JPH0133983Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to glow plugs used for preheating the sub-combustion chamber or combustion chamber of diesel engines, and specifically describes two types of glow plugs that can function as a self-temperature control type. This invention relates to an improvement in a glow plug equipped with a heating element.

[Conventional technology]

In general, diesel engines have poor startability at low temperatures, so by installing a glow plug in the auxiliary combustion chamber or combustion chamber and passing an electric current through it to generate heat, it is possible to raise the intake air temperature or use it as an ignition source to improve engine startability. A method has been adopted to improve the By the way, what is required of this type of glow plug is that it can function as a fast heating type by improving its temperature rise characteristics by supplying a large amount of power to the heating element built inside at the initial stage of energization, and that it can function as a fast heating type. In order to prevent melting, etc., the saturation temperature is set to an appropriate value to prevent overheating.
The objective is to satisfy the following performance requirements: stable heat generation characteristics can be obtained, and durability against exposure to high-temperature gas in the sub-combustion chamber or combustion chamber can be guaranteed.

The conventionally well-known general sheath type glow plug, in which a heat-resistant metal sheath is filled with heat-resistant insulating powder and a coil-shaped heating element made of a type of material such as nickel is embedded, has a power supply of is limited to prevent adverse effects on various parts including the heating element, which poses a problem in terms of temperature rise characteristics, and in order to function as a fast heating type,
In order to prevent overheating of the heating element, it is necessary to provide a separate temperature control means, which has the drawback of increasing the cost of the entire device.

In addition, a glow plug that uses heating elements each made of two types of materials with different temperature coefficients of resistance has been proposed as a device that improves the temperature rise characteristics described above and has self-temperature control means. Although such a structure functions as a fast-heating type to some extent, it is difficult to manufacture and expensive, and its heat generation characteristics are not good, so it is difficult to say that it can satisfy all of the above-mentioned performances. . This is because in conventional glow plugs of this type, a heating element with a small temperature coefficient of resistance is provided at the tip side, and a heating element with a large temperature coefficient of resistance is placed on the rear end side, and resistance changes due to temperature changes in the heating element on the rear end side. Immediately after energization, a large amount of power is supplied to the tip side heating element to quickly make it red hot, but since both heating elements are placed too close to each other, the rear side heating element is placed too close to the tip side. This is due to the fact that the temperature rises too quickly due to the thermal influence from the tip, and this causes the power supply to the tip side to be controlled. Due to these problems, it lacked heat generating properties and was unable to exhibit its effectiveness as a rapid heating type.

For this reason, the present applicant has conducted various research and development efforts to effectively utilize the advantages of using a heating element made of two types of materials as described above. Focusing on the fact that the high current conduction time at the initial stage of energization is shortened due to thermal effects due to the close proximity of the
In Japanese Patent No. 182026, we have previously proposed an inexpensive self-temperature-controlled glow plug for diesel engines that can provide stable and rapid heating properties.

To briefly explain this using FIGS. 2 and 3, reference numeral 1 in the figure is a sheath made of a heat-resistant metal material such as stainless steel, 2 is a housing that holds this sheath 1 at the tip, and this housing 2 An electrode rod 4 is concentrically attached to the rear end of the electrode rod 4 via an insulating bush 3, and the tip of the electrode rod 4 is inserted into the sheath 1.

In the inner space on the distal end side of the sheath 1,
The first helical heating element 5 (hereinafter referred to as the first
heating element) is arranged along the axial direction,
One end thereof is electrically connected to the sheath 1. Further, in the rear end side internal space of the sheath 1,
A material such as nickel or low carbon steel with a carbon content of 0.25% or less (hereinafter referred to as low carbon steel) is connected between the first heating element 5 and the electrode rod 4 on the rear end side of the sheath 1. A second spiral heating element 6 made of a conductive material with a large positive temperature coefficient of resistance.
(hereinafter referred to as a second heating element) is disposed, and furthermore, both of these heating elements 5 and 6 are embedded in a heat-resistant insulating powder 7 such as magnesia (MgO) filled in the sheath 1.

Here, the second heating element 6 not only acts as a heat generation source itself, but also supplies a large amount of electric power to the first heating element 5 because its resistance value is small immediately after the start of energization. The resistance value increases as the energization time elapses, reducing the power supplied to the glow plug, keeping the saturation temperature of the glow plug itself low, and also functioning as a temperature control means to prevent overheating. This is clear from the fact that the resistance value of the second heating element 6 increases as heat is generated due to energization.

In order to appropriately control the current by the second heating element 6, the first heating element 5 and the second heating element 6 are connected to each other.
The heating element 6 is connected to the heating element 6 in such a manner that the respective spiral portions face each other with a predetermined gap (GAP) therebetween. That is, by providing a certain gap between the spiral portions of both heating elements 5 and 6, the time interval can be maintained to prevent the thermal influence from the first heating element on the second heating element 6, which has been a problem in the past. , thereby temporally delaying the current control by the second heating element 6 to extend the time for supplying large power to the first heating element 5,
This makes it possible to rapidly heat up the first heating element 5 and significantly improve the temperature rise characteristics.

Note that these heating elements 5 and 6 have linear ends extending in the axial direction from the final helical end ends 5a and 6a of each heating element, respectively, so that heat transfer within the gap is minimized. The end surfaces of 5b and 6b are brought into contact and connected by plasma arc welding or the like. Reference numeral 8 in the figure denotes a guide rod made of a heat-resistant insulating material such as ceramic, which is disposed penetrating through the above-mentioned heating elements 5 and 6 and holds them in a predetermined position, and is used to maintain the space between the heating elements 5 and 6. It is useful for maintaining the temperature appropriately and stabilizing the heat generation characteristics.

According to such a configuration, immediately after the start of energization, since the resistance of the second heating element 6 is small, a large amount of electric power is concentrated on the first heating element 5, which is clear from the characteristic curve indicated by a in FIG. It can reach up to 230W and generates heat quickly. Furthermore, there is a time delay before the thermal influence from the first heating element 5 is transmitted to the second heating element 6 and its resistance value increases due to the existence of the gap described above. Since it takes a long time for large electric power to concentrate on the body 5, the rapid heating properties of this part are improved.

On the other hand, as is clear from the characteristic curve indicated by b in the same figure, the second heating element 6 is also supplied with nearly 100 W of power, which gradually generates heat, and the difference between the heat generation temperature and the first heating element 5 increases. The resistance value increases with the thermal influence of When the supplied current decreases due to this change in resistance value and the voltage applied to the first heating element 5 decreases, the supplied power to the first heating element 5 decreases rapidly, limiting the amount of heat generated. Overheating is prevented. Of course, at this time, the second heating element 6 also acts as a heating element itself, and the sheath 1 is thereby heated one after another and the temperature rises to the temperature required for starting the engine (usually 800° C.).

The heat generation characteristics of such a glow plug are shown as c in FIG. 5, and the temperature rise characteristics were significantly improved compared to the conventional gapless type shown as d in the same figure.

[The problem that the idea aims to solve]

By the way, in the above-mentioned glow plug for a diesel engine, the sheath 1 filled with heat-resistant insulating powder 7 in which the first and second heating elements 5 and 6 are embedded generally has a structure as shown in FIGS. 6a and 6b. , swage processing is performed during assembly, and in this case, some problems arise in the connection portion within the gap between the two types of heating elements 5 and 6 mentioned above.

To explain this in detail, the swage processing described above is
The heat-resistant insulating powder 7 filled in the sheath 1 is densely packed to improve its thermal conductivity, and
This is necessary to completely bury both heating elements 5 and 6, which are wire rods, to prevent their oxidation and improve their durability. This swaging process is performed by circling the outer periphery of the sheath 1, as shown in FIG. The sheath 1 is compressed in the radial direction by pressing the entire circumference from the direction shown in FIG.
As is clear from the figure, it is reduced in the radial direction and slightly elongated in the axial direction, making it elongated.

On the other hand, inside the sheath 1, which is reduced in the radial direction in this way, the heat-resistant insulating powder 7 is tightened throughout and condensed to a desired density,
With this powder 7, the spiral parts (indicated by 5c and 6c in the figure) of both heating elements 5 and 6 are formed as shown in Fig. 7a.
Its coil diameter is reduced. However, the wire diameter in the spiral portions 5c and 6c of both heating elements 5 and 6 becomes thicker from _D1 to _D2 due to the compressive force from the wire axis direction, as shown in a and b in the figure. has been confirmed. This is because the force from the circumferential direction is balanced in each helical portion 5c, 6c where the coil diameter is reduced, but a large compressive force is applied from the axial direction, and the volume of each heating element 5, 6 remains unchanged. Therefore, to compensate for this, the wire diameter had to be increased.

On the other hand, at the straight end portions 5b and 6b that connect the two heating elements 5 and 6 with a predetermined gap, the forces from each direction are balanced as shown in FIG. Almost no change
On the contrary, the wire diameter may be slightly reduced due to the tensile force acting on both ends in the axial direction, and as a result, there is a difference in wire diameter between the wire diameters of the spiral portions 5c and 6c of the heating elements 5 and 6, which have larger diameters. It was something that would happen.

Therefore, according to such a glow plug, the spiral portions 5c, 6 of both heating elements 5, 6
c and straight end portions 5b, 6b which are the connecting portions thereof.
Since there is a difference in the wire diameter between the two, the current density will be different between the two, and the current density will be particularly high at the connection between the linear ends 5b and 6b, which have small diameters, leading to a rise in temperature. This was a problem in terms of durability. In other words, as mentioned above, if there are thin wire diameter parts in the heating elements 5 and 6, this will not cause much of a problem during normal preheating, but if the battery voltage suddenly increases, for example during afterglow immediately after starting the engine. When this occurs, the heat dissipation in the narrow diameter portion is not enough, and the temperature in this portion rises rapidly, causing problems such as rapid deterioration and wire breakage, which adversely affects durability. In particular, this type of glow plug is required to have durability that can be used repeatedly for more than 10 years, and as mentioned above, the connection using the straight end portions 5b and 6b, which have relatively small diameters, is desirable. The existence of parts was a problem.

This means that by swaging, for example, the sheath diameter can be changed from 6φ to 5φ, and the coil diameter of the heating elements 5 and 6 can be changed.
It was reduced from 2.8φ to 2.2φ, while the heating element spiral portion 5c,
When the wire diameter of 6c increases from 0.3φ to 0.37φ and the wire diameter of the straight end portions 5b and 6b which are the connecting portions is 0.3φ, the current density I of the spiral portions 5c and 6c
Current density I of COIL and straight ends 5b, 6b
STRAT has the following relationship: I COIL: I STRAT = 1/S COIL: 1/S STRAT = 1/(0.37) ² : 1/(0.3) ² = 1: 1.5, and the temperature at the connection part tends to rise. It is easy to understand that it is a thing. In addition, S
COIL is the cross-sectional area of the spiral portion, and S STRAT is the cross-sectional area of the straight end.

[Means to solve the problem]

In order to solve the above-mentioned problems, the glow plug for a diesel engine according to the present invention has two types of heating elements made of materials with different positive temperature coefficients of resistance, and a helical shape of both heating elements. The ends of the two heating elements are connected by a linear connection part within a predetermined gap, and auxiliary bars made of conductive material are overlapped and arranged in parallel along the linear connection part within the predetermined gap between both heating elements. It is bonded and fixed in this state.

[Effect]

According to the present invention, the cross-sectional area of the straight connecting part that connects both heating elements within a predetermined gap is larger than that of the spiral part of the heating element due to the existence of the auxiliary bar installed in parallel between both ends. Therefore, even if the wire diameter of both heating element helices becomes larger due to swaging, the cross-sectional area at the connection part is maintained to be approximately the same or larger, thereby reducing the current flow at this connection part. It is possible to keep the density low, prevent temperature rise, and improve durability.

〔Example〕

Hereinafter, the present invention will be explained in detail using embodiments shown in the drawings.

1a and 1b show an embodiment of a glow plug for a diesel engine according to the present invention,
In these figures, the same or corresponding parts as in FIG.

Now, according to the present invention, a straight connection part (indicated by reference numeral 10 in the figure) that connects the first and second heating elements 5 and 6 having different temperature coefficients of resistance within a predetermined gap (GAP) is cut. The area of this linear connection 10
By overlapping and connecting and fixing auxiliary bars 11 made of conductive material between both ends along the swaging process, the heating element spiral portions 5c and 6c are substantially larger than the respective heating element helical portions 5c and 6c, which become larger in diameter by swaging. The feature is that it is configured so that

To explain this in detail, as shown in FIG. To solve the problem that the current density is high at the connecting part 10 where the diameter is relatively small, causing a temperature rise in that part, which impairs the durability. Therefore, the connection part 10 of both heating elements 5, 6
is formed in advance to have a large cross-sectional area using the auxiliary bar 11, and the heating element spiral portion 5 has a large diameter cross-sectional area at the connecting portion 10 even after swaging.
It is constructed so that it does not become smaller than the portions c and 6c. According to such a configuration, the cross-sectional area at the connecting portion 10 of both heating elements 5 and 6 is
It becomes larger by the amount that the auxiliary bar 11 is provided,
As a result, the heating element spiral portions 5c and 6 can be swaged.
Even if the wire diameter of c becomes thicker, the cross-sectional area at the connecting part 10 can be made larger than this, thereby lowering the current density in this part and preventing the temperature from rising. This provides advantages such as improved durability.

In particular, in a configuration in which the cross-sectional area at the connecting portion 10 is substantially increased by adding such an auxiliary bar 11, the size and length of the cross-sectional area of the auxiliary bar 11 can be adjusted by changing the helical portion 5c by swaging, This can be easily dealt with depending on the large diameter condition of 6c, and its advantages are great.

In addition, in this embodiment, when connecting both heating elements 5 and 6 within a gap, one linear end 5b is joined and fixed to the other spiral end 6a in a crossed state, and the straight A case is shown in which auxiliary bars 11 are arranged side by side along the shaped end portion 5b. According to such a connection structure, the linear end portion 5 is attached to only one heating element 5.
It is only necessary to form b, and both of these heating elements 5 and 6
Not only is the molding processability etc. of
It is also excellent in terms of workability when welding and connecting both heating elements 5 and 6. That is, one straight end 5
It is better to cross the spiral end 6a on the other side from the outside and weld it in that state, which has an obvious advantage over the conventional butt welding of both ends. Will. Further, such a connection structure has the advantage that relative positional deviation between the two heating elements 5 and 6 can be tolerated to some extent, and is advantageous in ensuring concentricity between the two. However, it goes without saying that the connection structure is not limited to this.

Note that the present invention is not limited to the structure of the embodiment described above, and the shape and structure of each part may be modified and changed as appropriate. For example, the structure of the auxiliary bar 11 attached to the connecting portion 10 may be modified as appropriate. can be considered. In particular, in such a connection part 10, it is desirable that the resistance of this part is small;
It is preferable to set the cross-sectional area of the auxiliary bar 11 as appropriate.
Furthermore, as a method for connecting both heating elements 5, 6 and the auxiliary bar 11 at this connecting portion 10, various joining methods including laser spot welding can be considered.

Further, according to the present invention, the applicable glow plug structure is not limited to the one illustrated in FIGS. 2 and 3, but the point is that a linear connection portion is provided between the ends of each spiral portion to provide a predetermined gap. Any structure may be used as long as it has a heating element made of two materials connected at a distance, and these heating elements are embedded in heat-resistant insulating powder within a sheath to be swaged.

[Effect of idea]

As explained above, according to the glow plug for a diesel engine according to the present invention, the cross-sectional area of the linear connection part that connects two types of heating elements with different positive temperature coefficients of resistance within a predetermined gap is By using an auxiliary bar made of material, the wire diameter of each heating element spiral part becomes larger during swaging, so despite the simple structure, the wire diameter of the spiral part becomes thicker during swaging during assembly. However, the cross-sectional area of the connection can be kept equal to or greater than this, thereby keeping the current density at the connection low, preventing problems such as temperature rise, and greatly improving durability. It has great practical effects, such as being able to maintain concentricity by stably connecting both heating elements.

[Brief explanation of the drawing]

Figures 1a and b are enlarged side views and cross-sectional views of essential parts of an embodiment of a diesel engine glow plug according to the present invention, and Figure 2 is an overall view of a diesel engine glow plug to which the present invention is applied. A schematic vertical sectional view, FIG. 3 is an enlarged sectional view of the main part, FIGS. 4 and 5 are characteristic diagrams, and FIGS. FIG. 3 is a diagram for explaining a deformed state of a heating element and the like. DESCRIPTION OF SYMBOLS 1... Sheath, 2... Housing, 4... Electrode rod, 5, 6... First and second spiral heating elements, 5
b, 5b... linear portion for connection, 5c, 6c...
Spiral part, 7... Heat-resistant insulating powder, 8... Guide rod,
10... Connection portion, 11... Auxiliary bar made of conductive material.

Claims (1)

[Claims for Utility Model Registration] (1) A first spiral heating element, which is connected in series to the first spiral heating element and has a temperature coefficient of resistance more positive than that of the first spiral heating element. The first spiral heating element includes a second spiral heating element made of a large material, and a sheath that covers and swages both heating elements while being embedded in heat-resistant insulating powder. A gap is provided between the end of the helical part of the body and the second spiral heating element, and within this gap, both heating elements are connected by a linear connection part, and at the same time, a linear connection part within the gap of both heating elements is connected. On the other hand, a glow plug for a diesel engine is characterized in that auxiliary bars made of a conductive material are arranged side by side and bonded and fixed along the line from the end of one heating element side to the end of the other side. (2) The first helical heating element and the second helical heating element are joined by crossing a linear end extending from one helical end to the other helical end. The glow for a diesel engine according to claim 1 of the utility model registration claim, characterized in that an auxiliary bar made of a conductive material is juxtaposed and bonded and fixed along the linear end portion of the diesel engine. plug.