JPH1089226A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug to prevent the occurrence of a problem on adhesion of carbon, detect an ion current with high precision, prevent the occurrence of damage, such as a crack, be excellent in durability, and facilitate manufacture. SOLUTION: In a glow plug 1 comprising a housing; and a body 10 supported in the housing, the body 10 comprises an insulating body 11; an energization heat generating body 2, arranged at the internal part of the insulating body 11; a pair of lead wires 21 and 22 electrically connected to the two end parts of the energization heat generating body 2 and led out to the external part of the insulation body; and an electrode 3 for detecting ion to detect an ionized state in flame. The electrode 3 for detecting ion has at least its tip part 30 covered with an insulating porous layer 38 having a communication hole communicated with flame.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow plug for promoting ignition and combustion of fuel, and a method for manufacturing the same.

[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. In addition, since the ion detection electrode supported at the tip of the glow plug is exposed to a high-temperature flame, stress concentration is likely to occur near the ion detection electrode, which may cause cracks or other damage to the ceramic glow plug. There is also.

The present invention has been made in view of the above problems, has no problem of carbon adhesion, can accurately detect an ion current, has no damage such as cracks, has excellent durability, and has excellent manufacturing capability. An object is to provide an easy glow plug and a manufacturing method thereof.

[0009]

According to a first aspect of the present invention, there is provided a glow plug comprising a housing and a main body supported in the housing, wherein the main body includes an insulator, and a heat-generating heater provided inside the insulator. A body, a pair of lead wires electrically connected to both ends of the current-carrying heating element and led out of the insulator, and an ion detection electrode for detecting the state of ionization in the flame, and The glow plug is characterized in that at least a tip of the ion detection electrode is covered with an insulating porous layer having a communication hole communicating with the flame.

What is most notable in the present invention is that an electric heating element, a lead wire, and an ion detection electrode are disposed inside the insulator, and at least the tip of the ion detection electrode is the above-described electrode. That is, it is covered with the insulating porous layer.

The insulating porous layer has a communication hole communicating from the surface of the ion detection electrode to the inside of the flame, and is electrically insulating. Such an insulating porous layer is made of, for example, Si ₃ N
₄ , manufactured by sintering an electrically insulating ceramic powder mainly composed of Al ₂ O ₃ , SiO ₂ or the like.

Next, when disposing the energizing heating element and the ion detecting electrode in the insulator, for example, as shown in the embodiment, the energizing heating element and the ion detecting electrode are prepared in advance. On the other hand, an insulator provided with grooves for burying them is prepared, and the heating element and the electrode for ion detection are buried in the grooves and integrally fired. These electric heating elements, ion detection electrodes, and insulators are manufactured using, for example, ceramic powder.

Next, the function and effect of the present invention will be described.
The glow plug of the present invention generates heat by passing an electric current through the above-mentioned current-carrying heating element, and the ignition thereof 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.

What is important here is that the tip of the ion detecting electrode is covered with the insulating porous layer, so that the ion detecting electrode is not directly exposed to the flame. Therefore, the electrode for ion detection does not cause stress concentration due to thermal shock due to a high-temperature flame, and does not cause damage such as cracks. In addition, since the insulating porous layer has the communication hole, the ion current flows between the ion detection electrode and the cylinder head through the communication hole, and is accurately detected.

As a result, the ion current can be accurately detected, and the information can be effectively used for combustion control. Further, since the glow plug is provided with an original heat generation function (glow function) and an ion current detection function, the structure can be made compact and inexpensive.

Further, since the current-carrying heating element is buried inside the insulator, it does not corrode due to a combustion flame, does not cause a decrease in resistance value, and does not cause a change in heat-generating characteristics. And it has excellent durability. That is, since the current-carrying heating element is not consumed by oxidation, its cross-sectional area is kept constant and its resistance value does not change. In addition, it is possible to avoid problems such as breakage of the current-carrying heating element due to thermal shock or the like in the combustion chamber.

[0017] In addition, carbon may adhere to the surface of the above-mentioned insulator due to fuel combustion, and the deposited carbon is caused by the heating operation of the current-carrying heating element (for example, the glow operation when the engine is started at a low temperature). Can be burned. Therefore, the ion current can be accurately detected over a long period of time.

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, the ion current can be detected with high accuracy, there is no damage such as cracks, the durability is excellent, and the production is easy.
A glow plug can be provided.

Next, it is preferable that the thickness of the insulating porous layer is 0.2 to 1.5 mm. If the thickness is less than 0.2 mm, there is a risk of damage such as cracks due to the thermal shock of the flame. On the other hand, if the thickness exceeds 1.5 mm, the thickness becomes large, so that stress concentration due to flame heat is likely to occur and cracks may occur.

Next, it is preferable that the insulating porous layer and the insulator are made of the same material. As a result, the bondability between the two is improved, and the coefficient of linear expansion of the two becomes the same, so that the thermal shock resistance is improved.

Next, as in the fourth aspect of the present invention, the electrode for ion detection can be used also as an electric heating element (FIG. 13). In this case, the insulating porous layer covers the current-carrying heating element (that is, the electrode for ion detection) at the tip of the main body of the glow plug.

The ion detecting electrode is made of MoSi.
₂ , conductive ceramic material containing WC, TiN, etc.,
Alternatively, it can be made of a high melting point metal such as W, Mo, and Ti. It is preferable that the tip of the insulator has a hemispherical shape. In this case, by removing the acute angle portion of the insulator, the turbulence of the combustion flame flow near the ion detector is suppressed, the detection performance is stabilized, and the concentration of thermal stress is suppressed, and the thermal shock resistance is improved. The effect of improving is obtained.

The communication holes formed in the insulating porous layer of the present invention may have any diameter as long as they are connected from the surface of the porous layer to the electrode surface. For example, when the tip of the glow plug of the present invention is immersed in a 50:50 aqueous alcohol solution of water and alcohol, and a voltage of, for example, 12 volts is applied between the tip and the aqueous solution, a communication hole through which current flows. Should be fine.

[0024]

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. Glow plug 1 of this example
Comprises a main body 10 and a housing 4 for holding the main body 10, as shown in FIG. 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 which is electrically insulated from the electric heating element 2 and is disposed inside the insulator 11 for detecting the state of ionization in the flame. The tip portion 30 of the ion detecting electrode 3 is covered with an insulating porous layer 38 having a communication hole 380 (FIG. 3) communicating with the flame, including the tip portion of the insulator 11. ing.

As shown in FIGS. 1 and 2, the main body 10 is provided within a metal housing 4 in a metal annular support 4.
1 and is fixed. 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. The other lead wire 22 is electrically connected to the housing 4 via the annular support 41. The upper end of the ion detection electrode 3 is electrically connected to the internal lead 33 via a conductive terminal 31 provided on the upper end of the insulator 11.

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 heating element 2, and the external lead wire 333 is electrically connected to the ion detecting electrode 3.

The other end of the heating element 2 is electrically connected to the housing 4 via the annular support 41 as described above (FIG. 1). The distal end (lower end) of the main body 10 is formed in a hemispherical shape as shown in FIG. 1, and the distal end 30 of the ion detection electrode 3 is exposed.

Next, a method of manufacturing the glow plug body 10 will be described with reference to FIGS. First, the main body 10 of the glow plug is, as shown in FIG.
1, an electric heating element 2 embedded therein, an electrode 3 for ion detection, and the insulating porous layer 38. Therefore, first, as shown in FIG.
U-shaped heating element 2 and rod-shaped electrode 3 for ion detection
Are prepared in advance.

On the other hand, as shown in FIG. 5, a substantially semicircular lower part 111 and a substantially plate-shaped middle part 1 for forming the insulator 11 are formed.
12 and the substantially semicircular upper part 113 are prepared in advance using insulating ceramic powder. U-shaped grooves 115 and 116 are formed in the upper surface of the lower portion 111 and the lower surface of the middle portion 112 for receiving the electric heating element 2.

On the upper surface of the middle portion 112 and on the lower surface of the lower portion 113, bar-shaped grooves 117 and 118 for receiving the ion detecting electrodes 3 are formed. Then, the energizing heating element 2 is inserted into the U-shaped grooves 115, 116, and the rod-shaped grooves 117,
The ion detection electrode 3 is put in 118, and these are laminated. At this time, the lead wire 21 was
22 is connected.

As a result, a laminate is obtained as shown in the upper part of FIG. Therefore, the tip 18 of the laminate is
The disk-shaped insulating porous layer 382 previously formed
Are bonded with an adhesive. Next, these are heated and sintered to form an integrally sintered body. Further, as shown in FIG. 6 (B), the lower part of the integrated sintered body is ground (dotted line in the lower part of FIG. 6) to form a hemispherical shape. Thus, the glow plug main body 10 shown in FIG. 1 is obtained.

Next, as shown in FIG. 7, the glow plug 1 constituted by the main body 10 and the housing 4 as described above is formed 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 a metal cylinder head 45. Further, the cylinder head 45, the housing 4, the annular support 41, and the lead wire 22 of the main body 10 (FIG. 1)
Is connected to the other end of the current-carrying heating element 2. Thus, a circuit for heating the energizing heating element 2 is formed.

The external lead 333 of the ion detecting electrode 3 is connected to an ion current detecting resistor 521,
Is connected to the cylinder head 45 via the. Also,
The ionic current detecting resistor 521 is provided with a potentiometer 522 for detecting an ionic current.
(Electronic control device) 52. In addition, ECU
52 includes a glow relay 53, 531, a coolant temperature sensor 525 for the engine coolant, and an engine speed sensor 52.
6 are connected.

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 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 fuel is burning, ions are generated as described above, and the ion current is detected by the ion detection electrode 3, the ion current detection resistor 521, and the potentiometer 522. That is, the glow plug body 1
A voltage is applied between the ion detection electrode 3 and the cylinder head 45 by a 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 at 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 the 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 and 531 will be described below with reference to the flowchart of FIG. This drawing 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, in 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 in 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 of steps 13 and 14 is affirmatively determined, it is determined that the warming-up of the engine has been completed or that heating by the glow plug 1 is not necessary.
Proceed to 6.

When the process 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.

Next, FIG. 9A 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. 9 (B), the ion current is low before the fuel injection timing and rises thereafter. The phenomenon of going up occurs (compare (A) and (B) of FIG. 9). It should be noted that Ith in FIG. 9B represents a determination level (threshold value) of the peak value for determining whether or not the glow relays 53 and 531 are to be turned on and whether or not the glow relays 53 and 531 are to be turned on. 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.

Next, FIG. 10 is a flowchart 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 in the off state in step 21 in FIG. 9, it is determined in step 22 whether the abnormal ion current (FIG. 9B) as described above is detected at the fuel injection timing. If no, the process proceeds to step 24, where the glow relay 5
3,531 is kept off. On the other hand, when an abnormal ion current is detected, the process proceeds to step 23, where the glow relays 53 and 531 are turned on, and the heating element 2 of the glow plug is heated 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 and 22 are formed, and an ion detection electrode 3 is provided inside the insulator 11, 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.

Even when carbon adheres to the surface of the glow plug body 10, that is, the surface of the insulator 11, the heating of the current-carrying heating element 2 near the ion detecting electrode 3 can be performed by heating. The carbon is burned off, and the ion current detection can be returned to the normal state. Therefore, ions can be accurately detected through the communication holes 380 (FIG. 3) of the insulating porous layer 38.

It is important that the tip 30 of the ion detecting electrode 3 is covered with the insulating porous layer 38 (FIG. 3).
Is not directly exposed to the flame. Therefore, the ion detecting electrode 3 does not generate stress concentration due to thermal shock due to a high-temperature flame, and does not cause damage such as cracks. Further, since the insulating porous layer 38 has the communication hole 380, the ions flow between the ion detection electrode 3 and the cylinder head 45 through the communication hole 380, and are accurately detected as an ion current.

Further, since the insulator 11, the electric heating element 2, the lead wires 21, 22, the ion detecting electrode 3, and the insulating porous layer 38 are integrally formed, the structure is simple.
Further, since the electric heating element 2 and the lead wires 21 and 22 and the ion detection electrode 3 are provided inside the insulator 11, there is no corrosion such as oxidation due to combustion gas and the durability is excellent.
The tip of the insulator 11 has a hemispherical shape (FIGS. 1 to 3).
Therefore, thermal shock in the combustion chamber can be absorbed.

Second Embodiment Next, a specific example of the glow plug body shown in the first embodiment is shown in Table 1 together with a comparative example. First, the conductive heating element is composed of a conductive MoSi ₂ (molybdenum disilicide) powder having a small particle size, insulating Si ₃ N ₄ (silicon nitride) having a large particle size, and Y ₂ O _{3 serving as} a sintering aid. And an organic binder to form a U-shape (FIG. 4A). Also, the ion detection electrode was formed into a rod shape using the same material (FIG. 4B).

Next, the insulator is made of Si ₃ N ₄ having a small particle size.
And MoSi ₂ , Y ₂ O _3, and an organic binder having substantially the same particle size, as shown in FIG.
Molded into the middle part 112 and the lower part 113, respectively. On the other hand, the insulating porous layer 38 is made of the same material as that for the insulator 11 except that the amount of the organic binder is increased.
It was molded into 2.

Then, these were laminated as described above, and as shown in FIG. 6, the plate-shaped body 382 of the insulating porous layer was bonded to the tip of the laminated body via an adhesive. Then, after laminating the organic binder at 450 ° C., the laminate of these formed bodies was pressure-sintered at 1750 ° C. for 60 minutes. Further, the tip of the glow plug was ground into a hemispherical shape to obtain a glow plug body shown in FIG.

The thickness of the insulating porous layer 38 in the glow plug main body 10 was variously changed as shown in Table 1. The thickness of the insulating porous layer 38 showed the maximum thickness because the tip was hemispherical.

Next, the glow plug is replaced with the first embodiment.
As shown in FIG. 7, the head was mounted on a cylinder head 45 of a diesel engine. Then, after energizing the heating element of the glow plug and heating it to 1200 ° C., the engine is started,
After idling for one minute and stopping the engine for one minute, the engine test was repeated 20,000 times and 30,000 times to repeat the above-described energization, start and stop. Then, damages such as cracks in the tip of the electrode for ion detection and the surrounding insulator were observed. Table 1 shows the results.
Shown in

As can be seen from Table 1, the sample (No. 1) having no insulating porous layer 38 had chipping due to cracks in the 20,000 times test. In addition, of those provided with an insulating porous layer, the thickness is 0.1 and 1.6 m.
m (Sample Nos. 2 and 7) showed damage such as cracks after 30,000 tests. Since the above test was performed under severe conditions, the sample No. Samples Nos. 2 and 7 have almost no problem in practical use. Those having 3 to 6 have excellent durability.

[0060]

[Table 1]

Third Embodiment As shown in FIG. 11, this embodiment is a modification of the glow plug operation circuit (FIG. 7) 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, by interposing the constant current / constant voltage circuit 524, even with one battery, the fluctuation of the voltage applied to the ion electrode caused at the time of heat generation of the glow plug can be prevented, and the stable detection performance can be maintained. The effect described above can be obtained.

Fourth Embodiment As shown in FIG. 12, in the glow plug body 10, an ion detection electrode 3 is integrally provided at the lower end of the U-shaped current-carrying heating element 2, as shown in FIG. 3 tip 3
This is an example in which the same insulating porous layer 38 as that of the first embodiment is provided on the first embodiment. According to this embodiment, the structure of the glow plug is simplified because the ion detection electrode 3 is provided at the tip of the energizing heating element 2. Other configurations are the same as those of the first embodiment, and the same effects as those of the first embodiment can be obtained.

Fifth Embodiment As shown in FIG. 13, this embodiment is an example in which a U-shaped current-carrying heating element 2 is also used as an ion detection electrode 3. In this example, the front end (U-shaped lower end) and the lower side surface of the ion detection electrode 3 are covered with the insulating porous layer 38. According to this example, the structure is simple because the electrode for ion detection and the electric heating element are also used. The operation circuit of the glow plug of this example is as shown in the sixth embodiment. Other configurations are the same as those of the first embodiment, and the same effects as those of the first embodiment can be obtained.

Embodiment 6 As shown in FIGS. 14 and 15, this embodiment is a case where the energizing heating element and the ion detection electrode shown in Embodiments 4 and 5 are integrated. FIG. 2 shows an overall cross-sectional view of a glow plug main body and a glow plug operation circuit.
That is, as shown in FIG. 14, in the case of the above-mentioned integration, the lead wire 22 provided on the electric heating element 2 is connected to the terminal portion 31 provided on the upper end of the insulator 11.

The glow plug thus configured is similar to that of the first embodiment shown in FIG.
Attach to 5. Further, in the case of this example, since the energizing heating element 2 and the ion detecting electrode 3 are integrated, the operation circuit of the glow plug has the configuration shown in FIG.

When the energizing heating element 2 is to generate heat, the ion relay 530 is turned off and the glow relays 53 and 531 are turned on, as shown in FIG. On the other hand, when the ion current is detected by the ion detection electrode 3, the ion relay 530 is turned on and the glow relay 53 is turned on.
And 531 are off. Thereby, the same effect as that of the first embodiment can be obtained. Other configurations are the same as those of the first embodiment.

[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 an insulating porous layer in the first embodiment.

FIG. 4 shows (A) an electric heating element according to the first embodiment;
(B) The perspective view of the electrode for ion detection.

FIG. 5 is an explanatory diagram of the method for manufacturing the glow plug body in the first embodiment.

FIG. 6 is an explanatory view of the method for manufacturing the glow plug main body, following FIG. 5;

FIG. 7 is a glow plug operation circuit diagram in the first embodiment.

FIG. 8 is a flowchart of the glow plug operation system according to the first embodiment when the glow plug is started.

FIGS. 9A and 9B are diagrams 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. 10 is a flowchart for determining smoking in the first embodiment.

FIG. 11 is a glow plug operation circuit diagram according to a third embodiment.

FIG. 12 is a sectional view of a glow plug body according to a fourth embodiment.

FIG. 13 is a sectional view of a glow plug body according to a fifth embodiment.

14A is a cross-sectional view of a glow plug body according to a sixth embodiment, and FIG. 14B is a cross-sectional view taken along the line BB of FIG.

FIG. 15 is a glow plug operation circuit diagram according to a sixth embodiment.

[Explanation of symbols]

 1. . . Glow plug, 10. . . Body, 11. . . Insulator, 2. . . Current-carrying heating element, 21, 22,. . . Lead wire, 3. . . Electrode for ion detection, 30. . . Tip, 38. . . 3. an insulating porous layer; . . Housing, 45. . . Cylinder head, 451. . . Swirl chamber,

Claims (4)

[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,
A pair of lead wires electrically connected to both ends of the current-carrying heating element and led out of the insulator; and an ion detection electrode for detecting the state of ionization in the flame.
A glow plug, wherein at least the tip of the ion detection electrode is covered with an insulating porous layer having a communication hole communicating with the flame. 2. The glow plug according to claim 1, wherein said insulating porous layer has a thickness of 0.2 to 1.5 mm. 3. The glow plug according to claim 1, wherein the insulating porous layer and the insulator are formed of the same material. 4. The method according to claim 1, wherein:
A glow plug, wherein the ion detection electrode is also used as the electric heating element.