JPH1089222A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug to dissolve a problem on adhesion of carbon, detect an ion current with high precision, and be excellent in durability. SOLUTION: A glow plug comprises an energization heat generating body 2 in a U-shape in cross section arranged at the internal part of an insulating body 11; and an electrode 3 for detecting ion electrically connected to the middle of the energizing heat generating body 2 and disposed at the internal part of the insulation body. The tip thereof is exposed in a manner to be exposed to flame. Provided electrical resistance of a first heat generating part ranging from a plus end 218 being on the plus side of the energization heat generating body 2 to a first connection part 39 of the electrode 3 for detecting ion is R1, electrical resistance of a second heat generating part ranging from the first connection part 39 to a minus end 228 is R2, and electrical resistance ranging from the first connection part 39 of the electrode 3 for detecting ion to a tip is (r), a relation of R2>r is satisfied.

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.

The present invention has been made in view of the above problems, and aims to provide a glow plug which can solve the problem of carbon adhesion, can accurately detect ion current, and has excellent durability. is there.

[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 U-shaped cross section provided inside the insulator. And a pair of lead wires electrically connected to both ends of the energizing heating element and led out of the insulator, and the insulating member electrically connected in the middle of the energizing heating element. And one or a plurality of ion detection electrodes for detecting the state of ionization in the flame, which is disposed inside the flame, and the tip of the ion detection electrode is exposed to the flame. Exposed from the insulator,
In addition, when a direct current for heating is supplied to the current-carrying heating element, a current is supplied from the positive end of the current-carrying heating element, which is on the plus side, to the center of the first connection portion to which the first ion detection electrode is connected. The electric resistance of the first heat generating part of the heat generating element is R1, and the second heat generating part of the current generating heat element from the center of the first connection portion between the current generating element and the ion detection electrode to the minus end of the current generating element. The electric resistance of R2
The glow plug is characterized in that the relationship of R2> r is satisfied, where r is the electric resistance from the first connection portion to the tip of the ion detection electrode.

What is most notable in the present invention is that an energizing heating element and an ion detection electrode are disposed inside the insulator, and the electric resistance R2 of the second heating section of the energizing heating element is: That is, it is larger than the electric resistance r of the first connection portion.

In the present invention, the current-carrying heating element has a first heating portion extending from the plus end to the center of a first connection portion with the first ion detection electrode, and a minus portion from the center of the first connection portion. The end is constituted by the second heat generating portion. The electric resistance of the first heat generating portion is R1,
The electric resistance of the heating section is R2 (FIG. 4).

The first connection portion is a portion of the current-carrying heating element to which an ion detection electrode is first connected in a path from a plus end to a minus end. This is because the ion detection electrode is one (FIG. 4) or plural (FIG. 10)
This is because there is a case where is provided. Therefore, when a plurality of ion detection electrodes are provided, a portion between the plus end and the nearest ion detection electrode located closest to the plus end becomes the first heat generating portion, and the vicinity ion detection electrode and the minus end are connected to each other. The second heat generating portion is between the two (FIG. 10). Therefore, one or a plurality of ion detection electrodes may be connected to the second heat generating portion.

Next, when the electric resistance R2 of the second heat generating portion of the energizing heating element and the electric resistance of the ion detecting electrode are set to satisfy R2> r as described above, both materials and
Alternatively, it is achieved by changing the thickness, thickness, length, etc. of the current supply path. For example, as a means for changing the material, the mixing ratio between the conductive ceramic powder and the insulating ceramic material is different between the second heat generating portion and the ion detection electrode.

As the raw materials for the energizing heating element and the ion detecting electrode, for example, MoSi ₂ , Mo ₅ Si ₃ , Mo _X S
i ₃ C _Y ( _X = 4 to 5, _Y = 0 to 1), MoB, WC,
At least one kind of conductive ceramic such as a metal silicide, carbide, nitride, boride such as TiN is used. As insulating ceramics, Si ₃ N ₄ , Al ₂ O ₃ , B
N or the like is used. At least one oxide of a rare earth element is added as a sintering aid.

Hereinafter, MoSi is used as a conductive ceramic.
₂ is described using Si ₃ N ₄ as an insulating ceramic and Y ₂ O ₃ and Al ₂ O ₃ as sintering aids. That is, the particle size of Si ₃ N ₄ is M
By making the particle size larger than the particle size of oSi ₂ , the insulating Si ₃ N ₄ particles become conductive MoSi ₂ particles which are continuous with each other.
It becomes a tissue wrapped in particles and expresses conductivity.

Specifically, MoSi ₂ having an average particle size of 1 μm
And Si ₃ N ₄ having an average particle size of 15 μm. Similarly, the sintering aid also had an average particle size of 1 μm. MoSi ₂ and Si ₃ N ₄
Is appropriately selected in the range of 10 to 60: 90 to 40 (% by weight). The second heating part of the current-carrying heating element is MoS
If i ₂ , Si ₃ N ₄ = 20: 80 and the electrode for ion detection is MoSi ₂ : Si ₃ N ₄ = 40: 60, R
2> r. The sintering aids are Y ₂ O ₃ and Al ₂ O
A total of 10 wt% of ₃ was externally added. As sintering aids, oxides of rare earth elements other than Y ₂ O ₃ , Yb ₂ O ₃ ,
_{La 2 O 3, Nd 2 O} 3 may be like, using one or more selected from these.

Here, the conductor is a mixture of a conductive ceramic and an insulating ceramic, but may be a conductive ceramic alone. Further, a mixture of metal powder and insulating ceramic may be used by using metal powder instead of the conductive ceramic in the mixture. Alternatively, only metal powder or metal wire may be used.

Next, the insulators are, for example, MoSi ₂ which is a conductive ceramic and Si ₃ N which is an insulating ceramic.
₄ as a basic component, and Y ₂ O ₃ , Al ₂ O
_It consists of a ceramic sintered body to which ₃ is added. And Si
₃ The particle size of N _4, by the same or slightly smaller and MoSi _2, conductive MoSi ₂ particles of the insulating Si ₃ N
It becomes a divided tissue surrounded by _four particles, and expresses insulation. Specifically, for example, Mo having an average particle size of 0.9 μm
Si ₂ and Si ₃ N ₄ having an average particle diameter of 0.6 μm can be used.

It is more preferable that the energizing heating element, the ion detection electrode, and the insulator have the same or nearly the same compounding ratio because the difference in the coefficient of thermal expansion and the like becomes small. As the sintering aid, an oxide of a rare earth element other than Y ₂ O ₃ , for example, an oxide of ytterbium, lanthanum, neodymium, or the like may be used, and one or more selected from these are used.

The electric resistance R2 of the second heat generating portion is 0.1 to 5Ω, and the electric resistance r of the electrode for ion detection is 0.0.
It is preferable to set the resistance to 5 to 2.5 Ω from the viewpoint of the glow plug heater characteristics.

In arranging the electric heating element and the electrode for ion detection in the insulator, for example, as shown in FIG. And molded into one piece. Connect the lead wires at the same time as molding. For the lead wire, a high melting point metal such as tungsten or molybdenum or an alloy thereof is used.

Alternatively, an integrally formed product comprising the above-mentioned electric heating element and the electrode for ion detection is sandwiched between two separately formed insulator molded bodies. Such an insulator molded product or an integrally molded product of an electric heating element and an electrode for ion detection is prepared by, for example, premixing a ceramic powder and a resin material as a binder, and injecting the mixed material. It is produced by the following. Then, it is fired.

Further, the electric heating element and the ion detecting electrode may be provided by printing inside the insulator. An example of such printing is as follows. For example, an electric heating element made of a conductive material 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. The lead wire and the electrode for ion detection are printed.
Next, the formed form is wound and then fired. As a result, an insulator containing the printed heating element, lead wire, and ion detection electrode is obtained.

The firing of the injection molded product or the printed product is performed by
Sinter by hot pressing. The conditions are, for example,
1 atm, pressurized 400 kg / c under argon gas atmosphere
m ² , a sintering temperature of 1800 ° C. and a holding time of 60 minutes.

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, the electric resistance R2 of the second heat generating portion is formed to be larger than the electric resistance r of the ion detecting electrode. Therefore, when carbon adheres to the surface of the insulator in the glow plug and the carbon electrically short-circuits between the electrode for ion detection and the cylinder head as described above (see FIG. 4), By applying a direct current to the carbon, the carbon between the ion detection electrode and the cylinder head can be reliably burned off.

That is, in the present invention, when the above-mentioned direct current is applied at the time of burning off the above-mentioned carbon, the electric resistance R2 of the above-mentioned second heat generating portion of the electric heating element and the electric resistance r of the electrode for ion detection become R2> r. Therefore, the direct current flows from the plus end to the cylinder head via the first heat generating portion, the ion detection electrode, and the attached carbon. Therefore, the carbon on the surface of the insulator generates heat, and the heat and the air in the combustion chamber burn and burn off the carbon. Therefore, a short circuit due to the adhesion of carbon can be easily eliminated. Therefore, the ion current can be accurately detected over a long time.

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. Can be demonstrated. 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.

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 provided inside the insulator. Therefore,
ADVANTAGE OF THE INVENTION According to this invention, the problem of carbon adhesion can be solved, the ion current can be detected accurately, and the glow plug excellent in durability can be provided.

Next, as in the second aspect of the present invention, it is preferable that the electric resistance R2 of the second heat generating portion be at least twice as large as the electric resistance r of the ion detecting electrode. In this case, the carbon can be more reliably burned off.

Next, according to a third aspect of the present invention, the ion detecting electrode is made of a conductive ceramic material containing at least one of a metal silicide, carbide, nitride, and boride. Alternatively, it can be made of a mixed material of the conductive ceramic material and the insulating 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, according to a fourth aspect of the present invention, the ion detecting electrode is made of one or two or more refractory metal materials whose main components are metals having a melting point of 1200 ° C. or more, or the refractory metal material. And an insulating ceramic material. In the case of the former metal, since the raw material can be used in a linear form, the effect of reducing the cost of the material, processing and assembly can be obtained.

In the latter case, the high temperature strength and the oxidation resistance are improved, and the coefficient of linear expansion between the heating element and the insulator can be easily adjusted and combined. can get. The reason for setting the melting point to 1200 ° C. is that the current-carrying heating element of the glow plug is 1000 to 1100 ° C.
This is because the heat resistance of the ion detection electrode was considered in order to generate heat.

Next, as in the fifth aspect of the present invention, the exposed portion of the ion detecting electrode
Preferably, one or more noble metals of t, Ir, Rh, Ru, and Pd are provided. In this case, the effect of improving the wear resistance and oxidation resistance of the detection electrode can be obtained.

[0036]

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, the housing 4 includes a housing 4 and a main body 10 supported in the housing 4.

The main body 10 includes an insulator 11, an electric heating element 2 having a U-shaped cross section provided inside the insulator 11, and electrically connected to both ends of the electric heating element 2. Has a pair of lead wires 21 and 22 led out.
In addition, it has one ion detection electrode 3 that is electrically connected in the middle of the current-carrying heating element 2 and disposed inside the insulator 11 for detecting the state of ionization in the flame. . The tip of the ion detection electrode 3 is exposed from the insulator 11 so as to be exposed to the flame.

Then, as shown in FIG. 4, the first connection in which the first ion detecting electrode 3 is connected from the plus end 218 on the plus side when a direct current for heating is supplied to the energizing heating element 2. Up to the center 209 of the part 39,
The electric resistance of the first heating portion 201 in the energizing heating element 2 is represented by R
1, the second heating portion 2 of the current-carrying heating element 2 from the center 209 of the first connection portion 39 to the minus end 228
The relationship of R2> r is satisfied, where R2 is the electrical resistance of 02, and r is the electrical resistance from the first connection portion 39 to the tip 30 of the ion detection electrode 3.

As shown in FIGS. 1 and 2, the main body 10 is provided inside 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 rises inside the insulator 11 and is electrically connected to a terminal portion 31 provided at the upper end.

The ion detecting electrode 3 is provided integrally with the energizing heating element 2 at the lower end of the U-shaped energizing heating element 2, and the tip 30 is exposed from the insulator 11. The tip 30 is coded with platinum (Pt).

On the other hand, the housing 4 is
1 and, as shown in FIG. 1 and FIG. Further, the housing 4 has a male screw portion 43 for mounting to the cylinder head 45 of the engine. As shown in FIG. 2, a rubber bush 421 is fitted into the upper opening of the protective cylinder 42. Also,
The external lead wire 233 inserted through the rubber bush 421,
333 is connected to the internal lead wires 231 and 33 via connection terminals 232 and 332, respectively.

Therefore, the external lead wires 233, 333
Are electrically connected to the electric heating element 2 and the ion detection electrode 3 respectively. The tip (lower end) of the main body 10 is formed in a hemispherical shape as shown in FIGS.

Next, in manufacturing the glow plug main body 10, first, as shown in FIG. 3, an integrally molded product 29 of the heating element 2 and the electrode 3 for ion detection is prepared. The integrally molded article 29 includes an electric heating element 2 and an ion detecting electrode 3.
Is mixed with a mixed binder of paraffin wax and a resin as main components, and the mixture is injection-molded. Alternatively, the ceramic powder is press-formed as it is.

The integrally molded article 29 is made of the insulator 1
1 and are baked under pressure by a hot press. The above pressure firing is performed in an argon gas atmosphere at 1 atm, a pressure of 400 kgf / cm ² , a firing temperature of 1800 ° C., and a holding time of 60 minutes. Prior to the embedding, the lead wires 21 and 22 are connected. Thereby, the glow plug main body 10 is obtained.

Next, specific examples of the ceramic powder and the like are as follows.
As described above, MoSi ₂ is used as the conductive ceramic of the heating element, the ion detection electrode, and the insulator, and Si ₃ N ₄ is used as the insulating ceramic. Further, Y ₂ O ₃ and Al ₂ O ₃ are used as sintering aids.

The mixing ratio of ceramic in the electric heating element was set to MoSi ₂ : Si ₃ N ₄ = 20: 80. The mixing ratio of the electrode for ion detection is MoSi ₂ : Si
₃ N ₄ = 40: 60. The average particle size of MoSi ₂ was 1 μm, and the average particle size of Si ₃ N ₄ was 15 μm. The mixing ratio of the ceramic in the insulation _{MoSi 2: Si 3 N 4 =} 30: 70 and, MoSi ₂
And the average particle size of Si ₃ N ₄ was 1 μm. The sintering aid is Y ₂ O in any of the above cases.
₃ wt% and Al ₂ O ₃ 5 wt% were externally added. The average particle size of each material was 1 μm.

Next, as shown in FIG. 5, the glow plug 1 composed of 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 one external lead wire 333. Further, the external lead wire 333 is connected to the other end of the electric heating element 2 via the internal lead wire 33 and the lead wire 22 (FIG. 1) in the main body 10. 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 ECU 52 is connected to the glow relays 53 and 531 ion relay 530, a water temperature sensor 525 for the engine cooling water, and an engine speed sensor 526 for the engine.

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 energized heating element 2 of the glow plug is closed, and the first heating section 201 and the second heating section 202 of the energized heating element 2 of the glow plug body 10 are energized to generate 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, 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.

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 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 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 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. This flow is executed by interruption processing for a predetermined time. First, when the process of FIG. 6 starts, the ECU 52 first determines in step 11 whether or not the engine has been warmed up and the glow relays 53 and 531 are 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 an affirmative determination is made in any of steps 13 and 14, it is considered that the warm-up of the engine has been completed or that heating by the glow plug 1 is not necessary.
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. 7A is a current waveform diagram when observing an ion current generated during fuel combustion 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
7B, when carbon (soot) generated by fuel combustion adheres, that is, when smoke is generated, as shown in FIG. 7 (B), the ion current is low before the fuel injection timing and rises thereafter. The phenomenon of going out occurs (compare (A) and (B) of FIG. 7). It should be noted that Ith in FIG. 7B represents a peak value determination level (threshold 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 relay 53 is turned on, the heating element 2 is heated, and the operation of burning off the attached carbon is performed.

FIG. 8 is a flow chart in which this carbon burn-off 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 of FIG. 7, it is determined in step 22 whether the abnormal ion current (FIG. 7B) as described above is detected at the fuel injection timing. If not, the process proceeds to step 25, and the glow relay 53 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 energize the energizing heating element 2 of the glow plug.

What is important here is that, as shown in FIG. 4, the electric resistance R
2 is larger than the electrical resistance r of the ion detection electrode 3.
Therefore, the direct current for heating entered from the positive end of the current-carrying heating element 2 is supplied from the first heating section 201 to the ion detection electrode 3.
And then flows to the cylinder head 45 via the carbon 49 attached to the surface of the insulator 11.

At this time, the carbon 49 generates heat by the direct current, and is oxidized and burned off by the air in the swirl chamber and burned off. Therefore, the glow plug returns to the normal state again. Therefore, the glow relays 53 and 531 are turned off and the ion relay 530 is turned on again to detect the ion current.

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, a direct current is applied to the carbon 49 as described above to heat the carbon 49, thereby burning off the carbon, and heating the carbon 49. Can be brought into a 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, the turbulence of the combustion flame flow in the combustion chamber is suppressed, the detection performance is stabilized, and the concentration of thermal stress is suppressed to absorb the thermal shock. it can.

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. The ion detection electrode 3 is disposed at the center of the insulator 11 in the diameter direction. Therefore, ion currents in all directions in the combustion chamber can be detected with high accuracy.

Embodiment 2 As shown in Table 1, this embodiment shows a specific example of the glow plug body 10 shown in Embodiment 1 in which the ratio between the electric resistances R2 and r is changed. In manufacturing the glow plug main body 10, first, the above-mentioned integrally formed article 29 (FIG. 3) is prepared in advance by injection molding of the heating element 2 and the electrode 3 for ion detection.

On the other hand, the insulator 11 is prepared as a semi-cylindrical two-piece product. The semi-cylindrical body is provided with a U-shaped groove for embedding the integrally molded article 29 in a portion (diameter portion) that is on the inside when the insulator 11 is formed (see FIG. 1).
Then, the integrally molded article 29 is put into the U-shaped groove of the semi-cylindrical body of the insulator 11, further covers one of the semi-cylindrical bodies, and is sintered under pressure. As a result, as shown in FIG. 1, an insulator 11 having the electric heating element 2 and the ion detection electrode 3 built therein, which is an integrally molded product, is obtained.

Next, the current-carrying heating element 2 is combined with 35% (weight ratio, hereinafter the same) of MoSi ₂ powder, which is a conductive ceramic powder, so that the electric resistance R2 of the second heating section is 0.8Ω. And a mixture of 65% of Si ₃ N ₄ powder as an insulating ceramic material. Further, the ion detecting electrode 3 is set so as to have an electric resistance r shown in Table 1 below.
The ratio between the MoSi ₂ powder and the Si ₃ N ₄ powder was changed.

The insulator 11 is made of Si ₃ N ₄ powder and M
Using a mixture of the OSI ₂ powder. The ratio is
The Si ₃ N ₄ powder was 80% and the MoSi ₂ powder was 20%.
In addition, the sintering aid is 5% by weight of Y ₂ O _{3 and} 5% by weight of Al ₂ O ₃ for the heating element, the electrode for ion detection and the insulator.
Was added externally. The average particle size of each material was the same as that of the first embodiment. And the above pressure sintering is 400 kg / c
m ² , 1800 ° C., 60 minutes.

Next, the various glow plugs constructed as described above are connected to the cylinder head 45 as in the first embodiment.
Attached to. Then, as shown in FIG. 4, the surface of the insulator 11 was made to have carbon adhered thereto, and the quality of burnt-out (burned out) of the adhered carbon was tested. The results are shown in Table 1.

[0076]

[Table 1]

As can be seen from Table 1, when R2> r (Nos. 1 to 4), carbon is burned off.
In particular, in the case of R2 ≧ 2r (Experiment Nos. 1 to 3), it can be seen that excellent burn-off can be performed. In the case of R2 ≦ r (Experiment Nos. 5 and 6), almost no DC current flows through the carbon, so that the carbon does not burn out.

Third Embodiment In the second embodiment, the case where MoSi ₂ is used as the conductive ceramic of the current-carrying heating element and the ion detecting electrode has been described. However, as the conductive ceramic, carbide of another metal, Similar results can be obtained by using nitrides and borides. In this example, to confirm this, Table 2,
As shown in Table 3, the conductive ceramics were WC, Mo ₂ C,
_{TiN, Mo 4.8 Si 3 C 0.6} , WSi 2, MoB, T
iB ₃ and ZrB ₂ , and the resistance value of each was changed to No. 2 of the second embodiment. 3, No. Samples similar to level 6 were prepared, and carbon burnout experiments were performed on these samples. The average particle size of each material is 1-3 μm. Others are the same as the second embodiment.

Further, different materials were used for the conductive heating element and the conductive ceramic of the ion detecting electrode. Further, the same operation was performed in the case where the insulating ceramic was changed from Si ₃ N ₄ to Al ₂ O ₃ or BN. The average particle diameter of Al ₂ O ₃ was 25 μm, and the average particle diameter of BN was 10 μm. Others are the same as the second embodiment. The results of the experiment are shown in Tables 2 and 3.

Table 4 also shows the case where only the conductive ceramic is used for both the current-carrying heating element and the ion detecting electrode. As is clear from Tables 2 to 4, it can be seen that carbon is completely burned off within the scope of the present invention.

[0081]

[Table 2]

[0082]

[Table 3]

[0083]

[Table 4]

Embodiment 4 Next, a case where a high melting point metal wire is used for an ion detection electrode and a case where a mixture of a high melting point metal material and an insulating ceramic is used for an ion detection electrode will be described. First,
The case where a refractory metal wire is used as the ion detection electrode will be described. Here, the high melting point metal has a melting point of 12 as described above.
It refers to one with a temperature of 00 ° C or higher. As such a high melting point metal,
Cr, Co, Fe, Mo, Ni, Re, Ti, W, Zr
Etc. In addition, Fe-Ni-Cr, Ni-Co, Fe
There are also alloy materials such as -Co and W-Re.

The composition of the second embodiment was used for the current-carrying heating element. Further, the structure of the ion detecting electrode was the same as the structure of the ion detecting electrode 3 shown in FIG. In each case, no. 3, No. Create the same resistance value as the level of 6,
A carbon burnout experiment was performed. Others are the same as the second embodiment. Table 5 shows the results. It can be seen from the table that carbon is burned off within the scope of the present invention.

Next, a mixture of a high melting point metal material and an insulating ceramic was used for the ion detection electrode. In manufacturing the glow plug, the above metal powder was used instead of MoSi ₂ which was the conductor of the ion detection electrode of the second embodiment. The average particle size of each material was 1 to 10 μm. Others are the same as the second embodiment. Table 6 shows the results. It can be seen from the table that carbon is burned off within the scope of the present invention.

[0087]

[Table 5]

[0088]

[Table 6]

Fifth Embodiment As shown in FIG. 9, this embodiment is a modification of the glow plug operating circuit (FIG. 5) of the first embodiment. The battery 54 and the DC power supply 51 of the first embodiment are different from each other. One battery 5
Only 5 is replaced. The glow relay 53 is provided between the positive side of the battery 55 and the external lead 233, and the glow relay 53 operates between the external lead 333 and the negative side of the battery 55 in the same manner as the glow relay 53. Glow relay 531 is provided.

Further, an ion relay 530 is provided between the external lead wire 233 and the ion current detecting resistor 521 as in the first embodiment. When the energized heating element is heated, the glow relays 53 and 531 are turned on, and the ion relay 530 is turned off. When detecting the ion current, reverse the above.

A constant current / constant voltage circuit 524 can be interposed between the ion current detecting 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 6 As shown in FIG. 10, this embodiment is an example in which two ion detection electrodes 301 and 302 are provided on both left and right sides of a U-shaped current-carrying heating element 2. In this example, since the ion detection electrode 301 is located at a position near the positive end of the current-carrying heating element 2, this portion becomes the first connection portion 39 between the current-carrying heating element 2 and the ion detection electrode 3. Therefore, a portion from the first connection portion 39 to the ion detection electrode 301 to the minus end becomes the second heat generating portion 202.

At the time of carbon burning, a direct current for burning flows from the ion detecting electrode 301 to the carbon on the surface of the insulator 11. Further, in this example, since two ion detection electrodes are provided, the ion current can be detected with higher accuracy. Other configurations are the same as those of the first embodiment, and the same effects as those of the first embodiment can be 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 a perspective view of an integrally formed product of an electric heating element and an electrode for ion detection according to the first embodiment.

FIG. 4 is an explanatory diagram of an operation and effect in the first embodiment.

FIG. 5 is a glow plug operation circuit diagram according to the first embodiment.

FIG. 6 is a flowchart of the glow plug operation system according to the first embodiment when the glow plug is started.

FIGS. 7A and 7B 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. 8 is a flowchart of smoldering determination in the first embodiment.

FIG. 9 is a glow plug operation circuit diagram according to a fifth embodiment.

FIG. 10 is an overall explanatory diagram of a glow plug according to a sixth embodiment.

[Explanation of symbols]

 1. . . Glow plug, 10. . . Body, 11. . . Insulator, 2. . . Energizing heating element, 201. . . First heat generating section, 202. . . Second heat generating part, 21, 22,. . . Lead wire, 3. . . Electrode for ion detection, 39. . . 3. first connection, . . Housing, 45. . . Cylinder head, 451. . . Vortex chamber, 49. . . carbon,

Claims (5)

[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 having a U-shaped cross section 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; One or a plurality of ion detection electrodes for detecting a state of ionization in a flame, which is electrically connected to the middle of the current-carrying heating element and disposed inside the insulator; The tip of the electrode for ion detection is exposed from the insulator so as to be exposed to the flame, and the plus end of the current-generating heating element which is on the positive side when a direct current for heating is supplied to the current-generating element. , The electric resistance of the first heat generating portion in the current-carrying heating element from the center to the center of the first connection portion to which the first ion-detecting electrode is connected is R1, the first resistance of the current-carrying heating element and the ion detection electrode is From the center of the connection Assuming that the electric resistance of the second heat generating portion of the current-carrying heating element up to the terminal end is R2 and the electric resistance from the first connection portion to the tip of the ion detection electrode is r, the relationship of R2> r is satisfied. A glow plug characterized by the fact that: 2. The glow plug according to claim 1, wherein the magnitude of the electric resistance is R2 ≧ 2r. 3. The ion detecting electrode according to claim 1, wherein the main component of the ion detecting electrode is a metal silicide, carbide, nitride, or the like.
A glow plug made of one or more boride conductive ceramic materials, or a mixed material of the conductive ceramic material and an insulating ceramic material. 4. The method according to claim 1, wherein:
The electrode for ion detection is made of one or two or more high-melting metal materials whose main components are metals having a melting point of 1200 ° C. or more, or a main material composed of a mixture of the high-melting metal material and an insulating ceramic material. A glow plug characterized by the following. 5. The method according to claim 1, wherein:
A glow plug, wherein one or more noble metals of Pt, Ir, Rh, Ru, and Pd are provided on an exposed portion of the ion detection electrode exposed from the insulator.