JPH10110950A - Glow plug and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug free from deposition of carbon, which is capable of precisely sensing ion current and further has superior durability. SOLUTION: A glow plug comprised of a housing 4 and a main body 10 supported within the housing is constructed such that the main body 10 is comprised of a rod-like insulator 11, an electrical energized heater 2 printed and formed within the rod-like insulator member at its one end, a pair of lead lines 21, 22 electrically connected to both ends of the electrical energized heater 2 and fed out to the other end of the rod-like insulator member, and an ion sensing electrode 3 electrically insulated against the electrical energized heater 2 and arranged within the rod-like insulator 11 so as to detect a state of ionization in the 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.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a glow plug which has no problem of carbon adhesion, can detect an ion current with high accuracy, has excellent durability, and a method of manufacturing the same. Is what you do.

[0009]

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 is formed by printing a rod-shaped insulator and inside the rod-shaped insulator. An energizing heating element and a pair of lead wires electrically connected to both ends of the energizing heating element and led out of the rod-shaped insulator; and disposed inside the rod-shaped insulator electrically insulated from the energizing heating element. The glow plug comprises an ion detection electrode for detecting an ionization state in the flame.

In the present invention, the most remarkable thing is that a current-carrying heating element and a lead wire are printed and formed inside the rod-shaped insulator, and the inside of the rod-shaped insulator is electrically insulated from the current-carrying heating element. Is provided with an ion detection electrode. 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.

The ion detecting 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.

Further, since the current-carrying heating element is buried in the rod-shaped insulator in a printed state, it does not corrode due to a combustion flame, and may cause a decrease in resistance value and a change in heat generation characteristics. Therefore, high heat generation performance can be exhibited over a long period of time. 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.

[0014] In addition, carbon may adhere to the surface of the ion detection electrode in the course of fuel combustion, and the deposited carbon is used to heat the current-carrying heating element (for example, glow operation when the engine is started at a low temperature). ). Therefore, the ion current can be accurately detected over a long period of time.

Further, in the present invention, the electric heating element is provided by printing inside the rod-shaped insulator. As an example of such printing, as will be described later, for example, a conductive material is formed into a desired shape by screen printing, pad printing, hot stamping, or the like on the surface of a green body formed of a ceramic material for forming a rod-shaped insulator. This is performed by printing a conductive heating element made of a conductive material and a lead wire. Next, the formed form is wound and then fired. As a result, a bar-shaped insulator containing the printed heating element and the lead wire can be obtained.

On the other hand, with regard to the arrangement of the ion detecting electrode, for example, when the above-mentioned formed body is wound, a hollow portion is provided in the center thereof along the axial direction, and before or after the above-mentioned sintering, A rod-shaped electrode for ion detection is inserted and fixed in the hollow part via a material.

As described above, in the present invention, the electric heating elements and the lead wires are formed by printing inside the rod-shaped insulator. Therefore, the current-carrying heating element and the lead wire should be 0.005
The glow plug can be disposed in the glow plug in a thin layer state of about 0.02 mm, and the glow plug becomes compact. Also,
The current-carrying heating element and the lead wires are not exposed to the fuel flame, and therefore have excellent durability.

Further, the glow plug of the present invention has a simple structure since the current-generating heating element, the lead wire, and the electrode for ion detection are integrally provided inside the rod-shaped insulator. Therefore, according to the present invention, it is possible to provide a glow plug which has no problem of carbon adhesion, can detect an ion current with high accuracy, and has excellent durability.

Next, according to a second aspect of the present invention, in a glow plug comprising a housing and a main body supported in the housing, the main body includes an electrically insulating middle shaft having a hollow portion and an outer periphery of the middle shaft. A rod-shaped insulator composed of an insulating substrate covered with a conductive material, and a rod-shaped insulator formed by printing between the center shaft and the insulating substrate inside the rod-shaped insulator from both ends of the current-carrying heating element. It has a lead wire led out of the body and an ion detection electrode for detecting the state of ionization in the flame, which is electrically insulated from the current-carrying heating element and inserted and fixed in the hollow portion of the center shaft. There is a glow plug characterized by the following.

In this case, since the rod-shaped insulator is constituted by the center shaft and the insulating substrate, its manufacture is easy.
Further, the same effects as those of the first aspect can be obtained.

Next, as in the third aspect of the present invention, it is preferable that the electric heating element is printed on the inner surface of the insulating substrate. In this case, it is easy to manufacture because the energizing heating element and the lead wires are printed and formed on a sheet-like insulating substrate in advance and wound around a center shaft. next,
As in the invention of claim 4, it is preferable that the tip of the ion detection electrode is exposed at the tip of the rod-shaped insulator so as to be exposed to the flame. In this case, the effect of improving the responsiveness of ion current detection and the detection accuracy (S / N ratio) can be obtained. Next, as in the invention of claim 5, the electrode for ion detection is one or two of MoSi ₂ , WC and TiN.
It can be made of more than one kind of conductive ceramic material. In this case, the heat resistance is improved, and the coefficient of expansion with the insulator can be easily adjusted and combined, so that the effect of improving the thermal shock resistance can be obtained.

Next, as in the sixth aspect of the present invention, the ion detecting electrode can be made of one or more refractory metals of W, Mo, and Ti. In this case, since the material can be used in the form of a line, the effect of reducing costs relating to the material, processing, and assembly can be obtained.

Next, one or more of Pt, Ir, Rh, Ru, Pd may be provided on the exposed portion of the ion detecting electrode exposed from the rod-shaped insulator. Is preferably provided. In this case,
The effect of improving the wear resistance and oxidation resistance of the detection electrode is obtained. Next, the tip of the rod-shaped insulator preferably has a hemispherical shape.
In this case, by removing the sharp edge of the rod-shaped insulator, the turbulence of the combustion flame flow near the ion detector is suppressed, the detection performance is stabilized, the concentration of thermal stress is suppressed, and the thermal shock resistance is reduced. Is obtained.

Next, as in the ninth aspect of the present invention, in manufacturing the glow plug of the second aspect, a center shaft formed body made of an electrically insulating ceramic material and having a hollow portion is prepared. The electrode for ion detection is inserted into the part, and the energizing heating element and the lead wire are printed on the surface of the formed body of the insulating substrate made of an electrically insulating ceramic material, and then formed on the printed surface of the insulating substrate. There is a method for manufacturing a glow plug, which comprises winding the insulating substrate around the outer periphery of the center shaft while placing the formed shape of the center shaft, and then heating them to fire the center shaft and the insulating substrate.

In this case, the above-mentioned claim 1 and claim 2
The glow plug having the effects described in (1) and (2) can be easily manufactured.

[0026]

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 FIGS. 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 comprises a rod-shaped insulator 1
1, a current-carrying heating element 2 formed on one end of the rod-shaped insulator 11 by printing, and electrically connected to both ends of the current-carrying heating element 2 and led to the other end of the rod-shaped insulator. And a pair of lead wires 21 and 22.

Further, there is provided an ion detection electrode 3 which is electrically insulated from the electric heating element 2 and disposed inside the rod-shaped insulator 11 for detecting the state of ionization in the flame. The ion detecting electrode 3 is provided at the center of the rod-shaped insulator in the diameter direction.

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. The one lead wire 21 of the current-carrying heating element 2 rises inside the rod-shaped insulator 11 and is electrically connected to the internal lead wire 231 via a conductive terminal portion 23 provided on the side surface of the main body 10. It is connected.
The other lead wire 22 is electrically connected to the housing 4 via the annular support 41. The upper part of the ion detecting electrode 3 is connected to the inner lead wire 3 via a conductive terminal part 31 provided at the upper end of the rod-shaped insulator 11.
3 is electrically connected.

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 FIG. First, to explain the outline, it is made of an electrically insulating ceramic material,
A formed body of the central shaft 13 having the hollow portion 131 is prepared, and the ion detection electrode 3 is inserted into the hollow portion 131. On the other hand, the energizing heating element and the lead wires are formed by printing on the surface of the sheet 15 of the formed body of the insulating substrate made of an electrically insulating ceramic material, and then the formed body of the center shaft 13 is formed on the printed surface of the insulating substrate. Is placed and the insulating substrate is wound around the outer periphery of the center shaft. Thereafter, these are heated to bake the center shaft and the insulating substrate.

That is, as shown in FIG. 3, first, the center shaft 13 is mixed with a raw material composed of a ceramic material, a resin binder and the like (FIG. 3A), and extruded (FIG. 3A).
(B)) Then, a cylindrical body having a hollow body 131 penetrating in the axial direction is produced. The conductive rod-shaped ion detection electrode 3 is inserted into the hollow portion 131 of the center shaft 13 (FIG. 3C).

On the other hand, with respect to the insulating substrate, first, a raw material composed of a ceramic material, a resin binder and the like is mixed (FIG. 3D) to form a thin sheet 15 (FIG. 3).
(E)). Next, a through hole for forming a terminal portion is formed in the sheet 15 (FIG. 3F), and then the conductive heating element is formed on the front side of the sheet 15 by screen printing using a conductive paste for the conductive element. The portion 20 is formed by printing (FIG. 3G). Similarly, the lead wire portion 21
0, 220 to be connected to the through hole 151,
Print formation (FIG. 3 (h)).

Further, on the back surface of the sheet 15, a terminal portion 230 is formed by printing with a conductive paste so as to be electrically connected to the through hole 151 (FIG. 3 (i)).
Next, a coating material comprising a ceramic material and a resin binder is coated and printed on the front side of the sheet 15 (FIG. 3 (j)). This is to eliminate the step between the print-formed portion such as the energized heating element portion 20 and the sheet surface and to flatten it, and to improve the adhesion between the sheet 15 and the center shaft 13 during the next winding.

Next, the center shaft 13 into which the ion detecting electrode 3 is inserted is placed on the surface of the sheet 15 on which the energized heating element portion 20 and the like are formed, and the sheet 15 is wound around the center shaft 13. Wrap (Fig. 3
(K)). Next, degreasing is performed by preheating, main heating is performed, and the sheet 15 made of a ceramic material and the central shaft 13 are integrally fired (FIG. 3 (l)). At this time,
The sheet 15 and the center shaft 13 are strongly adhered to each other due to shrinkage during firing. The electrode 3 for ion detection is
Due to the shrinkage of baking of No. 3, it is strongly adhered and joined.

Next, the terminal portion 230 is plated with Cu and then with Ni (FIG. 3 (m)). Next, the internal lead wire 231 is assembled to the terminal portion 230 by brazing (FIG. 3 (n)), and the surface thereof is plated with Ni (FIG. 3 (o)). The tip of the rod-shaped insulator 11 is ground to a spherical state as shown in FIG. Thus, the glow plug main body 10 shown in FIG. 1 is obtained.

Next, with respect to the glow plug body 10,
For example, the center shaft 13 has an outer diameter of 3.9.
mm, the inner diameter forming the hollow portion 131 was 0.7 mm. The sheet 15 has a thickness of 0.3 mm and a width of 1 mm.
It was 1.5 mm and length 54 mm. The outer diameter at the time of the winding was 4.5 mm, and the diameter of the ion detecting electrode 3 inserted into the hollow portion 131 was 0.7 mm.

The material of the center shaft 13 is Si ₃ N ₄
(Silicon nitride) powder 63% (weight ratio), MoSi ₂ (molybdenum disilicide) powder 18%, Y ₂ O ₃ (yttria) powder 4%, Al ₂ O ₃ (alumina) powder 3%
12% composite binder containing paraffin wax as a main component
Were used in a mixture. The material of the sheet 15 is Si
₃ N ₄ (silicon nitride) powder 70% (weight ratio) and MoSi
₂ (Molybdenum disilicide) powder 20% and paraffin WA
It was mixed with 10% of a composite binder containing X as a main component.

As the material of the electric heating element portion 20, a paste made of W (tungsten) and Re (rhenium) was used. Also, the lead wire portions 210, 22
The W (tungsten) paste was used as the conductive paste on which the terminal portions 230 were formed by printing. The material of the ion detecting electrode is made of MoSi ₂ (molybdenum disilicide).

Next, the above-mentioned wound material (FIG. 3) was fired at 1700 to 1800 ° C. for 2 to 4 hours in an argon or nitrogen atmosphere. Due to this firing, the outer diameter of the above-mentioned central shaft is changed from 3.9 to 3.1 mm, the outer diameter of the rolled material (rod-shaped insulator) is changed from 4.5 mm to 3.6 mm, and the ion detecting electrode is set to 0.1 mm. It shrank from 7 mm to 0.6 mm. Further, the surface of the exposed portion 30 (FIG. 1) at the tip of the ion detecting electrode 3 was coated with Pt.

Next, as shown in FIG. 4, the glow plug 1 composed of the main body 10 and the housing 4 is formed by screwing the male thread of the housing 4 into the cylinder head 45 of the engine as shown in FIG. 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, glow relay 53, and 12 volt battery 54
Is connected to a metal cylinder head 45 via a. Further, via the cylinder head 45, the housing 4, the annular support 41, and the lead wire 22 (FIG. 1) of 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 external lead 333 of the ion detection electrode 3 is connected to an ion current detection resistor 521 and a DC power supply 51.
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
The glow relay 53, the engine coolant temperature sensor 525, and the engine speed sensor 526 are connected to 52.

When using the glow plug 1 shown in FIG.
The glow relay 53 is 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 closed.
Is energized and generates heat. Therefore, the glow plug 1 is in a heating state, the vortex chamber 451 is heated, and the ignition temperature rises. 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, 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.

Therefore, 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 detection 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 energizing 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 relay 53 is in an on state, and the energized heating element 2 is maintained in a heated state.

The on / off switching process of the glow relay 53 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 process of FIG.
First, at step 11, it is determined whether or not the engine has been warmed up and the glow relay 53 is off. At the beginning of the engine start, a negative determination is made in step 11, and the ECU 52 reads the water temperature Tw and the engine speed Ne in the subsequent 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 one of the steps 13 and 14 is affirmatively determined, it is determined that the warm-up of the engine is completed or that the heating by the glow plug 1 is unnecessary, and the step 1 is performed.
Proceed to 6.

When the operation proceeds to step 15, the glow relay 53 is kept on. In this state, the ignition and combustion of the fuel are continued by the heating action of the glow plug 1. When the process proceeds to step 16, the ECU 52
Turns off the glow relay 53.

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. 6 (A) represents a determination level (threshold) of the peak value for determining whether or not the glow relay 53 is ON by determining the smoldering state. Therefore, when such a smoldering phenomenon occurs, the glow relay 53 is turned on and the heating element 2 is turned on.
Is heated to burn off the attached carbon.

FIG. 7 is a flow chart in which the carbon burn-off operation is performed by the ECU 52 in the circuit of FIG. That is, when the glow relay 53 is in the off state in step 21 of FIG.
In, it is determined whether or not the abnormal ion current (FIG. 6B) as described above is detected at the fuel injection timing. If not,
Proceeding to step 24, the glow relay 53 remains off. On the other hand, when an abnormal ion current is detected, the process proceeds to step 23, where the glow relay 53 is turned on, and the heating element 2 of the glow plug is heated to burn out carbon.

As described above, in the glow plug of this embodiment, the heating element 2 and the lead wires 21 and 22 are printed and formed inside the rod-shaped insulator 11, and the ion detecting electrode is formed inside the rod-shaped insulator 11. 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.

Even when carbon adheres to the electrode 3 for ion detection, the carbon is burned off by heating the current-carrying heating element 2 near the electrode 3 for ion detection. Can be brought into a normal state. Therefore, the ion current can be detected with high accuracy.

The above-mentioned electric heating element 2, lead wire 21,
Since the print 22 is formed by printing, its thickness is small, and the glow plug body can be made compact. Further, since the rod-shaped insulator 11, the electric heating element 2, the lead wires 21, 22 and the ion detecting electrode 3 are integrally formed, the configuration 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 rod-shaped insulator 11, there is no corrosion such as oxidation due to combustion gas and the durability is excellent.

In the glow plug body 10 of this embodiment, as shown in FIG. 3, an electric heating element and a lead wire are formed on an insulating substrate sheet 15 by printing, and the ion detecting electrode 3 is formed thereon. It is manufactured by placing the inserted central shaft 13, winding and firing. Therefore, manufacture of the glow plug body is easy. Further, since the tip of the rod-shaped insulator 11 has a hemispherical shape, it is possible to absorb a thermal shock in the combustion chamber.

Further, the tip portion 30 of the ion detecting electrode 3
Is exposed so as to come into contact with the combustion gas (FIG. 1), and the exposed portion is coated with a noble metal such as Pt. Therefore, the generation of an insulator on the surface of the electrode for ion detection due to oxidation or the like is suppressed, the conductivity of the electrode or the initial resistance value is secured, and there is an effect of preventing deterioration of detection accuracy. Further, the ion detection electrode 3 is disposed at the center of the rod-shaped insulator 11 in the diameter direction. Therefore, ion currents in all directions in the combustion chamber can be detected with high accuracy.

The rod-shaped insulator is made of Si ₃ N ₄ ,
_{Al 2 O 3, Si-Al} -O-N may also be used (SiAlON). In addition, W, Mo, Re, W / M may be used as the conductive paste for printing and forming an electric heating element.
o, WC, WC / Re or W / Re, and a paste composed of a resin. In the above description, an example is shown in which the ion detection electrode 3 is inserted into the hollow portion 131 of the center shaft 13 of the formed body, and then the whole is fired (FIG. 3). It is also possible to obtain a method of inserting into the center shaft and fixing with an adhesive (see FIG. 3, lower right).

Embodiment 2 As shown in FIG. 8, the present embodiment is a modification of the glow plug operating circuit (FIG. 4) of Embodiment 1, in which the battery 54 and DC power supply 51 of Embodiment 1 are connected. One battery 55
Only in place. 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 3 In this embodiment, as shown in FIG. 9, one lead wire 220 of the current-carrying heating element 2 in the glow plug main body 10 is connected to a terminal portion 31 provided at the upper end of the rod-shaped insulator 11. In this example, the terminal portions of the lead wire 220 and the ion detection electrode 3 are shared. In this case, the circuit for heating the current-carrying heating element 2 and the ion current detection circuit are controlled by a command signal from the ECU 52.
The circuit configuration is such that the switch is switched and the operating state is always connected to either the energized heating element heating state or the ion current detecting state. Others are the same as the first embodiment, and the same effects as the first embodiment can be obtained.

In this embodiment, since the terminal portion 31 is shared, the structure is simple. Also, in this example, in the ion current detection state, the current-carrying heating element itself also acts on the ion detection electrode, so that the area of the ion detection electrode can be substantially expanded, and a wider range of ion detection can be performed, and the detection accuracy can be improved. The effect of improvement is obtained.

[Brief description of the drawings]

1A is a cross-sectional view of a glow plug main body according to a first embodiment; 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 a glow plug operation circuit diagram according to a second embodiment.

9A is a cross-sectional view of a glow plug body according to a third embodiment, and FIG. 9B is a cross-sectional view taken along line BB of FIG. 9A.

[Explanation of symbols]

 1. . . Glow plug, 10. . . Body, 11. . . 12. rod-shaped insulator; . . Center axis, 15. . . Sheet, 2. . . Electric heating element, 21, 22, 220. . . Lead wire, 3. . . 3. electrode for ion detection, . . Housing, 45. . . Cylinder head, 451. . . Swirl chamber,

Continued on the front page (51) Int.Cl. ⁶ Identification code FI F23N 5/12 F02P 17/00 E

Claims (9)

[Claims] 1. A glow plug comprising a housing and a main body supported in the housing, wherein the main body comprises:
A rod-shaped insulator, a current-carrying heating element printed and formed inside the rod-shaped insulator, and a pair of lead wires electrically connected to both ends of the current-carrying heating element and led out of the rod-shaped insulator; A glow plug, comprising an ion detection electrode for detecting a state of ionization in a flame, which is electrically insulated from a current-carrying heating element and disposed inside the rod-shaped insulator. 2. A glow plug comprising a housing and a main body supported in the housing, wherein the main body comprises:
A rod-shaped insulator consisting of an electrically insulating center shaft having a hollow portion and an insulating substrate coated on the outer periphery of the center shaft, and printed and formed between the center shaft and the insulating substrate inside the rod-shaped insulator; An electric heating element and a lead wire led out of the rod-shaped body from both ends of the electric heating element, and electrically insulated from the electric heating element, and inserted and fixed in the hollow portion of the center shaft for ionization in flame. A glow plug having an ion detection electrode for detecting a state. 3. The electric heating element according to claim 2,
A glow plug formed by printing on the inner surface of the insulating substrate. 4. The method according to claim 1, wherein:
A glow plug, wherein a tip of the ion detection electrode is exposed at a tip of the rod-shaped insulator so as to be exposed to the flame. 5. The method according to claim 1, wherein:
The ion detection electrode is made of MoSi ₂ , WC or TiN.
A glow plug characterized by being made of one or more kinds of conductive ceramic materials. 6. The method according to claim 1, wherein:
The ion detection electrode is one or two of W, Mo, and Ti.
A glow plug characterized by being made of at least one kind of high melting point metal. 7. The method according to claim 4, wherein
One or two of Pt, Ir, Rh, Ru, and Pd are provided on the exposed portion of the ion detection electrode exposed from the rod-shaped insulator.
A glow plug comprising at least one kind of noble metal. 8. The method according to claim 1, wherein:
The tip portion of the rod-shaped insulator has a hemispherical shape. 9. A method for manufacturing a glow plug according to claim 2, further comprising preparing a center shaft forming body made of an electrically insulating ceramic material and having a hollow portion, and inserting an ion detection electrode into the hollow portion. The energization heating element and the lead wire are printed on the surface of the formed body of the insulating substrate made of an electrically insulating ceramic material, and then the center formed body is placed on the printed surface of the insulating substrate. A glow plug is wound around the outer periphery of the center shaft, and then heated to fire the center shaft and the insulating substrate.