lead 14 is made of the same material as the heat generating portion 12, but is more than the heat generating portion 12, for example, by containing more forming material than the heat generating portion 12 or by making the cross-sectional area larger than that of the heat generating portion 12. The resistance value per unit length is low.

The insulating ceramic 16 is, for example, a sintered body having a cylindrical outer peripheral surface formed by sintering. The insulating ceramic 16 covers the conductive ceramic 11, and more specifically, the insulating ceramic 16 covers the heat generating portion 12 and the lead 14. In other words, the heat generating portion 12 and the lead 14 are embedded in the insulating ceramics 16.

Since the insulating ceramics 16 are made of ceramics, it is possible to provide a highly reliable ceramic heater 10 at the time of rapid temperature rise. Specific examples thereof include ceramics having electrical insulating properties such as oxide ceramics, nitride ceramics, and carbide ceramics.

In particular, silicon nitride ceramics, which is the main component of silicon nitride ceramics, is excellent in terms of high strength, high toughness, high insulation and heat resistance. This silicon dioxide ceramic has, for example, yttrium oxide (Y ₂ O ₃ ), ytterbium oxide (Yb ₂ O ₃ ), and erybium oxide (Yb 2 O 3) in an amount of 3 to 12% by mass as a sintering aid with respect to silicon dioxide as a main component. The amount of rare earth element oxides such as Er _{2O 3} ), 0.5 to 3% by mass of aluminum oxide (Al2O3), and silicon dioxide (SiO ₂ ) contained in the sintered body is 1.5 to 5% by mass. It is obtained by mixing silicon dioxide (SiO ₂ ) as described above and hot-press firing.

When a silicon nitride ceramic is used as the insulating ceramic 16, it is preferable to mix and disperse molybdenum dissilicate (MoSi ₂ ), tungsten disilicate (WSi ₂ ) and the like. In this case, the thermal expansion rate of the silicon nitride ceramics as the base material can be brought close to the thermal expansion rate of the heat generating portion 12, and the durability of the ceramic heater 10 can be improved.

As shown in FIG. 2, the outer cylinder 20 is formed of, for example, stainless steel such as SUS430 having a cylindrical shape. The outer cylinder 20 accommodates the ceramic heater 10 in a state where the tip portion of the ceramic heater 10 is exposed.

The outer cylinder 20 is located on the tip side (combustion chamber Cc side) in the x-direction of the axis, and has a cylindrical tip portion 22 for accommodating the ceramic heater 10 of the glow plug 1 so that at least the tip is exposed, and a cylinder head Ch. A tubular base end portion 23 connected to the rear end of the tip end portion 22 supported by the housing 30 to be attached is provided.

The outer peripheral surface of the base end portion 23 of the outer cylinder 20 is located outside the outer peripheral surface of the tip end portion 22 with respect to the axis x, and the inner peripheral surface of the base end portion 23 is the tip portion 22 with respect to the axis line x. It is located inside the inner peripheral surface. In the outer cylinder 20 of the present embodiment, the outer diameter of the tip portion 22 is _DA , the outer diameter of the base end portion 23 is _{DB, the inner diameter of the tip portion 22 is d A ,} and the inner diameter of the base end portion 23 is d. When _B is set, _DA < _DB and d _A > _dB are satisfied.

That is, in the outer cylinder 20, the outer diameter _DA of the tip portion 22 is smaller than the outer diameter _DB of the base end portion 23, but the inner diameter d _A of the tip portion 22 is smaller than the inner diameter _dB of the base end portion 23. big. The wall thickness (wall thickness) of the base end portion 23 with respect to the tip end portion 22 is large. Specifically, the outer peripheral surface of the base end portion 23 is located outward in the radial direction with respect to the outer peripheral surface of the tip end portion 22. Since the inner peripheral surface is located inward in the radial direction with respect to the inner peripheral surface of the tip portion 22, the wall thickness of the base end portion 23 is larger than the wall thickness of the tip portion 22. ..

In the present embodiment, the outer diameter _DA of the tip portion 22 and the outer diameter DB of the base end portion 23 have a relationship of _{DA < DB} , but the relationship is not limited to this, and the tip portion is not limited to this relationship. The outer diameter _DA of 22 and the outer diameter DB of the base end portion 23 may be the same ( _{DA = DB} ). In this case, in the outer cylinder 20, _DA = _{DB and d A > dB} .

A tapered portion 24 having a diameter increasing from the tip end portion 22 side to the proximal end portion 23 side is formed between the tip end portion 22 and the proximal end portion 23, and the tapered portion 24 is formed at the proximal end portion 24. It is included in the part 23.

In the state where the ceramic heater 10 is housed, the ceramic heater 10 and the outer cylinder 20 are placed on the inner peripheral surface of the tip portion 22 of the outer cylinder 20 at a predetermined length along the axis x of the ceramic heater 10, for example, silver brazing. A joint portion 21 to be joined by brazing using a brazing material such as the above is formed. The exposed portion 14c of the negative electrode side lead 14b exposed from the outer peripheral surface of the insulating ceramic 16 is electrically connected to the inner peripheral surface of the tip portion 22 of the outer cylinder 20 via the joint portion 21.

The joint portion 21 is formed by metallizing the outer peripheral surface of the insulating ceramic 16 by brazing a brazing material such as silver brazing, and is formed by metallizing the outer peripheral surface of the ceramic heater 10 by a predetermined length along the axis x of the ceramic heater 10. It is formed between the surface and the inner peripheral surface of the outer cylinder 20. In the present embodiment, the joint portion 21 is formed from the tip of the outer cylinder 20 to a position where the insulating ceramic 16 is in contact with the inner peripheral surface of the tip portion 22 of the outer cylinder 20 on the rear end side. However, the tip of the joint portion 21 may extend from the outer cylinder 20 on the axis x, or may be inside the outer cylinder 20.

The housing 30 is a mounting tool for the cylinder head Ch of the engine, and accommodates the ceramic heater 10 together with the outer cylinder 20. The housing 30 is made of a thermally conductive metal material having excellent heat dissipation. The housing 30 is formed in a cylindrical shape, for example, and supports the base end portion 23 of the outer cylinder 20 so that the tip end portion of the base end portion 23 of the outer cylinder 20 projects at least partially.

According to the glow plug 1 as described above, since the ceramic heater 10 is housed so that the tip of the ceramic heater 10 is exposed at the tip 22 of the outer cylinder 20, for example, the conventional ceramic supported at the base end. Compared with the heater, the length in the axis x direction can be shortened, and the manufacturing cost of the ceramic heater 10 can be suppressed.

Further, the outer diameter _{DA of the tip portion 22 of the outer cylinder 20 of the ceramic heater 10 and the outer diameter DB of the base end portion 23 satisfy DA <DB, and the inner diameter d A and the base end} of the tip portion 22 are satisfied. Since the inner diameter _dB of the portion 23 satisfies d _A > _dB , it is possible to secure a large path in the base end portion 23 for discharging the heat generated in the ceramic heater 10 and transmitted through the tip portion 22.

In the glow plug 1, since the ceramic heater 10 is supported by the tip portion 22 of the outer cylinder 20, the position where the exposed portion 14c of the negative electrode side lead 14b comes into contact with the tip portion 22 via the joint portion 21 is the base end. It is closer to the heat generating portion 12 than in the case where the ceramic heater 10 is supported in the portion 23. However, since the exhaust heat path is largely secured at the base end portion 23, the heat load at the joint portion 21 in contact with the exposed portion 14c can be reduced, and thus the long-term life of the joint portion 21 is achieved. can do.

Further, the wall thickness at the base end portion 23 is not only to increase the outer diameter _DB with respect to the outer diameter _DA of the tip portion 22, but also to decrease the inner diameter _{dB with respect to the inner diameter d A of} the tip end portion 22. It is larger than the wall thickness of the tip portion 22. As a result, it is possible to prevent only the outer diameter _DB of the base end portion 23 from becoming large, and the outer cylinder 20 can contribute to saving the installation space thereof.

Further, since it is possible to suppress the expansion of the outer diameter _DB at the base end portion 23, the base end portion 23 partially protrudes from the housing 30 without contacting the inner peripheral surface of the glow hole Gh of the cylinder head Ch. Can be made to. As a result, the amount of protrusion of the base end portion 23 from the housing 30 can be adjusted relatively freely, and the amount of protrusion of the glow plug 1 into the combustion chamber Cc without changing the length of the ceramic heater 10 itself. Can be adjusted.

<Others>
The present invention is not limited to the above-described embodiment, and can be appropriately modified without exceeding the scope of the present invention. For example, the outer peripheral surface of the ceramic heater 10 is formed in a cylindrical shape in the present embodiment, but may have various different cross-sectional shapes such as a polygon such as an ellipse or a rectangle.

When the cross section of the outer cylinder 20 is not limited to a cylinder but is formed into a rectangular shape, for example, the outer peripheral surface of the base end portion 23 of the outer cylinder 20 is flush with the outer peripheral surface of the tip portion 22. It is located outside the outer peripheral surface of the tip portion 22 with respect to the central axis of the outer cylinder 20, and the inner peripheral surface of the base end portion 23 is located inside the inner peripheral surface of the tip portion 22 with respect to the central axis. It should be. Here, the "central axis of the outer cylinder 20" is a line passing through the centroid in the cross section of the outer cylinder 20.

In other words, the outer peripheral length of the tip portion 22 is _{LA, the outer peripheral length of the base end portion 23 is LB, the inner peripheral length of the tip portion 22 is l A , and} the inner peripheral length of the base end portion 23 is l. When _B is set, _LA ≤ _{LB and l A >} l _B are satisfied.

1 Glow plug 10 Ceramic heater 11 Conductive ceramics 12 Heat generating part 14 Lead 14a Positive electrode side lead 14b Negative electrode side lead 14c Exposed part 16 Insulating ceramics 20 Outer cylinder 21 Joint part 22 Tip part 23 Base end part 30 Housing _DA Tip Outer diameter d _A Inner diameter of the tip D _B Outer diameter of the base end d _B Inner diameter of the base end x Axis line

Claims (3)

With a ceramic heater
An outer cylinder accommodating a part of the ceramic heater so that at least the tip of the ceramic heater is exposed,
Equipped with
The outer cylinder is
A cylindrical tip that is joined to the ceramic heater via the joint,
A cylindrical base end connected to the rear end of the tip and
Have,
The outer peripheral surface of the base end portion is flush with the outer peripheral surface of the tip portion, or is located outside the outer peripheral surface of the tip portion with respect to the central axis of the outer cylinder.
The inner peripheral surface of the base end portion is located inside the inner peripheral surface of the tip end portion with respect to the central axis .
A cylindrical housing that supports the base end of the outer cylinder is further provided.
The base end portion has a tip that at least partially protrudes from the housing.
A glow plug that features that. The outer cylinder is formed in a cylindrical shape and has a cylindrical shape.
The outer diameter of the tip is _DA , and the outer diameter of the base is _DB .
When the inner diameter of the tip is d _A and the inner diameter of the base is _dB .
_DA ≤ _{DB and d A > dB}
The glow plug according to claim 1, wherein the glow plug meets the requirements. The ceramic heater has a conductive ceramic and an insulating ceramic that covers the conductive ceramic.
The conductive ceramic has a heat generating portion and a lead connected to the rear end of the heat generating portion.
The lead has a positive electrode side lead and a negative electrode side lead.
The negative electrode side lead according to claim 1 or 2, wherein the rear end is exposed from the outer peripheral surface of the insulating ceramic and is electrically connected to the inner peripheral surface of the tip end portion of the outer cylinder. Glow plug.

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