JPH08200676A - Glow plug for diesel engine - Google Patents

Abstract

PURPOSE: To provide a high heat-resistant glow plug which can be used in a high temperature region in order to improve a characteristic deteriorated when a diesel engine is to be adapted to the regulation on exhaust gas. CONSTITUTION: A sheath heater 23 in a glow plug 10 for a diesel engine is provided with a heat generating resistor 20 and a controlling resistor 22. At least the heat generating resistor is formed by platinum alloy material. In addition, a sheath 11 is formed by a high heat-resistant metallic material having a less content of iron. In addition, a controlling resistor is formed by either a cobalt alloy material having a higher positive resistance-temperature coefficient than that of the heat generating resistor or a nickel alloy material containing pure nickel and yttrium (Y). In this case, the controlling resistor may be formed of cobalt-iron alloy material with an iron inclusion being 8wt.% and the balance being cobalt.

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 sheath type heater (hereinafter referred to as a sheathed heater) used to improve the startability of a diesel engine, and it has been particularly difficult to use it conventionally. The present invention relates to a high heat-resistant glow plug suitable for use in a diesel engine that can be used in a high temperature range and that meets exhaust gas regulations.

[0002]

2. Description of the Related Art A glow plug having various structures has been known as a glow plug for improving the starting performance of a diesel engine. That is, most commonly, there is a sheath heater made of a so-called one material in which a heat-resistant insulating powder is filled in a sheath made of a heat-resistant metal and a coiled heating wire made of one material such as nickel is embedded. In addition, JP-A-5
As disclosed in Japanese Laid-Open Patent Publication No. 7-182026, a so-called resistance wire made of two kinds of metal materials having different resistance temperature coefficients is embedded in a combined state in the heat-resistant insulating powder filled in the above-mentioned sheath, that is, so-called. The one using a sheathed heater made of two kinds of materials is also known.

In particular, the latter two-material sheathed heater can supply a large amount of electric power to the heating coil immediately after energization to quickly generate heat, thereby exhibiting a function as a rapid heating type, and controlling after a predetermined time elapses. It has a temperature control function of keeping the electric power supplied to the heating coil constant by increasing the resistance value due to the temperature rise on the coil side and preventing fusing or the like due to overheating in the heating coil. As a result, not only stable heat generation characteristics can be obtained, but also an effect of self-temperature control type can be obtained. Furthermore, in such a structure,
It is not necessary to provide temperature control means for controlling the power supply on the energizing circuit to the glow plug, and the cost of the entire preheating device can be reduced.

Here, in the sheathed heater made of one kind or two kinds of materials as described above, as a heating resistor (so-called heating coil), generally, a chromium iron wire (Fe-C) is used.
r-Al alloy wire) or nickel-chromium alloy wire (Ni-
Cr alloy wire) is used to bury a heat-resistant insulating powder such as magnesia in a heat-resistant metal sheath made of stainless steel or the like. Further, in a sheathed heater made of two kinds of materials, a material which is connected in series to the above-mentioned heating coil and has a positive temperature coefficient of resistance higher than that of the heating coil, such as iron (F
An e-line), a nickel wire (Ni wire) or the like is used as a control resistor (so-called control coil).

[0005]

The maximum operating temperature of iron-chromium or nickel-chromium alloy as the material of the heat-generating resistor (so-called heat-generating coil) in the sheathed heater made of the above-mentioned one-material or two-material is 1300 for the wire rod.
The limit is ˜1350 ° C., and thus the sheath surface temperature is 1100 to 1150 ° C., which is the limit of performance. Therefore, in terms of heat generation characteristics and durability, glow plugs using such conventional sheathed heaters are used in diesel engines that are complying with the exhaust gas regulations that have been required to take measures in recent years. It was a problem.

That is, in the diesel engine, in order to comply with the exhaust gas regulations, the engine startability is deteriorated, the engine rotation does not increase when the engine is not warm immediately after the engine is started, the so-called blow-up property is deteriorated, and further the engine is warmed. When not present, white smoke is generated due to the inclusion of hydrocarbon (HC) in the exhaust gas. Then, in order to solve the problem in the case of complying with these exhaust gas regulations, the heat generation characteristics of the glow plug, especially the saturation temperature on the sheath surface is maintained at, for example, about 1200 to 1250 ° C., and after the engine is started for a certain period of time. During that time, it is necessary to keep the saturation temperature and generate heat.

However, in the conventional general sheathed heater, the limit temperature of the heating coil is too low as described above, and the heat resistance and oxidation resistance are required for use in the high temperature range of about 1200 to 1250 ° C. as described above. However, there was a problem in terms of durability and durability, and it was not possible to obtain a satisfactory diesel engine that complied with exhaust gas regulations.

[0008] That is, in order to improve the characteristics of a diesel engine, which meets the exhaust gas regulations,
It is possible to set the saturation temperature, which was a constraint from heat resistance in conventional sheathed heaters, to a high temperature above a predetermined temperature, and to maintain that high temperature state for a certain period of time even after the engine is started. It is necessary to prevent this, to secure the durability and heat resistance of the heating coil, etc., and to make the life as long as possible. It is necessary to consider such points.

The present invention has been made in view of the above circumstances, and aims to improve the characteristics of a diesel engine which enables use in a high temperature range which has been difficult to use in the past, and which meets exhaust gas regulations. Therefore, the purpose is to obtain a suitable high heat resistant glow plug.

[0010]

In order to meet such demands, in the glow plug for a diesel engine according to the present invention, the heat generating resistor is formed of a platinum alloy material having a high melting point and good oxidation resistance. Furthermore, in order to prevent the diffusion of iron into platinum, a highly heat-resistant metal material having a low iron content is used as a sheath material.

Further, the glow plug for a diesel engine according to the present invention is provided with a cap fitted and welded to the opening of the sheath tip portion in order to connect the tip of the heating resistor to the sheath. It is made of pure nickel or a nickel-based alloy material having a low chromium content.

In addition, the glow plug for a diesel engine according to the present invention is a sheathed heater made of two kinds of materials for obtaining a tip red glow type temperature distribution and increasing a room temperature resistance so that an inrush current value becomes small. The body is made of a platinum-based alloy material, and the control resistor is made of pure nickel, yttrium (Y) -containing nickel, or cobalt (Co) -based alloy having a positive temperature coefficient of resistance larger than that of, for example, iron (Fe). ) It is formed of a material such as a cobalt iron (Co-8 wt% Fe) alloy having a small content.

[0013]

According to the present invention, since the heat-generating resistor is made of the platinum alloy material, it is possible to generate heat at a high temperature. Further, since the sheath to which the heating resistor made of the platinum-based alloy material is welded and connected is formed of a high heat-resistant metal material having a low iron content, the diffusion of iron into platinum can be prevented.

Further, according to the present invention, the cap fitted into the sheath distal end opening and welded has little or no content of a material different from that of the sheath, that is, iron or chromium. By forming a certain pure nickel or nickel-based alloy material and interposing it between the heat-generating resistor and the sheath, it is possible to prevent diffusion of iron, chromium, etc. into the heat-generating resistor by the platinum-based alloy material.

Further, according to the present invention, the sheath, the cap, and the control resistor for the sheathed heater made of two kinds of materials are made of iron or chromium which is easily diffused into the platinum alloy material forming the heat generating resistor. By forming a material that is not used, or is used only in a necessary minimum amount, it is possible to prevent diffusion of iron, chromium, etc. into the platinum system at the welded joint portion by welding.

[0016]

1 to 3 show an embodiment of a glow plug for a diesel engine according to the present invention. In these drawings, a general structure of a glow plug for a diesel engine, which is designated by reference numeral 10 in FIG. Explain. Reference numeral 11 in the figure is a sheath made of a heat-resistant metal material as described later, 1
Reference numeral 2 denotes a cylindrical housing that holds the sheath 11 at its tip, and an insulating bush 13 is provided at the rear end of the housing 12.
The electrode rod 14 is concentrically attached via the, and the tip portion 14a of the electrode rod 14 is inserted into the sheath 11.

In the inner space on the distal end side of the sheath 11, as will be described later, a heat generating spiral resistor made of a conductive material having a relatively small positive temperature coefficient of resistance such as a platinum alloy material. The coil 20 is arranged along the axial direction, and one end thereof is electrically connected to the distal end side of the sheath 11. Further, in the inner space on the rear end side of the sheath 11, between the heating coil 20 and the electrode rod tip portion 14a on the rear end side of the sheath 11, a positive electrode such as a cobalt-based alloy material is formed as described later. Control coil 2 which is a spiral resistor for control formed of a conductive material having a large temperature coefficient of resistance
1 is provided.

As a result, both of these coils 20, 21
Are connected in series between the sheath 11 and the electrode rod 14. The heat generation and control coils 20 and 21 are embedded in a heat-resistant insulating powder 16 such as magnesia (MgO) filled in the sheath 11. Reference numeral 22 in the drawing denotes a linear portion which is formed in a connecting portion between the coils 20 and 21 and is configured so that the heat influence of the heat generation in the control coil 21 acts on the heat generating coil 20 side with a time lag. The gap GAP is determined according to an appropriate condition, and thus the sheath heater 23 in the glow plug 10 is configured.

Here, the heat generation of the above-mentioned heat-generating coil 20 and the energization control by the control coil 21, and the gap GAP due to the linear portion 22 between the both coils 20, 21 further influences the heat influence from the control side to the heat-generating side in terms of time. It is well known in the art to obtain the interval, and a detailed description thereof will be omitted. Further, in the glow plug 10 for a diesel engine shown in FIG. 1 described above, the configuration and the like other than those described above are substantially the same as the conventional structure, and the description and the like will be omitted.

According to the present invention, in the glow plug 10 for a diesel engine having the above-described structure, the heating coil 20 forming the sheath heater 23 is made of, for example, platinum-rhodium (Pt-Rh) alloy or platinum-iridium (Pt-).
Ir) alloy, platinum-tungsten (Pt-W) alloy, or zirconia-dispersed platinum-rhodium (Pt-Rh).
It is made of a platinum-based alloy material such as an alloy having a high melting point and good oxidation resistance.

Here, the characteristics required for the heat-generating coil 20 as such a heat-generating resistor are that it has a high melting point, that it has good resistance to oxidation at high temperatures, and that it has a large specific resistance. (15 μΩ · cm or more), small temperature coefficient of resistance, small volatility at high temperature, etc., and a material satisfying these may be selected. In addition,
The above-mentioned characteristic that the specific resistance is large is that when the specific resistance is large, the diameter of the wire can be increased, and the coil 20 can be easily handled during manufacturing.

In consideration of these conditions, when the basic physical properties of various platinum-based alloy materials are examined for use in the heating coil 20, as is apparent from Table 1 and FIG. Among them, platinum-rhodium (Pt-Rh) alloy, particularly rhodium (Rh) in 10 wt% or 20 wt%, or platinum-iridium (Pt-I)
It has been confirmed that r) alloys and the like are preferable. 2 is a characteristic diagram showing the high temperature volatilization loss of platinum and a platinum alloy in the air at 1300 ° C. with the passage of time.

[0023]

[Table 1]

By selecting the platinum alloy material of the heating coil 20 as described above, the maximum operating temperature of the heating coil 20 becomes about 1450 to 1500 ° C., which causes a in FIG.
As is clear from the exothermic characteristics shown in, the exothermic saturation temperature of about 1200 to 1250 ° C. can be secured even on the surface of the sheath 11. In addition, b in FIG. 3 is a heat generation characteristic in the conventional glow plug.

In particular, according to the present invention, the melting point of the above-mentioned heating coil 20 is increased, the oxidation resistance at high temperature is sufficient, and it can be used in a high temperature range and has a long life. It is possible to obtain the glow plug 10 having high heat resistance and having the sheathed heater 23 having excellent durability. According to such a high heat-resistant glow plug 10, engine characteristics that have been deteriorated when the diesel engine is made to comply with exhaust gas regulations, for example, engine starting and blowing performance at the time of starting are improved, and white smoke is generated. It is possible to satisfy the characteristic improvement that it can be reduced.

Further, in the present invention, when the heating coil 20 is formed of the platinum alloy material as described above,
In order to prevent the diffusion of iron into the platinum system, a highly heat-resistant metal material having a low iron content, such as nickel material (Ni), nickel alloy material, or cobalt alloy material, is used as the material of the sheath 11. That is, in the platinum-based alloy material forming the heating coil 20 described above, diffusion is promoted when iron (Fe) or chromium (Cr) is present in a certain amount or more, so that other members of the heating coil 20, for example, the tip end. This causes a problem that the oxidation resistance is deteriorated at the joint portion by welding with the sheath 11 etc. in order to solve this, and it may be formed by a material other than Fe-based material.

Further, according to this embodiment, the sheathed heater 23 made of two kinds of materials is used to obtain the tip end red heat type temperature distribution of the sheath 11 and to increase the room temperature resistance so that the inrush current value becomes small, In this case, it is also necessary to prevent the diffusion of iron or chromium into the platinum system even at the joint with the control coil 21 at the rear end of the heating coil 20. Therefore, the control coil 21 is made of pure nickel (N having a positive resistance temperature coefficient larger than that of the heating coil 21).
i), yttrium (Y) -containing nickel, or a material such as a cobalt (Co) -based alloy such as a cobalt iron (Co-8 wt% Fe) alloy having a low iron (Fe) content. Here, as the characteristics required for the material of the control coil 21 which is such a control resistor, the melting point is high, the oxidation resistance at high temperature is good, and the resistance temperature coefficient is large, It suffices to select a material that satisfies these.

According to this structure, the sheath 11 and further the control coil 21 in the sheath heater 23 made of two kinds of materials are easily diffused into the platinum alloy material forming the heating coil 20 with iron (Fe) or chromium. (Cr) is used, or it is made of a material that uses only the minimum necessary amount to prevent iron from diffusing into the platinum system, and especially to eliminate deterioration of oxidation resistance at the joint part due to welding etc., and high heat resistance Sex glow plug 10
Can function as.

Further, Co which becomes the above-mentioned control coil 21
As the —Fe alloy material, it is preferable to use, for example, an iron content of 8% by weight and the balance of cobalt. That is, cobalt (Co) is oxidation resistant,
Excellent in durability, but poor in workability. Therefore, it is desirable to use an alloy material containing Fe. Here, the content of Fe is set to 8% by weight, which is about 150
This is because no phase transformation occurs up to about 0 ° C. and there is no volume change hysteresis.

In the above-described embodiment, the sheath heater 23 has the two kinds of resistors (heat generating coil 20 and control coil 21) embedded inside the sheath 11, but the present invention is not limited to this. Even if the sheath heater 31 is made of a kind of material in which only the heating coil 30 (heating resistor) is embedded as shown in FIG. 4, the same effect can be exerted. That is, in this embodiment, the heating coil 30 in the sheathed heater 31 is formed of a platinum alloy material as in the above-described embodiments, and the sheath 11 is made of a high heat-resistant metal material having a low iron content as described above. It is good to form.

Further, according to the present invention, the adverse effect on the heating coils 20 and 30 formed of the platinum alloy material, that is, the diffusion of iron (Fe), chromium (Cr) and the like from the sheath 11 side is accompanied. It is advisable to adopt the configuration shown in FIGS. 5 and 6 so as to prevent the embrittlement of the coil material that occurs, maintain the operating temperature at a high temperature, and eliminate the problem of durability such as early disconnection. 5 shows the case where the sheath heater 23 is made of two kinds of materials, and FIG. 6 shows the case where it is made of one kind of material.
In each figure, (a) shows a state when the sheath heater 23 is assembled, and (b) shows a state in which the tip of the sheath 11 is melted by welding and sealed.

That is, in FIG. 5A and FIG. 6A, reference numeral 40 is a cap fitted into the distal end opening 41 of the sheath 11 and welded by welding. Embedded heating coils 20, 3
The tip of 0 is welded and connected by spot welding or the like, and is used when the sheath 11 and the heating coils 20 and 30 are connected. And this cap 4
No. 0 is melted by TIG welding or the like from the outside of the sheath 11 and becomes an integral body with the sheath 11 to close the distal end portion of the sheath 11, which is shown in FIGS. 5 (b) and 6 (b). As shown. Reference numeral 42 in the drawing denotes a welded portion by this welding.

In this embodiment, the cap 40 described above is used.
At the time of welding connection of the cap 40 that is directly welded to the heating coils 20 and 30, by forming pure nickel, a nickel-based alloy material, or the like, which has no iron or chromium content or contains a small amount of iron or chromium. In addition, it is possible to prevent diffusion of iron, chromium, etc. into the coil and improve heat resistance strength and durability.

Then, the cap 40 having the coils 20 and 30 thus connected is fitted into the distal end opening 41 of the sheath 11, and this portion is melted by TIG welding or the like to integrate the cap 40 with the sheath 11. If such a cap 40 is made of a material different from that of the sheath 11, diffusion of iron, chromium, etc. from the sheath 11 side to the coils 20, 30 can be suppressed, the coil material will not be embrittled, and the platinum-based material will be used. The sheath heater 23 that can achieve the effect of using the alloy material, that is, the long life even when used at high temperature
It is possible to realize the glow plug 10 provided with.

Therefore, in such a structure, as the material of the sheath 11, it is possible to use a stainless steel material, Inconel, or the like, and it is possible to achieve cost reduction, and the heating coils 20 and 30 are embrittled by the platinum alloy material. It is possible to prevent the problem of durability such as early disconnection.

Particularly, in the above-mentioned structure, the cap 40 to which the tips of the heating coils 20 and 30 are connected by welding.
As shown in FIGS. 5 (b) and 6 (b), the inner end 40a of the cap 40 is formed so as not to melt when the cap 40 is welded to the sheath 11, for example, to project into the sheath 11. It may be formed in various sizes and shapes, and the temperature conditions during welding with the sheath 11 and the welding method may be appropriately selected.

That is, the heating coil 2 of the cap 40
The welded connection with 0 and 30 is the sheath 11 of the cap 40.
It is not melted at the time of welding by welding with, so that the diffusion of iron and chromium from the sheath 11 side to the coils 20 and 30 can be prevented.

The present invention is not limited to the structure of the embodiment described above, and the shape, structure, etc. of each part of the glow plug 10 can be freely modified or changed. For example, the sheath heater 2 can be used.
A suitable modification is conceivable, such as a sheath 11 having a small diameter at the distal end thereof, or a structure for extracting the electrode rod 14 at the rear end of the housing 12 holding the sheath heater 23.

[0039]

As described above, according to the glow plug for a diesel engine of the present invention, the heating resistor embedded in the heat resistant insulating powder in the sheath forming the sheath heater is made of the platinum alloy material. Since it is formed, it has the following effects despite the simple structure.

That is, according to the present invention, the maximum operating temperature of the heating resistor is about 1450 to 1500 ° C.,
As a result, a heat generation saturation temperature of about 1200 to 1250 ° C. can be secured even on the sheath surface. In particular, since the melting point of the heat-generating resistor can be increased and sufficient oxidation resistance can be secured at high temperatures, it can be used in a high temperature range and has a durable sheathed heater that has a long service life and high heat resistance. A sex glow plug can be obtained. Then, by using such a high heat-resistant glow plug, a problem that occurs in a diesel engine when complying with exhaust gas regulations, for example, deterioration of engine startability, deterioration of blowing-up at start,
It is possible to satisfactorily improve problems in characteristics such as white smoke.

Further, according to the present invention, the cap, which is fitted and welded to the opening of the sheath tip portion in order to connect the tip of the heat-generating resistor to the sheath, is made of pure nickel containing a small amount of iron or chromium, or Since it is made of a nickel-based alloy material, this cap is interposed between the heat-generating resistor and the sheath in spite of its simple structure. It is possible to prevent the diffusion of iron, chromium, etc. to the body.

Further, according to the present invention, the heating resistor is made of a platinum alloy material and the sheath is made of a high heat resistant metal material having a low iron content, or the heating resistor is inside the sheath. A control resistor connected in series with the heating resistor for controlling the electric power supplied to the heating resistor is pure nickel having a positive temperature coefficient of resistance higher than that of the heating resistor, or nickel or cobalt alloy containing yttrium (Y). By forming the material, for example, one of the cobalt iron alloy materials, the following operational effects are obtained. That is, the sheath or the control resistor in the sheathed heater made of two kinds of materials does not use iron or chromium that easily diffuses in the platinum alloy material forming the heat generating resistor, or uses only the necessary minimum amount. It can be formed of a material to prevent the diffusion of iron into the platinum group, to eliminate the deterioration of the oxidation resistance at the joint, especially due to welding, etc., and to exhibit the function as a high heat resistant glow plug.

In particular, when the above-mentioned control resistor is formed of a cobalt iron alloy material having an iron content of 8% by weight and the balance being cobalt, the oxidation resistance is increased, the temperature control is stabilized, and the seeds are seeded. It is possible to further exhibit the above-described function and effect that the abnormal temperature rise of the heater and the heating coil can be suppressed and the durability can be improved. Further, it is possible to secure the high-temperature oxidative property of the control coil, improve the durability, and prolong the service life.

[Brief description of drawings]

FIG. 1 is a schematic side cross-sectional view of a main part configuration showing an embodiment of a glow plug for a diesel engine according to the present invention.

FIG. 2 is a characteristic diagram showing a high temperature volatilization loss of a platinum alloy material used for a heating resistor.

FIG. 3 is a characteristic diagram showing heat generation characteristics of a glow plug for a diesel engine according to the present invention in comparison with a conventional example.

FIG. 4 is a schematic side sectional view showing another embodiment of a glow plug for a diesel engine suitable for applying the present invention.

FIG. 5 shows another embodiment of the glow plug for a diesel engine according to the present invention, (a) shows a state when the cap is assembled at the tip of the sheath heater made of two kinds of materials, (b).
FIG. 7 is an enlarged cross-sectional view of a main part showing a state after welding in which the cap is welded to the sheath.

FIG. 6 shows still another embodiment of the glow plug for a diesel engine according to the present invention, in which (a) shows a state when the cap is assembled at the tip of the sheath heater made of one kind of material,
FIG. 6B is an enlarged cross-sectional view of a main part showing a state after welding in which the cap is welded to the sheath.

[Explanation of symbols]

Reference numeral 10 ... Diesel engine glow plug, 11 ... Sheath, 12 ... Housing, 14 ... Electrode rod, 14a ... Electrode rod tip portion, 16 ... Heat-resistant insulating powder, 20, 30 ... Heating coil (heating resistor), 21 ... Control Coil (control resistor), 23, 31 ... Seesheater, 40 ... Cap, 4
0a ... cap inner end, 41 ... sheath tip end opening, 42
… Welded part by welding.

Claims (5)

[Claims] 1. A glow plug for a diesel engine, comprising a sheathed heater comprising a sheath for covering at least a heat-generating resistor embedded in heat-resistant insulating powder, wherein the heat-generating resistor is a platinum alloy material. A glow plug for a diesel engine, characterized by being formed by. 2. The glow plug for a diesel engine according to claim 1, wherein the sheath is formed of a highly heat-resistant metal material having a low iron content. 3. The glow plug for a diesel engine according to claim 1, further comprising a cap fitted and welded to an opening of a sheath tip portion in order to connect the tip of the heating resistor to the sheath. A glow plug for a diesel engine, which is formed of pure nickel or a nickel-based alloy material having a low content of iron and chromium. 4. The glow plug for a diesel engine according to claim 1, claim 2 or claim 3, wherein the control is connected in series with a heating resistor inside the sheath and controls the electric power supplied to the heating resistor. The control resistor is a cobalt-based alloy material having a positive resistance temperature coefficient larger than that of the heating resistor, pure nickel, or a nickel alloy material containing yttrium (Y). A glow plug for a diesel engine, characterized by being formed by. 5. The glow plug for a diesel engine according to claim 4, wherein the control resistor is formed of a cobalt iron alloy material having an iron content of 8% by weight and the balance being cobalt. Glow plug for diesel engine.