JPH0116942Y2 - - 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.

[Prior Art] Diesel engines generally have poor startability at low temperatures, so a glow plug is installed in the auxiliary combustion chamber or combustion chamber and a current is passed through it to generate heat, thereby raising the intake air temperature or eliminating the ignition source. A method has been adopted to improve engine startability. 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.

In 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 coiled heating element made of a type of material such as nickel is buried, the power supplied to the glow plug is 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 this kind of traditional glow plug,
A heating element with a small temperature coefficient of resistance is provided on the tip side, and a heating element with a large temperature coefficient of resistance is provided on the rear side, and the resistance fluctuation due to temperature change of the rear heating element is used to make the heating element on the tip side immediately after energization. However, since both heating elements are placed too close to each other, the temperature of the heating element on the rear end rises too quickly due to the thermal influence from the front end. This is because the power supplied to the tip side is 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, and has found that in the conventional system, two types of heating elements are too close to each other. 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) are provided, and these heating elements 5 and 6 are further 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, a time interval can be maintained to prevent the thermal influence from the first heating element to the second heating element 6, which has been a problem in the past. , the current control by the second heating element 6 is delayed in time and the current control by the second heating element 6 is delayed.
This makes it possible to extend the supply time of high power to the first heating element 5, rapidly heat up the first heating element 5, and significantly improve the temperature rise characteristics.

The heating elements 5 and 6 have straight ends 5b extending in the axial direction from the final helical ends 5a and 6a of each heating element, for example, so that heat transfer within the gap is minimized. , 6b are brought into contact with each other 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 is generally as shown in FIGS. 6a and 6b. swage processing is applied during assembly.
In this case, some problems arise in the connection within the gap between the two types of heating elements 5 and 6 mentioned above.

To explain this in detail, the swage process mentioned 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 to become 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 posed 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, such as during afterglow immediately after starting the engine, When it rises, the heat dissipation in the narrow diameter part is not enough, and the temperature in this part rises rapidly.
This caused problems such as rapid deterioration and disconnection, which adversely affected durability.

This means that by swaging, for example, the sheath diameter can be changed from 6φ to 5φ, and the coil diameter of 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, 6b which are the connecting portions is 0.3φ, the current density I of the spiral portions 5c, 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 diesel engine glow plug according to the present invention has two types of heating elements made of materials with different positive temperature coefficients of resistance, and these heating elements are arranged in a predetermined manner. By forming a conductive coating layer on the connection end of each heating element, the connecting portion between the two heating elements within a predetermined gap can be made to have a diameter larger than the wire diameter of the helical portion of each heating element. It is designed to be formed as follows.

[Effect]

According to the present invention, the diameter of the connecting part that connects both heating elements within a predetermined gap becomes thicker than the wire diameter of the spiral part of the heating element due to the presence of the conductive coating layer. Even if the wire diameter of the helical part becomes thicker, the diameter of the connection part can be maintained at the same or larger diameter, thereby keeping the current density at the connection part low, preventing temperature rise, and improving durability. It is something.

〔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, parts that are the same as or correspond to those in FIG.

Now, according to the present invention, the diameter of the connecting 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 By forming a conductive coating layer 11 made of a conductive ceramic material, metal material, etc. on the outer periphery of the connecting ends of the heating elements 5 and 6, the wire diameter becomes substantially larger than the wire diameter of the heating element spiral parts 5c and 6c. It is characterized by its structure.

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 diameter using a conductive coating layer 11, and is configured so that the diameter of this connecting portion 10 does not become smaller than the wire diameter of the heating element spiral portions 5c and 6c even after swaging. According to such a configuration, both heating elements 5 and 6
The diameter at the connecting portion 10 of the conductive coating layer 1
1, so that even if the wire diameter of the heating element spiral portions 5c, 6c becomes thicker due to swaging, the cross-sectional area at the connecting portion 10 will be larger than this. This has the advantage of lowering the current density in this part, preventing temperature rise, etc., and improving durability.

In particular, in a configuration in which the connecting portion 10 is formed with a large diameter using such a conductive coating layer 11, the diameter and length of the connecting portion 10 are determined by swaging the spiral portions 5c and 6.
This can be dealt with depending on the large diameter state of c, which has great advantages.

In addition, in this embodiment, when connecting both heating elements 5 and 6 within a gap, a case is shown in which one linear end 5b is joined to the other spiral end 6a in a crossed state and fixed. ing. According to such a connection structure, it is only necessary to form the linear end portion 5b on only one heating element 5, and not only can the molding process of both heating elements 5 and 6 be easily performed, but also the It is also excellent in terms of workability when welding and connecting the bodies 5 and 6. That is, one linear end 5b is aligned with the other spiral end 6a from the outside in a crossing state,
It is better to weld in that state, and its advantage is obvious compared to the conventional case where both ends are butt welded. 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, structure, etc. of each part may be modified and changed as appropriate. For example, the formation state and thickness of the conductive coating layer 11 in the connection part 10 There are many possible variations on this. In particular, in such a connection portion 10, it is desirable that the resistance of this portion be small. Furthermore, this connection part 10
As a method for connecting both heating elements 5 and 6, various joining methods including laser spot welding can be considered.

Furthermore, according to the present invention, the structure of the glow plug to which it is applied is not limited to that illustrated in FIGS. It is sufficient if it has a structure in which it is embedded in heat-resistant insulating powder.

[Effect of idea]

As explained above, according to the glow plug for a diesel engine according to the present invention, the diameter of the connection part that connects two types of heating elements with different positive temperature coefficients of resistance within a predetermined gap can be adjusted by using a conductive coating layer. Since the diameter of the wire is larger than that of the helical part of the heating element, despite the simple structure, even if the wire diameter of the helical part becomes thicker during swaging during assembly, the connection part will not be damaged. This makes it possible to keep the current density at this connection low, prevent problems such as temperature rise, and greatly improve durability. It has great practical effects, such as the ability to maintain concentricity through stable connections between bodies.

[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, 6b... Straight portion for connection, 5c, 6c...
Spiral part, 7...Heat-resistant insulating powder, 8...Guy rod, 1
0... Connection portion, 11... Conductive coating layer.

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 and the second spiral heating element are provided with a second spiral heating element made of a large material, and a sheath that covers both heating elements by embedding them in heat-resistant insulating powder. A gap is provided between the ends of the spiral part of the body, and both heating elements are connected within this gap, and a conductive coating layer is formed at the connection end of each heating element at the connection part within the gap of both heating elements. A glow plug for a diesel engine characterized by having a diameter larger than the wire diameter of each heating element spiral part. (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. A glow plug for a diesel engine as set forth in claim 1 of the utility model registration claim, characterized in that the glow plug is connected.