JPH1089687A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug equipped with an ion detection electrode in which there is eliminated the trouble of carbon deposition, and an area of the ion detection electrode exposed to a fire is essentially increased, and further an ion detection current is accurately obtained. SOLUTION: The present glow plug comprises a housing 4 and a body 10 supported on the former. The body 10 comprises an insulator 11, an electrical heat generating body 2 and a pair of lead wires 21, 22 provided in the insulator 11, and an ion detecting electrode 3. A conductor layer 6 is provided which is provided on the surface of the insulator 11 so as to cover an exposed part of the ion detecting electrode 3 from the insulator 11 and which is electrically connected with the ion detecting electrode 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a glow plug for promoting ignition and combustion of fuel.

[0002]

2. Description of the Related Art In recent years, in gasoline engines and diesel engines, it has been demanded to further reduce exhaust gas and smoke from the viewpoint of environmental protection. And
To meet these demands, various types of engine improvement and post-treatment (catalyst purification, etc.) have been studied to reduce exhaust gas, improve fuel and lubricating oil properties, and improve various engine combustion control systems.

Further, in recent engine combustion control systems, it is required to detect the combustion state of the engine, and it is necessary to detect the combustion state of the engine by detecting the in-cylinder pressure, combustion light, ion current, and the like. Are being considered. In particular, detecting the combustion state of an engine using an ion current is considered to be extremely useful because the chemical reaction accompanying the combustion can be directly observed, and various ion current detection methods have been proposed.

For example, Japanese Patent Application Laid-Open No. 7-259597 discloses a sleeve-shaped ion detection electrode insulated from a fuel injection nozzle and a cylinder head of an engine at a mounting seat of the fuel injection nozzle. Discloses a method for detecting an ionic current associated with fuel combustion by connecting to a detection circuit. U.S. Pat. No. 4,739,731 discloses an ion current detection sensor using a ceramic glow plug.

In these techniques, a conductive layer made of platinum is attached to the surface of a heater (electric heating element) of a glow plug, and this conductive layer is insulated from a combustion chamber and a glow plug mounting bracket. Then, an ion current measuring power supply (250 V DC) is applied to the conductive layer from the outside to detect an ion current accompanying fuel combustion.

[0006]

However, all of the above-mentioned prior arts have the following problems. That is, in the former technique (Japanese Patent Application Laid-Open No. 7-259597), in order to detect an ion current, a sleeve-like ion detection electrode that is insulated from other parts must be provided. In addition, complicated work is required in the processing. Therefore, there is a problem that the ion detection electrode has a very expensive configuration. Further, there is a shortcoming that the carbon between the fuel injection nozzle and the ion detection electrode and between the ion detection electrode and the cylinder head are short-circuited by carbon generated in the combustion chamber, so that the fuel cell cannot be used at an early stage.

The latter technique (US Pat. No. 4,734,734)
No. 9,731), there is a disadvantage that the structure is complicated because the ion detecting electrode is provided separately from the current-carrying heating element and both are connected to different power sources. In addition, since a large amount of expensive noble metal such as platinum is required in order to secure the heat resistance and wear resistance of the ion detection electrode, there is a disadvantage that the glow plug itself becomes very expensive.

On the other hand, in order to solve the above various problems, Japanese Patent Application Laid-Open No. 8-147132 proposes a glow plug in which an electrode for ion detection is embedded in an insulator. With this configuration, it is possible to obtain a stable detection signal without short circuit between the ion detection electrode and the fuel injection nozzle or between the ion detection electrode and the cylinder head due to carbon generated in the combustion chamber. Was completed.

However, in the glow plug in which the ion detecting electrode is buried by the insulator, the exposed area of the ion detecting electrode to the combustion chamber becomes very small.
A new problem has been found that it is difficult to obtain a sufficient ion detection current.

The present invention has been made in order to solve such a problem, and has no problem of carbon adhesion, and can substantially increase the area where the ion detecting electrode is exposed to a flame. An object of the present invention is to provide a glow plug with an electrode for ion detection, which can accurately obtain a detection current.

[0011]

According to a first aspect of the present invention, there is provided a glow plug including a housing and a main body supported in the housing, wherein the main body includes an insulator, and an electric heating element provided inside the insulator. A pair of lead wires electrically connected to both ends of the current-carrying heating element and led out of the insulator; and a pair of lead wires disposed inside the insulator to detect an ionization state in the flame. A conductive electrode provided on the surface of the insulator so as to cover the ion detecting electrode and a portion of the ion detecting electrode exposed from the insulator, and electrically connected to the ion detecting electrode. A glow plug, wherein a layer is provided.

What is most remarkable in the present invention is that an electric heating element and an ion detection electrode are disposed inside the insulator, and a conductive layer having the above-mentioned structure is disposed on the surface of the insulator. That's what it does.

The conductive layer is provided with an area larger than the area of the exposed portion so as to cover the exposed portion of the ion detecting electrode from the insulator. The conductive layer is
It is electrically connected to the ion detection electrode and has conductivity itself. Therefore, the conductive layer plays a role of substantially expanding the area of the exposed portion of the ion detection electrode.

When disposing the energizing heating element and the electrode for ion detection in an insulator, for example, as shown in FIG. Is embedded in a ceramic powder that is a raw material of an insulator to be integrally molded. Alternatively, the current-carrying heating element and the electrode for ion detection are interposed between two separate insulators separately manufactured in advance.

[0015] These insulator molded products or the integrally molded product of the electric heating element and the ion detecting electrode are prepared by, for example, mixing these material powders with a resin containing paraffin wax as a main component and subjecting them to injection molding. It is produced by doing. Next, pressure sintering including degreasing is performed and firing is performed. Then, a ceramic heater with an ion detection function is manufactured by cylindrical grinding and spherical grinding.

Further, the current-carrying heating element and the electrode for ion detection may be provided inside the insulator by printing. An example of such printing is as follows. For example, a conductive material formed of a conductive material into a desired shape is formed on the surface of a green body formed of a ceramic material for forming an insulator by screen printing, pad printing, hot stamping, or the like. This is performed by printing the heating element, its lead wire, and the electrode for ion detection. Next, the formed form is wound,
Then, it is fired.

As a result, the printed heating element is formed,
An insulator having a built-in lead wire and an electrode for ion detection is obtained. In any of the above manufacturing methods, the electrode for ion detection is exposed on the surface of the insulator.

Next, in forming the conductive layer on the surface of the insulator, for example, the shape, roughness, etc. of the insulator are first adjusted as necessary. Next, a conductive layer is printed in a desired shape on the insulator surface by pad printing, cylindrical screen printing, or the like, and is printed. Also,
The conductive layer can be formed by plasma coating, vapor deposition, or other methods.

Next, the operation and effect of the present invention will be described.
First, the glow plug of the present invention generates heat by passing an electric current through the above-mentioned current-carrying heating element, and the heating promotes ignition and combustion in the combustion chamber. Further, the ion detection electrode detects the state of ionization in the combustion flame. That is, at the time of detecting the ion current, the ion detection electrode and the inner wall (cylinder head) of the combustion chamber adjacent to the ion detection electrode form two electrodes between the two for capturing the positive ions and the negative ions during fuel combustion. Form.

As a result, the ion current can be accurately detected, and the information can be effectively used for combustion control. In addition, since the glow plug is provided with the original function of heating the combustion chamber (glow function) and the function of detecting the ion current, the structure can be made compact and inexpensive.

In the present invention, a conductive layer electrically connected to the electrode for ion detection is provided on the surface of the insulator. Therefore, the conductive layer serves as an exposed portion of the ion detection electrode, and the area thereof is increased.
Therefore, the ion current can be detected more reliably. Therefore, the ion current can be detected with higher accuracy than in the case where the conductive layer is not provided, and the fuel control can be further improved.

Further, the glow plug of the present invention has a simple structure because the above-mentioned heating element, lead wire and ion detecting electrode are integrally provided inside the insulator. Therefore, according to the present invention, there is no problem of carbon adhesion, and the area where the ion detection electrode is substantially exposed to the flame can be increased, and the ion current can be detected with high accuracy.

Next, it is preferable that the conductive layer has an edge portion formed by partially exposing the insulator. In this case, the edge portion exhibits a property of adsorbing ions more easily than other smooth portions (edge effect). Therefore, the responsiveness of the detection of the ion current is improved, and for example, the rising angle at the time of the ion current detection described later can be made steep and the peak value can be increased.

The edge portion formed by partially exposing the insulator from the conductive layer is, for example, formed by forming the conductive layer into a mesh structure or the like and exposing the insulator between the meshes as described later. In addition to the above, it also includes an edge portion formed at the boundary between the solid conductive layer and the exposed portion of the insulator.

Further, as in the third aspect of the present invention, it is preferable that the edge portion is angular. The angular edge portion can be obtained by forming a stepped shape without smoothing a boundary portion with the insulator as shown in, for example, a first embodiment described later. In this case, the edge effect can be further increased.

Further, as in the invention of claim 4, the conductive layer may have a mesh structure, and the surface of the insulator may be exposed between the meshes (FIG. 10). FIG.
5). In this case, a large number of square edge portions can be formed in each mesh portion, and the above-described edge effect can be more reliably exerted.

Further, as in the invention of claim 5, the conductive layer can be made of metal or conductive ceramic. As the metal, it is particularly preferable to use a mixture of a high melting point metal and an active metal. In this case, the adhesion between the insulator and the conductive layer can be enhanced by the active metal, and the durability can be enhanced by the refractory metal.

Examples of the high melting point metal include platinum,
There are noble metals such as gold, nickel, iron, chromium and the like, and these can be used alone or in combination. The active metals include titanium, zirconium, hafnium, vanadium and the like, and these can be used alone or in combination. Preferably, the total of gold and nickel is 90% by weight or more, and the balance is active vanadium. In this case, gold and nickel exhibit conductivity while maintaining durability, and vanadium enhances adhesion to an insulator.

As the conductive ceramic, silicides, carbides, nitrides and borides of various metals can be used. Preferably, silicides are preferred for reasons of oxidation resistance. In addition, it is preferable that an oxide-based ceramic such as aluminum oxide or silicon dioxide is mixed with the conductive ceramic in order to improve the adhesion to an insulator.

Further, it is preferable that the conductive layer has a thickness of 1 to 20 μm. 1μ
If it is less than m, the combustion wave or the residue of the combustion violently collides, and there is a problem that the conductive layer becomes thin due to abrasion and the durability is lost, and preferably 5 μm or more. On the other hand, if the thickness exceeds 20 μm, the thermal expansion coefficient of the insulator greatly differs from that of the insulator. Therefore, there is a problem that cracks occur due to cold heat and peel off from the insulator, and preferably 15 μm or less.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 A glow plug according to an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. The glow plug of this embodiment is a ceramic glow plug used as a start-up assist device for a diesel engine. The glow plug 1 of this example is
As shown in FIG. 1, it comprises a main body 10 and a housing 4 on which the main body 10 is mounted. The main body 10 includes an insulator 11
And a current-carrying heating element 2 provided inside the insulator 11;
It has a pair of lead wires 21 and 22 that are electrically connected to both ends of the current-carrying heating element 2 and led out to the other end of the insulator.

Further, there is provided an ion detection electrode 3 disposed inside the insulator 11 for detecting the state of ionization in the flame. Further, on the surface of the insulator 11, a conductive layer 6 which is electrically connected to the ion detecting electrode 3 and has a square edge portion 61 is provided. As shown in FIG. 1, the conductive layer 6 in this example has a shape covering the tip of the glow plug main body 10 in a cap shape, and is a solid layer having an edge portion 61 only at the upper end portion.

As shown in FIGS. 1 and 2, the main body 10 is fixed in a metal housing 4 via a metal annular support 41. Then, one lead wire 21 of the current-carrying heating element 2 rises inside the insulator 11 and is electrically connected to the internal lead wire 231 via a conductive terminal portion 23 provided on a side surface of the main body 10. Have been.
Further, the other lead wire 22 is electrically connected to the internal lead wire 33 via a conductive terminal 31 provided at the upper end of the insulator 11. Note that the external lead wire 231 is
It is commonly used as a lead wire for the electric heating element 2 and the ion detection electrode 3.

On the other hand, the housing 4 is
2, and has a protective cylinder 42 at the upper part as shown in FIG. Further, the housing 4 has a male screw portion 43 for mounting to the cylinder head 45 of the engine. A rubber bush 4 is provided at the upper opening of the protection cylinder 42.
21 are fitted. External lead wires 233 and 333 are inserted through the rubber bush 421, and these are connected to the internal lead wires 231 and 33 via connection terminals 232 and 332, respectively.

Therefore, the external lead wire 233 is electrically connected to one end of the current-carrying heating element 2, and the external lead wire 333 is electrically connected to the other end of the current-carrying heating element 2. Also, the main body 1
The front end (lower end) of the zero is formed in a hemispherical shape as shown in FIG.

Next, in manufacturing the glow plug body 10, first, as shown in FIG.
And an electrode 3 for ion detection are prepared.
This integrally molded article 29 is manufactured by injection molding or press molding using ceramic powder for the electric heating element 2 and the ion detection electrode 3. And this one-piece molding 29
Are buried in the insulator 11 and are integrally pressed and fired by a hot press. Prior to the above burial,
The lead wires 21 and 22 are connected. This gives
An insulator 11 containing the electric heating element 2 and the ion detection electrode 3 is obtained.

Next, in forming the conductive layer 6 on the surface of the insulator 11, the surface of the insulator 11 is roughened, and then the conductive layer material is printed. First, the surface roughness of the insulator 11 is increased by etching with phosphoric acid or the like. In addition, for the portion where the insulator 11 is cylindrically ground, the surface roughness can be increased by using a rough grindstone of # 300 or less.
Thereby, the adhesion between the insulator 11 and the conductive layer 6 is improved.

Next, a conductive layer material is printed on the spherical portion at the tip of the glow plug main body 10 by a pad printing method, and on a cylindrical portion by a cylindrical screen printing method. At this time, printing is performed so that the conductive layer material contacts the exposed portion of the ion detection electrode. Next, the conductive layer is baked at a temperature of 900 ° C. or more in a vacuum atmosphere or a nitrogen atmosphere.
Thus, the conductive layer 6 is formed on the surface of the insulator 11 as shown in FIG. In this example, a material mainly composed of metal was used as the conductive layer material. Specifically, a mixed material of 93% by weight of Au, 5% by weight of Ni and 2% by weight of V was used. The thickness of the conductive layer was 10 μm.

Next, as shown in FIG. 4, the glow plug 1 constituted by the main body 10 and the housing 4 as described above is obtained by screwing the male thread of the housing 4 into the cylinder head 45 of the engine. Mounting.
As a result, the glow plug body 10 is mounted in a state where the tip of the glow plug body 10 projects into the swirl chamber 451 which is a part of the combustion chamber of the cylinder head 45. Reference numeral 457 indicates a main combustion chamber,
458 is a piston, and 459 is a fuel injection nozzle.

The glow plug 1 is connected to a glow plug operation circuit as shown in FIG. That is, the lead wire 21 at one end of the electric heating element 2 is connected to the external lead wire 23.
3, a glow relay 53, 531 and a 12 volt battery 54 are connected to an external lead wire 333. Further, the external lead wire 333 is
3, and through the lead wire 22 (FIG. 1) in the main body 10,
It is connected to the other end of the electric heating element 2. Thus, a circuit for heating the energizing heating element 2 is formed.

The ion detecting electrode 3 is connected to the cylinder head 45 via the external lead wire 233, the ion relay 530, the ion current detecting resistor 521, and the DC power supply 51.
It is connected to the. Further, the ion current detecting resistor 5
Reference numeral 21 denotes a potentiometer 522 for detecting an ion current.
Which is connected to an ECU (electronic control unit) 52. The glow relays 53 and 531, the ion relay 530, the engine coolant temperature sensor 525, and the engine speed sensor 526 are connected to the ECU 52.

When using the glow plug 1 shown in FIG.
The glow relays 53 and 531 are turned on by U52. Therefore, the path between the battery 54 and the heating element 2 of the glow plug is closed, and the heating element 2 of the glow plug body 10 is energized to generate heat. Therefore glow plug 1
Is in a heated state, the vortex chamber 451 is heated, and rises to the ignition temperature. Therefore, every time fuel is injected from the fuel injection nozzle 459, the fuel is ignited, the piston 458 is operated, and the engine is driven.

On the other hand, when the fuel is burning, ions are generated as described above, so that the glow relays 53, 5
31 is turned off, the ion relay 530 is turned on, and the ion current is detected by the ion detection electrode 3, the ion current detection resistor 521, and the potentiometer 522. That is, a voltage is applied between the ion detection electrode 3 of the glow plug main body 10 and the cylinder head 45 by the DC power supply 51 of 12 volts.

Then, with the generation of active ions in the combustion flame zone in the swirl chamber 451, an ion current flows through a current path including the ion current detecting resistor 521. The ion current detecting resistor 521 has a resistance of about 500 kΩ, and the ion current flowing therethrough is detected by the potentiometer 522 as a potential difference between both ends.

Here, the principle of detecting the ion current will be briefly described. The fuel injected from the fuel injection nozzle 459 is supplied to the swirl chamber 45.
When the fuel is burned in step 1, a large amount of ionized positive ions and negative ions are generated in the combustion flame zone. At this time, since a battery voltage is applied between the ion detecting electrode 3 and the cylinder head 45 facing the ion detecting electrode 3, negative ions are captured by the ion detecting electrode 3 and positive ions are captured by the cylinder head 45. Ions are captured. As a result, the above-described current path is formed, and the ion current flowing through this current path is
1 is detected as a potential difference between both ends.

On the other hand, the ECU 52 has a CPU, ROM, R
A well-known microcomputer including an AM and an input / output circuit and an A / D converter (both are not shown) are mainly configured to input a detection signal detected by the potentiometer 522. A detection signal of a water temperature sensor 525 for detecting the temperature of the engine cooling water and a detection signal of a rotation speed sensor 526 for detecting the engine speed according to the engine crank angle are input to the ECU 52. Detects the water temperature Tw and the engine speed Ne based on each detection signal.

When the diesel engine is started at a low temperature, the ECU 52 heats the current-carrying heating element 2 of the glow plug 1 to promote ignition and combustion of the fuel. Immediately after the start of the diesel engine, the ion current is detected. Note that, at the beginning of the engine start, the glow relays 53 and 531 are in an on state, and the energizing heating element 2 is maintained in a heated state.

The on / off switching process of the glow relays 53, 531 will be described below with reference to the flowchart of FIG. FIG. 5 is executed by interruption processing for a predetermined time. First, when the processing in FIG.
U52 first determines whether or not the glow relays 53 and 531 are off after the engine warm-up is completed in step S11. Step 1 at the beginning of engine start
1 is negatively determined, and the ECU 52 reads the water temperature Tw and the engine speed Ne in the following step 12.

Thereafter, at step 13, it is determined whether or not the water temperature Tw is equal to or higher than a predetermined warm-up completion temperature (60 ° C. in the present embodiment), and at step 14, the engine speed Ne is increased to a predetermined speed ( In the present embodiment, 2000 rpm
m) It is determined whether or not it has reached or exceeded. If a negative determination is made in both steps 13 and 14 at this time, it is considered that the warm-up of the engine has not been completed, and it is determined that heating by the current-carrying heating element 2 of the glow plug is necessary, and the process proceeds to step 15.

If any one of the steps 13 and 14 is affirmatively determined, it is considered that the warm-up of the engine is completed or that the heating by the glow plug 1 is not necessary, and the step 1 is performed.
Proceed to 6.

When the operation proceeds to step 15, the glow relays 53 and 531 are kept on. In this state, the ignition and combustion of the fuel are continued by the heating action of the glow plug 1. Also, if you proceed to step 16,
The ECU 52 turns off the glow relays 53 and 531. Then, the ion relay 530 is turned on to detect the ion current.

Next, FIG. 6A is a current waveform diagram when an ion current generated during fuel combustion is observed using an oscilloscope. In the figure, the fuel injection timing (compression T
Immediately after DC), a waveform in which the voltage sharply rises is an ion current waveform due to fuel combustion, and point A corresponds to a combustion start position, that is, an ignition timing. Also, two peaks are observed in the ion current waveform. That is, in the early stage of combustion, the first peak B1 is observed by the active ions in the diffusion flame zone,
In the latter half of the combustion, the secondary
Mountain B2 is observed.

In this case, the ECU 52 detects the actual ignition timing from the first peak B1 of the ion current waveform,
Feedback control of the ignition timing is performed so as to eliminate the difference between the detected actual ignition timing and the target ignition timing. Further, the ECU 52 detects a combustion state such as abnormal combustion or misfire from the second peak B2 of the ion current waveform, and reflects the detection result in the fuel injection control. By reflecting the ion current in the fuel injection control of the engine in this way, it is possible to control the operating state of the engine finely.

Next, the ion detecting electrode 3 of the glow plug
When carbon (soot) generated by fuel combustion adheres, that is, when smoke is generated, as shown in FIG. 6 (B), the ion current is low before the fuel injection timing and rises thereafter. The phenomenon of going out occurs (compare (A) and (B) in FIG. 6). It should be noted that Ith in FIG. 6B represents a determination level (threshold value) of the peak value for determining whether the glow relays 53 and 531 are on by determining the smoldering state. Therefore, when such a smoldering phenomenon occurs, the glow relays 53 and 531 are turned on, the heating element 2 is heated, and the operation of burning off the attached carbon is performed.

FIG. 7 is a flow chart in which this carbon burning operation is performed by the ECU 52 in the circuit of FIG. That is, when the glow relays 53 and 531 are off in step 21 of FIG. 7, it is determined in step 22 whether the abnormal ion current (FIG. 6B) as described above is detected at the fuel injection timing. If no, the process proceeds to step 25 and the glow relays 53, 53
1 remains off.

On the other hand, when an abnormal ion current is detected, the routine proceeds to step 23, where the ion relay 530 is turned off.
Next, in step 24, the glow relays 53 and 531 are turned on to heat the energizing heating element 2 of the glow plug to burn off carbon.

As described above, in the glow plug of this embodiment, the heating element 2 and the lead wire 2 are placed inside the insulator 11.
1, 2 and an ion detection electrode 3 are provided, and these are integrally formed. Therefore, the glow operation (heating operation) by the electric heating element 2 and the ion current detection by the ion detection electrode 3 can be achieved by one glow plug. Also, the glow plug becomes compact.

Further, even when carbon adheres to the surface of the ion detecting electrode 3 and the glow plug, the carbon is burned off by heating the current-carrying heating element 2 as described above, and the ion detecting electrode 3 is made more normal. State. Therefore, the ion current can be detected with high accuracy.

Further, the electric heating element 2, the lead wires 21 and
2. Since the ion detection electrode 3 is provided inside the insulator 11, there is no corrosion such as oxidation due to combustion gas, and the durability is excellent. Further, since the tip of the insulator 11 has a hemispherical shape, it is possible to absorb a thermal shock in the combustion chamber.

Further, in this embodiment, the conductive layer 6 is provided on the surface of the insulator 11. The conductive layer 6 has an edge portion 61 at the upper end. Therefore, the exposed area of the ion detection electrode is increased, and the detection effect and responsiveness of the ion current can be improved by the edge effect of the edge portion 61.

That is, as shown in FIG. 8, in the detection of the ion current, the first rising angle D and the peak value P
is important. In the present embodiment, the conductive layer 6
Is provided, the rising angle D is large and a steep rising is obtained, and the peak value P is also very large.
Therefore, the ion detection accuracy is further improved, and the combustion state of the fuel can be more accurately controlled. In the present embodiment, the edge portion 61 is formed in a square shape. However, even when the edge portion 61 is rounded, substantially the same effect can be obtained as long as the edge portion is formed.

Embodiment 2 In this embodiment, an ion current detection test was performed to clarify the effect of the conductive layer in the glow plug shown in Embodiment 1. The prepared sample includes a glow plug (sample No. E1) having a cap-shaped large solid conductive layer 6 shown in Embodiment 1 and a dish-shaped small solid conductive layer 602 as shown in FIG. Glow plug (sample No. E2) and a glow plug without a conductive layer (sample No. C1). These are the same as the glow plug of the first embodiment except for the portions other than the conductive layer.

In the test, each glow plug was mounted on the same diesel engine, and the ion current was measured under the same conditions. Then, as shown in FIG.
The obtained ion current waveforms were compared, and the ion current detection accuracy and responsiveness were evaluated based on the rising angle D and the peak value P. Note that the larger the rising angle D and the larger the peak value P, the better the detection accuracy and responsiveness.

Table 1 shows the evaluation results. As is known from Table 1, the case where the conductive layers 6 and 602 are provided (E1, E
In 2), both the rising angle D and the peak value P were superior to the case without the conductive layer (C1). From this result, it can be seen that the provision of the conductive layers 6 and 602 significantly improves the detection accuracy and responsiveness of the ion current. E1 and E2 did not show much difference, but E1 having a slightly larger conductive layer area and a larger edge portion 61 was superior.

[0065]

[Table 1]

Embodiment 3 In this embodiment, as shown in FIGS. 10 to 12, the pattern of the conductive layer 6 (the shape of the exposed portion of the insulator 11) in the glow plug shown in Embodiment 1 was variously changed. Samples were prepared (Sample Nos. E3 to E5), and the influence of the pattern was tested. The overall shape of each conductive layer is the same as in the first embodiment.
The cap shape is the same as that of, and the sizes are all unified.
Each sample (E3 to E5) is the same as the first embodiment except for the conductive layer portion. The test method is described in Example 2 of the embodiment.
Is the same as

FIGS. 10 to 12 show modified patterns of the conductive layer. FIG. 9 shows a pattern of a conductive layer 603 having a grid pattern of E3. In the conductive layer 603, as shown in FIG. 13, the insulator 11 is exposed from between the meshes, and an edge portion 61 is provided at the boundary between each mesh and the insulator 11.

FIG. E4 conductive layer 604
Is shown. The conductive layer 604 is obtained by changing the shape of the exposed portion of the insulator 11 of E3 to a circular shape.
An edge portion 61 is provided at the boundary. Also,
FIG. The pattern of the conductive layer 605 of E5 is shown. The conductive layer 605 has an exposed portion of the insulator 11 in a wedge pattern shape, and has an edge portion 61 at a boundary portion thereof.
have. The shape of the main body 10 on which the conductive layers 604 and 605 are mounted is the same as that of FIG. 13 except for the pattern.

Using the glow plug having the conductive layers having various patterns as described above, the rising angle D and the peak value P of the ion current detection waveform were obtained in the same manner as in the second embodiment. The results are shown in Table 2 together with the results of E1. As can be seen from Table 2, the sample of this example (E3
To E5), the rising angle D and the peak value P were further improved as compared with E1 having no pattern. This is because, as shown in FIGS. 10 to 12, the conductive layer is provided with a pattern exposing the insulator 11, so that the edge portion 61 can be increased, and the above-described edge effect can be reliably exhibited. It is considered that

In this example, three types of conductive layers were evaluated as described above.
Conductive layers 606 and 607 having a pattern as shown in FIG.
Is provided, the same effects as those of E3 to E5 can be obtained.

[0071]

[Table 2]

Fourth Embodiment As shown in FIG. 16, this embodiment is a modification of the glow plug operating circuit (FIG. 4) of the first embodiment.
Battery 54 and DC power supply 51 are connected to one battery 5
Only 5 is replaced. Note that a constant current and constant voltage circuit 524 can be interposed between the ion current detection resistor 521 and the battery 55. In this case, there are effects of simplifying the circuit configuration and reducing costs.

The other points are the same as in the first embodiment. Also in this example, the same effect as in the first embodiment can be obtained. In particular, in this example, the interposition of the constant current / constant voltage circuit 524 prevents fluctuations in the voltage applied to the ion detection electrode caused when the glow plug generates heat even with a single battery, thereby achieving stable detection performance. The effect that it can be maintained can be obtained.

Embodiment 5 As shown in FIG. 17, in this embodiment, the heating element 2 and the ion detection electrode 3 in Embodiment 1 are separated from each other, and they are electrically insulated from each other. This is an example of buried inside. In addition, the tip of the main body 10 has the first embodiment.
A cap-shaped conductive layer 6 similar to that described above is provided. Other configurations are the same as those of the first embodiment. Also in the case of this example, the same operation and effect as in the first embodiment can be obtained.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view of a glow plug main body according to a first embodiment, and FIG. 1B is a cross-sectional view taken along line AA of FIG.

FIG. 2 is an overall explanatory diagram of a glow plug according to the first embodiment.

FIG. 3 is an explanatory diagram of a method for manufacturing a glow plug body according to the first embodiment.

FIG. 4 is a glow plug operation circuit diagram according to the first embodiment.

FIG. 5 is a flowchart of the glow plug operation system according to the first embodiment when the glow plug is started.

FIG. 6 is a diagram showing (A) an ion current at the time of normal operation and (B) an ion current at the time of smoking in the first embodiment.

FIG. 7 is a flowchart of smoldering determination in the first embodiment.

FIG. 8 is an explanatory diagram showing important points at the time of ion current detection in the first embodiment. FIG.

9A is a cross-sectional view and FIG. 9B is a bottom view showing a state of disposing conductive layers in the second embodiment.

FIG. 10 is an explanatory view showing a pattern of a conductive layer in a third embodiment.

FIG. 11 is an explanatory view showing a pattern of a conductive layer in a third embodiment.

FIG. 12 is an explanatory view showing a pattern of a conductive layer in a third embodiment.

FIG. 13 is an explanatory diagram showing an arrangement state of a conductive layer in a third embodiment.

FIG. 14 is an explanatory view showing a pattern of a conductive layer in a third embodiment.

FIG. 15 is an explanatory view showing a pattern of a conductive layer according to the third embodiment.

FIG. 16 is a glow plug operation circuit diagram according to a fourth embodiment.

17A is a cross-sectional view of a glow plug body according to a fifth embodiment, and FIG.

[Explanation of symbols]

 1. . . Glow plug, 10. . . Body, 11. . . Insulator, 2. . . Current-carrying heating element, 21, 22,. . . Lead wire, 3. . . 3. electrode for ion detection, . . Housing, 45. . . Cylinder head, 451. . . Swirl chamber, 6,602-606. . . Conductive layer, 61. . . Edge part,

Claims (6)

[Claims] 1. A glow plug comprising a housing and a main body supported in the housing, wherein the main body comprises:
An insulator, a current-carrying heating element provided inside the insulator, and a pair of lead wires electrically connected to both ends of the current-carrying heating element and led out of the insulator; An ion detection electrode for detecting an ionization state in the flame, and an ion detection electrode provided on the surface of the insulator so as to cover an exposed portion of the ion detection electrode from the insulator; A glow plug, further comprising a conductive layer electrically connected to the ion detection electrode. 2. The glow plug according to claim 1, wherein the conductive layer has an edge portion formed by partially exposing the insulator. 3. The glow plug according to claim 2, wherein said edge portion is angular. 4. The method according to claim 1, wherein:
The glow plug, wherein the conductive layer has a mesh structure, and a surface of the insulator is exposed between the meshes. 5. The method according to claim 1, wherein:
The said conductive layer is a metal or conductive ceramic, The glow plug characterized by the above-mentioned. 6. The method according to claim 1, wherein:
A glow plug, wherein the conductive layer has a thickness of 1 to 20 μm.