JP2002228153A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a thermal stress generated at a step part between a large diameter part and a small diameter part of a heat-generating element in a glow plug in which the heat-generating element is provided with the large diameter part and the small diameter part for reducing a size of the diameter at the extremity end. SOLUTION: There is provided a glow plug comprising a cylindrical housing 10 capable of being fixed to an engine; a cylindrical sleeve 20 of which one end 21 protrudes from one end 11 of the housing 10 and the other end 22 is inserted into and held at the housing 10; and a ceramic rod-like heat generating member 30 in which one end 31 protrudes from one end 21 of the sleeve 20, the other end 32 is inserted into and held at the sleeve 20 to generate heat through an electrical energization. The heat-generating member 30 is constructed such that the step part 36 is set at the midway segment, one end 31 is the small diameter part 37 and the other end 32 is the large diameter part 38, and the entire large diameter part 38 is arranged within the sleeve 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow plug provided with a large diameter portion and a small diameter portion on a heating element so as to reduce the diameter of a distal end portion.

[0002]

2. Description of the Related Art Generally, a glow plug of this type is held in a housing by inserting a cylindrical housing attachable to an engine, one end of the glow plug protruding from one end of the housing and the other end of the glow plug into the housing. And a ceramic rod-shaped heating element held by the sleeve by inserting the other end into the sleeve with one end protruding from one end of the sleeve. here,
Each insertion part is fixed by press fitting, brazing, or the like.

[0003] The glow plug is inserted into a mounting hole (glow hole) for the engine so that the protruding heating element faces the combustion chamber, and is fixed by screw connection or the like. Then, by energizing the heating element, the heating element generates heat, and the heat ignites the fuel in the combustion chamber. Thus, ignition and combustion of fuel at the time of starting the engine are promoted.

[0004]

In recent years, with the direct injection of diesel engines, glow plugs have tended to be longer and smaller due to restrictions on the engine side. It is becoming necessary to further reduce the diameter. For this reason, it is necessary to further reduce the diameter of the heating element, which is the tip (the end located on the combustion chamber side) of the glow plug.

[0005] In this case, it is optimal to make the whole of the heating element protruding from one end of the housing thinner, but there is a concern that strength may be reduced due to sticking of carbon or the like. For example, if carbon adheres to the glow hole, engine vibration is directly applied to the glow plug via the adhered carbon,
If the heating element is thin, cracks may occur or break.

[0006] For this reason, it is common practice to reduce the diameter of only the tip of the heating element. In other words, the heating element has a step portion in the middle thereof, and the tip portion has a small diameter portion and the opposite side has a large diameter portion.

However, in the case of a heating element having a stepped portion as described above, heat stress due to heat generated when the heating element is energized or the like tends to concentrate on the stepped portion, and the heating element is damaged from the stepped portion. Great fear.

In view of the above problems, the present invention provides a glow plug having a heating element having a large diameter portion and a small diameter portion in order to reduce the diameter of the tip portion. An object of the present invention is to make it possible to reduce the thermal stress generated in a steel sheet.

[0009]

According to the present inventors, in the conventional glow plug, the stepped portion of the heating element is exposed away from the sleeve, and the stepped portion has insufficient heat dissipation. It is thought that large thermal stress is likely to be generated. The present invention has been made by paying attention to improving the heat drawing property of a step portion of a heating element.

That is, according to the first aspect of the present invention, a cylindrical housing (10) attachable to an engine, one end (21) protrudes from one end (11) of the housing, and the other end (22) is protruded from the housing. A cylindrical sleeve (20) held in the housing by being inserted into the housing (20)
A glow having a ceramic rod-shaped heating element (30) that is held in the sleeve by being inserted into the sleeve while the other end (32) is inserted into the sleeve with one end (31) protruding from one end of the sleeve, and that generates heat when energized. In the plug, the heating element has a step portion (36) in the middle thereof, one end of which has a small diameter portion (37) and the other end has a large diameter portion (38), and all of the large diameter portion are sleeved. It is characterized by being arranged inside.

According to this, in the heating element, by arranging all of the large diameter portion in the sleeve, at least a part of the step portion comes into contact with the sleeve, and the step portion easily radiates heat through the sleeve. . Therefore, according to the present invention, the heat drawing property of the step portion is improved, and the thermal stress of the step portion can be reduced.

Here, as in the second aspect of the present invention,
By arranging all of the steps (36) in the sleeve (20), the effects of the first aspect can be realized at a higher level.

According to the third aspect of the present invention, the heating element (30) is made of a conductive ceramic.
And a lead wire (34) that is electrically connected to the heat-generating portion and energizes the heat-generating portion. The heat-generating portion and the lead wire are embedded in an insulator (35) made of insulating ceramic. If it is the case, the connecting portion between the heat generating portion and the lead wire is located at the large diameter portion (38) and the sleeve (20)
It is preferred to be located within.

Thus, the thermal stress generated at the connecting portion between the heat generating portion and the lead wire can be reduced, and the damage of the connecting portion due to the thermal stress can be suppressed.

The height of the step (36) can be 0.05 mm or more.

Further, it is preferable in terms of strength that the step portion (36) has an R shape or a tapered shape as in the invention described in claim 5.

Further, the diameter of the small diameter portion (37) is D1, the diameter of the large diameter portion (38) is D2, and so on.
Assuming that the length of the small diameter portion including the step portion (36) is L1, these dimensions D1, D2 and L1 may satisfy the relationship expressed by the following expression 2 with the unit of mm. Thus, it is possible to provide a glow plug that is strong against vibration applied when the electronic component is mounted on the engine.

[0018]

2 ≦ D1 ≦ 3.5 3 ≦ D2 ≦ 4 L1 ≦ 15D1-20 In the invention according to claim 7, the heating element (30) is energized by applying a rated voltage to the glow plug. The surface temperature of the step (36) when the temperature of the heating element is saturated is 520 ° C. or less.

According to an experimental study by the present inventors, if the surface temperature is 520 ° C. or less, the effect of the first aspect of the present invention is
It can be exerted for a longer period of time, and the reliability of the glow plug can be further increased.

The reference numerals in parentheses of the above means are examples showing the correspondence with specific means described in the embodiments described later.

[0021]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 1 is a longitudinal sectional view showing the entire configuration of a glow plug G1 according to the embodiment of the present invention, and FIG.
Is a sectional view showing a state in which the glow plug G1 is attached to the engine head 900 of the engine. FIG. 3 is an enlarged sectional view showing the vicinity of the heating element 30 in FIG.

The glow plug G1 is attached to, for example, a mounting hole (glow hole) 901 formed in a plurality (for example, four cylinders) of engine heads 900 of a direct-injection diesel engine of an automobile. It is applied to promote the ignition and combustion of the fuel in.

Reference numeral 10 denotes a cylindrical housing that can be attached to the engine, and is made of a conductive material (for example, an iron-based material). On the outer peripheral surface between one end 11 and the other end 12 of the housing 10, a mounting screw portion 13 and a nut portion 14 for screw tightening are formed.

As shown in FIG. 2, the glow plug G1 is inserted into the hole 901 of the engine head 900 while the one end 11 side of the housing 10 is positioned on the combustion chamber 902 side, and the screw portion formed in the hole 901 is formed. (Not shown) and the mounting screw 13 are screwed together via a nut 14. Thus, the glow plug G1 is detachably attached to the engine head 900.

Here, the one end 11 of the housing 10 is tapered, and in an attached state, by being in close contact with a seating surface 903 in the hole 901 of the engine head 900, airtightness in the combustion chamber 902 is maintained. It has become.

The housing 10 can be formed by, for example, using carbon steel or the like, forming the inner and outer surfaces by cold forging, and then forming the mounting screw portion 13 by cutting or the like. The dimensions of the mounting screw portion 13 may be, for example, M8 or less, which is specified in JIS (Japanese Industrial Standard).

In the inner hole of the housing 10, a cylindrical sleeve 20 made of a heat-resistant and corrosion-resistant alloy (for example, stainless steel) is accommodated. The other end 22 of the sleeve 20 is inserted into the housing 10 with one end 21 protruding from the one end 11 of the housing 10. Here, the housing 10 is press-fitted or brazed at the insertion portion.
Is fixed to the outer surface of the sleeve 20 without a gap, and the sleeve 20 is held by the housing 10.

In the inner hole of the sleeve 20, a ceramic rod-shaped heating element 30 that generates heat when energized is accommodated. The heating element 30 has the other end 32 inserted into the sleeve 20 with one end 31 protruding from the one end 21 of the sleeve 20. Here, by brazing the insertion part,
The heating element 30 is fixed and held on the sleeve 20.

The heating element 30 includes a U-shaped heating section 33 made of a conductive ceramic (for example, composed of silicon nitride and molybdenum silicide), and a heating section 33 electrically connected to the heating section 33. A pair of lead wires 34 made of tungsten or the like for conducting electricity are provided, and the heat generating portion 33 and the lead wires 34 are embedded in an insulator 35 made of an insulating ceramic (for example, containing silicon nitride as a component). It is a sintered body.

The heating element 30 has a stepped portion 36 in the middle.
The one end 31 has a small diameter portion 37 and the other end 32 has a large diameter portion 38, and the one end 31 has a spherical shape.
Here, as shown in FIG. 3, when the diameter of the small diameter portion 37 is D1 and the diameter of the large diameter portion 38 is D2, the height of the step portion 36 represented by (D2−D1) / 2 is In order to form the 37 and the large-diameter portion 38, the thickness is at least 0.05 mm or more.

Here, in the present embodiment, the heating element 3
The main feature is that all the large-diameter portions 38 of 0 are arranged in the sleeve 20. In particular, it is preferable that all of the large-diameter portion 38 and the stepped portion 36 are arranged in the sleeve 20 as in the illustrated example.

In the heating element 30, the connection between the heating section 33 and the lead wire 34 is located in the large diameter section 38 and in the sleeve 20. Further, it is preferable that the step portion 36 has an R shape so that the diameter gradually decreases from the large diameter portion 38 toward the small diameter portion 37 as shown in the figure. In addition, it may be tapered.

A rod-shaped center shaft 40 made of carbon steel processed by cutting and cold forging is housed in the other end 12 of the housing 10 in the inner hole of the housing 10. A cap lead 50 made of a conductive metal such as stainless steel is fitted to one end 41 of the center shaft 40.

Then, one lead wire 34 of the heating element 30
Are the cap leads 5 at the portions exposed from the insulator 35.
0 to the center shaft 4
0 is electrically connected. The other lead 34 is
The portion exposed from the insulator 35 is connected to the sleeve 20 by brazing or the like, thereby being grounded to the housing 10 via the sleeve 20.

The other end 42 of the center shaft 40 projects from the other end 12 of the housing 10.
A terminal screw portion 43 is formed to which an external wiring member (not shown) electrically connected to a power supply (not shown) is screwed.

Here, between the other end 42 of the center shaft 40 and the housing 10, a cylindrical insulating bush 60, a center shaft 40
An electrically insulating member such as an annular welded glass 62 and an insulator 64 for holding / fixing and centering is provided. Welding glass 62 and insulator 64
Are fastened and fixed via an insulating bush 60 by a nut 44 provided on the terminal screw portion 43.

Next, the glow plug G
The manufacturing method 1 will be specifically described. The heating element 30
As described in Japanese Patent Application Laid-Open No. 2000-130755, molding is performed by hot pressing or the like, and a small-diameter portion 37, a large-diameter portion 38, and a spherical surface of one end 31 are formed by polishing or the like.

Next, the center shaft 4 is connected via the cap lead 50.
0 and one of the lead wires 34 of the heating element 30 are fixed by brazing. Further, the heating element 30 is inserted into the sleeve 20, and the insertion portion and the other lead wire 34 and the sleeve 20 are brazed and fixed. Thus, an integrated member in which the heating element 30, the center shaft 40, and the sleeve 20 are integrated is completed.

Then, the above integrated member is connected to the housing 10.
And the insertion portion between the housing 10 and the sleeve 20 is brazed and fixed. The insertion portion may be fixed by press-fitting.

Subsequently, the insulating bush 60 and the welding glass 6
The nut 44 is tightened along the terminal screw part 43 while disposing the insulator 2 and the insulator 64 around the center shaft 40.
The welding glass 62 is supplied in a powder form, and is heated and welded. Thus, the glow plug G1 shown in FIG. 1 is completed.

The glow plug G1 is connected to the engine head 900 through the mounting screw 13 as shown in FIG.
Is screwed and attached to the hole 901. One end 31 of the heating element 30 is connected to the combustion chamber 902 of the engine.
Will be exposed.

In a state where the glow plug G1 is attached to the engine head 900, the external screw member electrically connected to the power supply is connected to the terminal screw portion 43 by tightening a terminal nut (not shown). Assembled.
Thereby, the housing 10 and the engine head 90
0 is the ground side, the external wiring member from the power source,
, The heating element 30 can be energized.

In the glow plug G1, the power is supplied to the heating element 30 so that the heating section 3 of the heating element 30 is heated.
3 generates heat, and the heat ignites the fuel in the combustion chamber 902. Thus, ignition and combustion of fuel at the time of starting the engine are promoted.

According to the present embodiment, a step portion 36 is provided in the middle, and one end 31 has a small diameter portion 37 and the other end 32 has a step portion 36.
In the heating element 30 having the large-diameter portion 38 on the side, the entire large-diameter portion 38 is arranged in the sleeve 20.

According to this, by arranging all of the large-diameter portion 38 of the heating element 30 in the sleeve 20, at least a part of the step portion 36 comes into contact with the sleeve 20, and the step portion 36 fixes the sleeve 20. It becomes easier to dissipate heat. Therefore, the heat drawing property of the step portion 36 is improved, and the thermal stress of the step portion 36 can be reduced.

In particular, as shown in the illustrated example, if all the steps 36 are arranged in the sleeve 20, the sleeve 2
This is preferable because the heat radiation of the step portion 36 through the zero can be made more remarkable, and the effect of reducing the thermal stress by improving the heat drawing property of the step portion 36 can be achieved at a higher level.

Further, according to the present embodiment, the connecting portion between the heat generating portion 33 and the lead wire 34 is located at the large diameter portion 38 and within the sleeve 20 so that the heat generating portion 33 and the lead wire 34 The thermal stress generated in the connecting portion can be reduced, and damage to the connecting portion due to the thermal stress can be suppressed.

Further, in this embodiment, since the step portion 36 of the heating element 30 has an R shape or a tapered shape, the strength of the step portion 36 can be made relatively strong.
preferable.

The diameter D1 of the small diameter portion 37 and the large diameter portion 3
8, a small diameter portion 37 including the step portion 36.
Each dimension such as length L1 (see FIG. 3) is expressed in units of mm.
Is preferably set so as to satisfy the relationship represented by the following Expression 3.

[0050]

## EQU3 ## 2 ≦ D1 ≦ 3.5 3 ≦ D2 ≦ 4 L1 ≦ 15D1-20 The lower limit of the diameters D1 and D2 is determined because if the diameter is smaller than this, the strength becomes practically insufficient. , The diameter D
The upper limits of D1 and D2 are based on a demand for a smaller glow plug.

The length L1 is set to (15D1-20) mm
The following is based on the result of examining the strength of the heating element 30 by an actual machine vibration test (with electricity) performed by the inventor. FIG. 4 shows an example of the result. In FIG.
Regarding variously changed diameter D1 and length L1;
After 8 hours (corresponding to 4 × 10 ⁷ vibrations),
The case where the heating element 30 is broken is plotted as “x”, and the case where there is no abnormality without breaking is plotted as “○”.

The approximate line S in FIG. 4 is L1 = 15D1-2.
However, as can be seen from FIG. 4, the strength of the heating element 30 is secured against vibration in the approximate line S and in a range below the approximate line S, and in a range above the approximate line S, The heating element 30 is easily broken by vibration.

Therefore, the length L1 is set to (15D1-20) m
If m or less, it is possible to provide a glow plug that is strong against vibration (engine vibration) applied when mounted on an actual machine (engine), in addition to the effect of reducing the thermal stress at the stepped portion 36 described above.

In this embodiment, the rated temperature is applied to the glow plug G1, the heating element 30 is energized, and when the temperature of the heating element 30 is saturated, the surface temperature of the step portion 36 is 520 ° C. or less. Preferably, there is.

This is based on the result of an energization test performed by the inventor as shown in FIG. The energization test was performed with the energization pattern shown in FIG. A rated voltage (for example, 11 V) is applied to the glow plug G1 to saturate the surface temperature of the small-diameter portion 37 including the stepped portion 36 (that is, the heating element having the length L1).

At this time, as shown in FIG. 5B, the surface temperature of the step 36 is changed to 480 ° C. to 550 ° C. This can be achieved by appropriately changing the shape and dimensions of the heating element 30 within the scope of the present embodiment. For example, it is possible to change the degree of retraction of the step portion 36 into the sleeve 20 or the like.

As shown in FIG. 5B, when the surface temperature of the stepped portion 36 was 550 ° C., cracks occurred in the stepped portion 36 in 4000 energization cycles (judgment x).
At a surface temperature of 520 ° C. or lower, no crack was generated in the stepped portion 36 even after 7000 energization cycles (judgment ○).

Accordingly, from the results shown in FIG. 5, the surface temperature of the step portion 36 when the rated voltage is applied to the glow plug G1 to energize the heating element 30 and the temperature of the heating element 30 is saturated is 520 ° C. or less. If it is (preferably 500 ° C. or less), the effect of reducing the thermal stress of the stepped portion 36 can be exhibited for a longer period, and the reliability of the glow plug can be further increased.

(Other Embodiments) In the above embodiment, the U-shaped heating element 30 employs a shape in which the width of the bent portion is narrower than other portions (see FIG. 3). However, as shown in FIG. 6, the same effect as in the above embodiment can be obtained even when a U-shape having a uniform width over the entire heating element 30 is employed.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an entire configuration of a glow plug according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a state where the glow plug shown in FIG. 1 is attached to an engine head.

FIG. 3 is an enlarged sectional view showing the vicinity of a heating element in FIG. 1;

FIG. 4 is a diagram showing the result of examining the strength of the heating element with respect to vibration when the diameter D1 and the length L1 of the small diameter portion are changed.

FIG. 5 is a diagram showing the results of a power distribution test on a heating element.

FIG. 6 is a diagram showing another example of the shape of the heating element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... housing, 11 ... one end of housing, 20 ... sleeve, 21 ... one end of sleeve, 22 ... the other end of sleeve, 30 ... one end of heating element, 31 ... one end of heating element, 32 ... the other end of heating element, 33 ... heat generation Part, 34 lead wire, 35 insulator, 36 step part, 37 small diameter part, 38 large diameter part.

Claims (7)

[Claims] 1. A cylindrical housing (10) attachable to an engine, wherein one end (21) is inserted into the housing while the other end (22) is inserted into the housing with one end protruding from one end (11) of the housing. A cylindrical sleeve (20) held by the housing; and one end (31) protruding from the one end of the sleeve while the other end (32) is inserted into the sleeve, whereby the sleeve is held by the sleeve; In a glow plug including a ceramic rod-shaped heating element (30) that generates heat when energized, the heating element has a step portion (36) at an intermediate portion, the one end side has a small diameter portion (37), and the other end side has a stepped portion. A glow plug having a large-diameter portion (38), wherein all of the large-diameter portion is disposed in the sleeve. 2. The glow plug according to claim 1, wherein all of the steps (36) are arranged in the sleeve (20). 3. The heating element (30) includes a heating section (33) made of conductive ceramic and a lead wire (34) electrically connected to the heating section to energize the heating section. The heat generating portion and the lead wire are embedded in an insulator (35) made of insulating ceramic, and a connecting portion between the heat generating portion and the lead wire is located at the large diameter portion (38). Glow plug according to claim 1 or 2, characterized in that it is located in the sleeve (20). 4. The height of the step (36) is 0.05.
The glow plug according to any one of claims 1 to 3, wherein the diameter is not less than mm. 5. The glow plug according to claim 1, wherein the step (36) has an R shape or a tapered shape. 6. When the diameter of the small diameter portion (37) is D1, the diameter of the large diameter portion (38) is D2, and the length of the small diameter portion including the step portion (36) is L1, Each dimension D
1, D2, and L1 satisfy a relationship expressed by the following formula 1 (unit: mm): 2 ≦ D1 ≦ 3.5 3 ≦ D2 ≦ 4 L1 ≦ 15D1-20 The glow plug according to any one of claims 1 to 5, wherein 7. The surface temperature of the step portion (36) when a rated voltage is applied to the glow plug to energize the heating element (30) and the temperature of the heating element is saturated is 520 ° C. or less. The glow plug according to any one of claims 1 to 6, wherein