JPH1073070A - Ionic current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect an ionic current and thus accurately detect firing timing, a misfire and the like using the detected results. SOLUTION: A glow plug 1 includes a ceramic heating part 6 partly exposed inside a combustion chamber of a diesel engine. The ceramic heating part 6 comprises a heating element 7 which heats up upon the energization of its pair of lead wires, a heat-resistant insulator 8 in which the heating element 7 is embedded, and an ion-detection electrode 14 integrated with the heating element 7. A switch circuit 25 switches the glow plug 1 over between its heating- element heating state and its ionic-current detecting state. Under the ionic- current detecting state, an ECU 30 operates to detect a leakage current at a predetermined period before fuel firing. If a leakage current detected is larger than a preset threshold, the ECU 30 controls the switch circuit 25 to temporarily switch the glow plug 1 over from the ionic-current detecting state to the heating- element heating state. In this case, the temporary heating effect of the heating element 7 serves to remove carbon depositing on the outer periphery of the ceramic heating part 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an ion current detecting device for detecting an ion current generated during fuel combustion using a glow plug for promoting ignition and combustion of fuel.

[0002]

2. Description of the Related Art In recent years, not only gasoline engines but also diesel engines have been demanded to further reduce exhaust gas and exhaust gas exhausted from engines from the viewpoint of environmental protection. In order to respond to such demands, studies are being made on various engine improvements, reduction of exhaust gas by post-treatment (such as a catalyst), improvement of fuel and lubricating oil properties, and improvement of various engine combustion control systems.

In connection with the above considerations, recent engine combustion control systems are required to detect a combustion state during engine operation, and to detect in-cylinder pressure, combustion light, ion current, and the like. It has been studied to detect the combustion state of the engine. In particular, detecting the combustion state of an engine using an ion current is considered to be extremely useful because a chemical reaction accompanying the combustion can be directly observed, and various ion current detection devices have been proposed.

[0004] As an example of the ion current detecting device, a ceramic glow plug protruding into a combustion chamber to promote ignition and combustion of fuel is used. There is a technology provided with electrodes (for example, US Pat. No. 4,739,731).
issue). In such a glow plug, generally, a ceramic heating portion is composed of an insulator and a heating element embedded in the insulator,
An exposed electrode is provided on the outer periphery of the insulator. In this case, a predetermined voltage is applied between the exposed electrode and the inner wall (for example, a cylinder head) of the combustion chamber, and combustion ions generated during fuel combustion are captured by the electrode and the inner wall of the combustion chamber. And
The flow of the captured ions is detected as an ion current.

[0005]

However, the above-mentioned prior art has the following problems. That is, in the glow plug, carbon adheres to the outer periphery of the ceramic heat generating portion during its use, and the insulation resistance between the exposed electrode for detecting the ionic current and the earth portion (plug housing or cylinder head) insulated therefrom. Decrease. In this case, the electrode portion is electrically connected to the ground portion, which causes a situation in which a leakage current flows through the attached carbon although combustion ions are not originally generated. In such a situation, the ion current waveform is different from a desired waveform due to the leakage current, and the accuracy of the ignition timing detection process and the misfire detection process using the detection result deteriorates. The insulation state between the exposed electrode and the ground part depends on the pressure in the combustion chamber. In particular, during the compression stroke of the engine, the insulation resistance is reduced, and the leakage current easily flows.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to accurately detect an ion current and to use the detection result to detect ignition timing, misfire, and the like. An object of the present invention is to provide an ion current detection device capable of performing processing with high accuracy.

[0007]

According to the first aspect of the present invention, a heating state of a heating element by a glow plug and an ion current detection state by the glow plug are switched. means). Briefly describing the normal operation of this switching, for example, when the engine is started at a low temperature, the glow plug is kept in the heating element heating state, and then when the engine warm-up is completed by the heating action of the heating element, the glow plug is heated by the heating element. The state is switched from the state to the ion current detection state. That is, combustion ions are captured between the exposed electrode portion of the glow plug and the combustion chamber wall, and the ion current is detected by current detection means such as an ion current detection resistor.

In the present invention, a feature of the present invention is that a leak current flowing from an exposed electrode portion at a predetermined time before fuel ignition is detected in a state where an ion current is detected by a glow plug (leakage current detecting means). If the leakage current detected by the leakage current detection means is larger than a predetermined threshold, the switching means is operated to temporarily shift from the ion current detection state to the heating element heating state (operation means). .

In short, if carbon adheres to the outer peripheral portion of the glow plug in the combustion chamber, the insulation resistance between the exposed electrode and the ground decreases, and a leakage current flows. In this case, there arises a problem that a desired ion current waveform cannot be obtained.
That is, as shown in FIG. 6B, a leakage current flows prior to the original ion current waveform (before point A in FIG. 6). On the other hand, in the present invention, the leakage current is detected at a predetermined time (in FIG. 6, the timing of fuel injection), and the carbon adhesion state on the outer periphery of the glow plug can be estimated based on the leakage current. If the carbon is in such a state, the glow plug is set in a heating element heating state to burn off the deposited carbon. With the above configuration, a desired ion current waveform (for example, the waveform shown in FIG. 6A) can always be detected, and processes such as ignition timing detection and misfire detection using the detection result can be accurately performed. Can be.

When carbon adheres to the outer periphery of the glow plug, the insulation resistance between the exposed electrode and the earth side depends on the pressure in the combustion chamber. When the pressure rises, the insulation resistance decreases and leakage current easily flows. Therefore, in the invention described in claim 2, the leakage current is detected when the pressure in the combustion chamber rises. In this case, the presence or absence of the leakage current can be reliably detected. The time when the pressure rises corresponds to, for example, a compression stroke in a diesel engine.

According to the third aspect of the present invention, the leakage current is detected in accordance with the timing of fuel injection into the combustion chamber. That is, the timing of the fuel injection corresponds to, for example, a timing immediately before the combustion of the fuel when the pressure in the combustion chamber increases in a diesel engine. Therefore, under the condition that carbon is attached as described above, the leakage current can be detected more reliably.

On the other hand, in the invention described in claim 4, the operating means keeps the switching means in the heating element heating state for a time corresponding to the leakage current value detected by the leakage current detecting means. That is, the value of the leakage current increases as the amount of carbon attached to the outer periphery of the glow plug increases.
Therefore, if the retention time of the heating element heating state is determined according to the leakage current value, the deposited carbon can be reliably burned off.

According to a fifth aspect of the present invention, a high-pass filter is provided in a signal output section of an ion current detector for detecting an ion current. The signal is input to the signal processing device. According to the present invention, by using a high-pass filter as a component, even if carbon adheres to the ion detection electrode of the glow plug, an ion current generated during combustion and a leakage current due to insulation failure can be separated. As a result, the ion current can be reliably detected. In addition, if the combustion state information such as the ignition timing is determined based on the output waveform of the high-pass filter, the determination process is facilitated. It has been confirmed by the present inventors that the cut-off frequency of the high-pass filter may be set to about 50 Hz to 5 kHz, and more desirably to be set within the range of 100 to 500 Hz.

The invention described in claim 5 can be embodied as in claims 6 and 7 below. In other words, in the invention according to claim 6, the threshold value for the leakage current determination by the operation means is set near the allowable maximum value. In short, when the switching means is switched for the main purpose of removing adhering carbon, the threshold value for judging the leakage current may be set to a relatively low value. Even if the leakage current flows, the leakage current and the ionic current can be separated. Therefore, if the threshold value for determining leakage current is increased within an allowable range as described in claim 6, the ion current can be frequently detected instead of reducing the frequency of burn-off processing of the deposited carbon. Accordingly, the effect that the combustion state can be frequently detected is obtained.

According to a seventh aspect of the present invention, there is provided a comparing means for inputting an output signal of the high-pass filter and comparing the input signal with a threshold value for detecting a combustion state. In this case, by comparing the output of the high-pass filter with the combustion state detection threshold value, the combustion state detection process can be easily performed.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, a first embodiment of an ion current detecting device using a ceramic glow plug (hereinafter, simply referred to as a glow plug) will be described with reference to the drawings. That is, the ion current detection device of the present embodiment detects an ion current generated at the time of fuel combustion using a glow plug, and the glow plug includes a combustion chamber ( (A vortex chamber), a part of which is exposed to the combustion chamber. The glow plug plays a role of promoting the ignition and combustion of the fuel injected from the fuel injection nozzle when the engine is started at a low temperature. Also,
The glow plug according to the present embodiment has a role of detecting active ions present in the combustion flame zone during fuel combustion, in addition to the above-described start assist function.

FIG. 1 shows the entire structure of a glow plug 1 according to the present embodiment. In the figure, a glow plug 1 has a substantially cylindrical metal housing 2, and on the outer peripheral surface of the housing 2, a male screw portion 3 for attaching the glow plug 1 to a cylinder head described later and a hexagonal head 3 are provided. A part 4 is formed. Housing 2
A tubular protection tube 5 is welded to the upper part of the.

The housing 2 holds a cylindrical ceramic heat generating portion 6, which is composed of a conductive U-shaped heat generating member 7 and an insulating heat-resistant insulating material. Body 8, an ion detection electrode 14 integrally formed with the heating element 7, and two tungsten lead wires 9a and 9b connected to both ends of the heating element 7 and embedded in the insulator 8. It is configured.

More specifically, most of the heating element 7 is buried in the heat-resistant insulator 8 and is held firmly. As shown in the enlarged view of the main part of FIG. The end surface of the ion detection electrode 14 formed at the tip is provided on the same plane as the outer peripheral surface of the heat-resistant insulator 8. in this case,
Since the heating element 7 and the ion detection electrode 14 are integrally formed, the two members 7 and 14 are always in an electrically connected state. In such a configuration, the exposed portion of the heating element 7 and the inner wall of a vortex chamber 17 (broken line) of a diesel engine described later form a counter electrode for detecting an ion current. Note that, in the present embodiment, the ion detection electrode 14 corresponds to an exposed electrode portion.

In FIG. 1, conductive tips 10a and 10b embedded in a heat-resistant insulator 8 are connected to the upper ends of the tungsten lead wires 9a and 9b, respectively. Each has one lead wire
1a and 11b are connected. These two lead wires 11 a and 11 b are external signal input lines of the glow plug 1. The housing 2 and the protection tube 5 are electrically insulated from the lead wires 11a and 11b by an insulating tube 12 and a rubber bush 13. The lead wires 11 a and 11 b are fixed together with the rubber bush 13 by the swaging force of the protection tube 5.

Hereinafter, a detailed configuration of the ceramic heating section 6 will be described. That is, the heating element 7, the ion detection electrode 14, and the heat-resistant insulator 8 of the ceramic heating section 6 are all made of conductive ceramic powder (in the present embodiment, molybdenum silicide MoSi2 powder) and insulating ceramic powder (this embodiment). In this embodiment, the sintered body is made of a mixture of silicon nitride (Si3 N4 powder) and has a substantially equal blending ratio. However, in the heating element 7 and the ion detecting electrode 14, the average particle size of the MoSi2 powder is smaller than that of the Si3 N4 powder, and in the heat-resistant insulator 8, the average particle size of the MoSi2 powder is equal to or larger than that of the Si3 N4 powder. Has also been enlarged. That is, by changing the particle size of each powder, the heating element 7 and the electrode 14 for ion detection and the heat-resistant insulator 8 are separately formed.

In the ceramic heat generating portion 6 having the above-described structure, the heating element 7 and the ion detecting electrode 14 are composed of a small-diameter MoSi 2 powder (conductive ceramic powder) and a large-diameter Si
The 3N4 powder (insulating ceramic powder) surrounds and is connected to each other, so that a current flows through the heating element 7 and the electrode 14 for ion detection, and the heating element 7 generates heat. on the other hand,
In the heat-resistant insulator 8, since the small-diameter Si3N4 powder (insulating ceramic powder) is interposed between the large-diameter MoSi2 powder (conductive ceramic powder), the two are arranged in series and compared with the heating element 7. High resistance forms an insulating layer.

As a method of manufacturing the ceramic heating section 6, a mixture of MoSi2 powder and Si3N4 powder is first kneaded with a binder to form a paste, and the heating element 7, the ion detection electrode 14, and the heat-resistant insulator 8 are individually formed. And injection molding into a desired shape. Then, the heating element 7 and the electrode 14 for ion detection are arranged so as to be wrapped by the heat-resistant insulator 8, and 17.
After hot pressing at 00 to 1800 ° C., it is cut into a cylindrical shape as the ceramic heating part 6. Further, the heat-resistant insulator 8 is cut into a sphere at the tip of the ceramic heating section 6. As a result, the heating element 7 is entirely embedded with the heat-resistant insulator 8, but the end face of the ion detection electrode 14 is exposed at the tip of the ceramic heating section 6.

Next, an ion current detection system using the glow plug 1 configured as described above will be described with reference to FIGS. 3 and 4 are configuration diagrams each showing an outline of the ion current detection system according to the present embodiment. 3 shows a heating state of the glow plug 1 (heating element 7), that is, a state for promoting the ignition and combustion of the fuel at the time of starting the engine, and FIG. 4 shows an ion current accompanying the fuel combustion by the glow plug. 1 indicates a state to be detected.

In each figure, a screw hole 16 is formed in a cylinder head 15 of a diesel engine, and the glow plug 1 is screwed into the screw hole 16. That is, when screwing the glow plug 1 to the cylinder head 15, the hexagonal portion 4 is sandwiched by a predetermined tool, and the male screw portion 3 of the plug 1 is screwed into the screw hole 16.

The tip of the ceramic heat generating portion 6 of the glow plug 1 is arranged to protrude into a swirl chamber 17 formed in the cylinder head 15. The swirl chamber 17 has a piston 18
The main combustion chamber 19 provided at the upper part is communicated, and the swirl chamber 17 forms a part of the combustion chamber. The tip of a fuel injection nozzle 20 is disposed in the swirl chamber 17, and fuel is injected from the fuel injection nozzle 20 into the swirl chamber 17.

A switching circuit 25 as switching means is provided between the glow plug 1 and the battery 21 composed of a DC power supply having a rated voltage of 12 V (volt). The electric path between the battery 21 and the glow plug 1 is switched according to the operation state of the position changeover switches 23 and 24. The switch circuit 25 normally holds the ion current detection state (the state shown in FIG. 4) when a command signal from an electronic control unit (hereinafter referred to as ECU) 30 is not input. The state shifts from the ion current detection state to the heating element heating state (the state in FIG. 3). At this time, the two changeover switches 23 and 24 operate simultaneously.

That is, the terminals 2 of the changeover switches 23 and 24
3a and 24a are the lead wires 11 of the glow plug 1.
a and 11b (and tungsten lead wires 9a and 9b) are connected to each other. The changeover switch 23,
Reference numeral 24 denotes two contacts 23b, 23c, and 24 each selectively connected to the terminals 23a and 24a.
b, 24c.

In such a case, in the heating element heating state, as shown in FIG. 3, the path between the terminal 23a and the contact 23b is closed, and the path between the terminal 24a and the contact 24b is closed. At this time, the positive side of the battery 21 is connected to one lead wire 11a of the glow plug 1 via a terminal 23a and a contact 23b, and the other lead wire 11b is connected to the battery 21 via a terminal 24a and a contact 24b. The negative side is connected. That is, the heating element 7 is maintained in a heated state (at this time, current flows through a path shown by a two-dot chain line in FIG. 3). The contact 24b is
It is also connected to a part of the cylinder head 15 as a ground part.

In the ion current detection state, as shown in FIG. 4, the path between the terminal 23a and the contact 23c is closed, and the path between the terminal 24a and the contact 24c is closed.
That is, the changeover switches 23 and 24 are both open. In this case, the battery voltage is applied to the lead wire 11a via the ion current detecting resistor 26 on the electric path (path indicated by the two-dot chain line in FIG. 4) provided in parallel with the changeover switch 23. That is, a battery voltage is applied between the ion detection electrode 14 formed at the tip of the ceramic heat generating portion 6 and the cylinder head 15, and the generation of active ions in the combustion flame zone is indicated by a two-dot chain line in FIG. Ion current flows through the path.

The resistance value of the ion current detecting resistor 26 is about 100 kΩ, and the ion current flowing through the ion current detecting resistor 26 is detected by a potentiometer 27 as a potential difference between both ends of the resistor 26.

Here, the principle of detecting the ion current will be briefly described. When the fuel injected by the fuel injection nozzle 20 is used for combustion in the swirl chamber 17, a large amount of ionized positive ions and negative ions are generated in the combustion flame zone. At this time, when a battery voltage is applied between the ion detection electrode 14 and the cylinder head 15 (the inner wall of the vortex chamber 17) facing the ion detection electrode 14, the ion detection electrode 14 captures negative ions, Cylinder head 15
Captures positive ions. As a result, the current path shown in FIG. 4 is formed, and the ion current flowing through this current path is detected as a potential difference between both ends of the ion current detection resistor 26.

On the other hand, the ECU 30 has a CPU, ROM, R
A well-known microcomputer including an AM and an input / output circuit and an A / D converter (both not shown) are mainly configured to input a detection signal detected by the potentiometer 27.
In addition, a detection signal of a water temperature sensor 31 for detecting the temperature of the engine cooling water and a detection signal of a rotation speed sensor 32 for detecting the engine rotation speed according to the engine crank angle are input to the ECU 30. Detects the water temperature Tw and the engine speed Ne based on the detection signals of the sensors 31 and 32.

When the diesel engine is started at a low temperature, the ECU 30 heats the heating element 7 of the glow plug 1 to promote ignition and combustion of the fuel. When the warm-up of the diesel engine is completed, a switching command signal is output to the switch circuit 25, and the circuit of the present system is set to the ion current detection state to detect the combustion ion current.
At the beginning of the engine start, the switch circuit 25
Are maintained in a heating element heating state by the ECU 30. Hereinafter, the switching process of the switch circuit 25 will be described with reference to the flowchart of FIG. FIG.
Is executed by interruption processing for a predetermined time.

Now, when the processing of FIG. 5 starts, EC
U30 first determines whether or not the engine has been warmed up in step 110 and the switch circuit 25 is in the ion current detection state. At the beginning of the engine start, a negative determination is made in step 110, and the ECU 30 reads the water temperature Tw and the engine speed Ne in the subsequent step 120.

Thereafter, the ECU 30 determines in step 130 that the water temperature Tw is equal to the predetermined warm-up completion temperature (in this embodiment, 6
0 ° C.) or more, and
At 40, it is determined whether or not the engine speed Ne has reached a predetermined speed (2000 rpm in the present embodiment) or more. In such a case, if both steps 130 and 140 are negatively determined, the ECU 30 determines that the warm-up of the engine has not been completed and that heating by the glow plug 1 (the heating element 7) is necessary, and proceeds to step 150. . If any of steps 130 and 140 is affirmatively determined, E
The CU 30 determines that the warm-up of the engine has been completed or that heating by the glow plug 1 (the heating element 7) is unnecessary, and proceeds to step 160.

When the process proceeds to step 150, the ECU 30
Indicates that the switch circuit 25 is in the heating element heating state (the state of FIG. 3).
, And then the process ends. In this state, the ignition and combustion of the fuel are promoted by the heat generation effect of the glow plug 1.

When the process proceeds to step 160, EC
U30 shifts the switch circuit 25 from the heating element heating state to the ion current detection state (the state of FIG. 4), and thereafter ends this routine. In this state, the ion current generated during fuel combustion is detected by the ion current detection resistor 26.

The case where the determination in step 140 is affirmative and the process proceeds to step 160 may be, for example, a case where the engine speed Ne temporarily increases in the racing state. In this case, the engine warm-up is not yet completed. I haven't. Therefore, even if the switch circuit 25 once shifts to the ion current detection state, the ECU 30 makes a negative determination in step 110 in the next processing and performs the determination processing in steps 130 and 140 again. When the temporary increase in the engine speed Ne stops and the engine speed Ne decreases (Ne <2000 rpm), the switch circuit 25 is reactivated.
Return to the heating element heating state (step 150).

Thereafter, when Tw ≧ 60 ° C. and the engine warm-up is completed, the ECU 30 makes an affirmative decision in step 110. After the engine warm-up is completed and the switch circuit 25 shifts to the ion current detection state, the ECU
30 is affirmatively determined at step 110 each time, and step 17 is performed.
Go to 0.

The ECU 30 reads the current value Ip detected by the ion current detection resistor 26 at the fuel injection timing in step 170, and then reads the current value Ip in step 180.
Is greater than or equal to a predetermined threshold value Ith.
This current value Ip corresponds to a value of a leakage current flowing due to carbon attached to the outer periphery of the ceramic heat generating portion 6. If a negative determination is made in step 180 (if Ip <Ith), the ECU 30 terminates this routine. In such a case, it is determined that the carbon is not attached to the outer periphery of the ceramic heat generating portion 6 or the attached carbon is equal to or less than the allowable amount, and the switch circuit 25 is maintained in the ion current detection state.

On the other hand, if the determination in step 180 is affirmative (if Ip ≧ Ith), the ECU 30 proceeds to step 190
Then, the switch circuit 25 is moved from the ion current detection state (the state of FIG. 4) to the heating element heating state (the state of FIG. 3).
Move to That is, if the determination in step 180 is affirmative, it is considered that carbon exceeding the allowable amount has adhered to the outer periphery of the ceramic heat generating portion 6. Therefore, the insulation resistance between the ion detection electrode 14 and the earth side (the housing 2 and the cylinder head 15 side) decreases due to the attached carbon, and a leakage current flows (Ip ≧ Ith).

Thereafter, in step 200, the ECU 30 holds the heating element heating state for a predetermined time (2 seconds in the present embodiment). Further, the ECU 30 sets the switch circuit 25 in the ion current detection state (FIG.
After this, the present routine is terminated. In the present embodiment, step 170 in FIG. 5 corresponds to the leakage current detecting means described in the claims, and steps 180 and 1
90 corresponds to the operation means described in the claims.

FIG. 6 is a current waveform diagram when an ion current generated during fuel combustion is observed using an oscilloscope. However, FIG. 6A shows a state where carbon is not attached to the outer periphery of the ceramic heat generating portion 6, and FIG. 6B shows a state where carbon is attached to the outer periphery of the ceramic heat generating portion 6.

In FIG. 6A, the waveform in which the voltage sharply rises immediately after the fuel injection timing is the ion current waveform due to fuel combustion, and point A corresponds to the combustion start position, that is, the ignition timing. At this time, the current value is held at substantially 0 at the timing of the fuel injection. In addition, two peaks are observed in the ion current waveform. That is, in the early stage of combustion, the first peak B1 is generated by the active ions of the diffusion flame zone.
Is observed, and in the latter half of the combustion, the second peak B2 is observed by re-ionization due to an increase in the in-cylinder pressure.

In this case, the ECU 30 detects the actual ignition timing from the first peak B1 of the ion current waveform,
Feedback control of the ignition timing is performed to eliminate the difference between the detected actual ignition timing and the target ignition timing. Further, the ECU 30 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 fuel injection control. By reflecting the ion current in the fuel injection control of the engine in this manner, it is possible to control the operating state of the engine finely.

On the other hand, in FIG. 6B, a leakage current exceeding an allowable level (threshold value Ith) is observed at the timing of fuel injection. Therefore, in this state, the attached carbon is removed by the heating action of the heating element 7. In the state where the carbon is attached, if the state is left as it is, the leakage current value gradually increases, and it may be difficult to distinguish the first peak from the first peak, but such an inconvenience is also avoided. You.

Next, effects of the present embodiment will be described. (A) As described in detail above, in the present embodiment, under the ion current detection state by the glow plug 1, the current value Ip as the leakage current is detected at the timing of the fuel injection, and the current value Ip becomes a predetermined value. The switch circuit 25 is operated to temporarily shift from the ion current detection state to the heating element heating state if the threshold value Ith or more is reached. That is, based on the current value Ip as the leakage current, the state of carbon deposition on the outer periphery of the ceramic heat generating portion 6 is estimated. Was burned off. As a result, a desired ion current waveform can be always detected, and processes such as ignition timing detection and misfire detection using the detection result can be accurately performed.

(B) In this embodiment, the leakage current (current value Ip) is detected at the timing of fuel injection. That is, the timing of the fuel injection corresponds to the timing when the pressure in the combustion chamber of the diesel engine increases and immediately before the combustion of the fuel. Therefore, under the condition that carbon is attached as described above, the leakage current can be detected reliably.

(C) As described above, in the present embodiment, since the adhering carbon is removed each time, the durability of the glow plug 1 having the ion current detecting function can be improved.

(D) Further, in the configuration of the ion current detection device of the present embodiment, the switching circuit 25 switches between the heating element heating state and the ion current detection state, and the power supply used in both states is shared. (Battery 2
1). Therefore, the configuration relating to ion current detection can be simplified, and an inexpensive ion current detection device can be provided.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
The embodiment will be described with reference to FIGS. 7 and 8. FIG.
However, in the configuration of the following embodiment, the first
The description of what is equivalent to the embodiment is simplified. The following description focuses on differences from the first embodiment.

FIG. 7 shows an outline of an ion current detection system according to the second embodiment. In FIG. 7, an HPF (high-pass filter) 4 is provided at the signal output section of the potentiometer 27.
1 is connected. In this embodiment, about 200 Hz
The HPF 41 is configured to pass a frequency signal exceeding the frequency range. The output of the HPF 41 is connected to a non-inverting input terminal of a comparator 42 constituting a comparing unit. The comparator 42 compares a threshold voltage Vth input to its inverting input terminal with the output of the HPF 41, and outputs a binary signal of a logic high level or a logic low level according to the magnitude comparison between the two. Is output to the ECU 30.

The ion current detection system having the above configuration operates as follows. The control operation of the ECU 30 is basically the same as that of FIG. 5 in the first embodiment,
In the present embodiment, in order to reduce the frequency of setting the switch circuit 25 to the heating element heating state in order to remove the adhered carbon, the threshold value Ith to be compared with the ion current value Ip is set in the first embodiment. Is larger than the set value. That is, in the first embodiment, since the main purpose is to remove the adhered carbon, the threshold value I for comparing and determining the leakage current (ion current value Ip) is set.
While th (see step 180 in FIG. 5) is set to a relatively low value, in the present embodiment, the detected ion current is around the allowable maximum value within the range where the combustion state can be determined. Is set as a threshold value (It in FIG. 8).
h1> Ith in FIG. 6 (b).

In step 180 of FIG. 5 executed by the ECU 30, the ion current value Ip at the fuel injection timing is compared with the threshold value Ith1, and the switch circuit 25 is temporarily turned on only when Ip ≧ Ith1 is satisfied. The state is shifted from the ion current detection state to the heating element heating state.

Therefore, as shown in FIG. 8, even if a small amount of leakage current flows, the ion current value Ip at that time falls below the threshold value Ith1, and the ion current detection state is maintained. Then, in this state, the HPF4
1 is input to the comparator 42 and is compared with a predetermined threshold voltage Vth. In this case, the timing at which the output of the HPF 41 rises (the timing of P in FIG. 8) corresponds to the ignition timing of the fuel. Therefore, the output of the comparator 42 (the signal which rises to a logic high level) corresponds to the ignition timing of the fuel. Become. Then, the ECU 30 determines the fuel ignition timing from the output of the comparator 42. Incidentally, if there is a misfire state, the output of the comparator 42 does not rise to a logical high level, and the ECU 30 determines occurrence of misfire from that fact.

According to the present embodiment, the effects described in the first embodiment can be obtained, of course.
The following effects are also obtained. (A) In the present embodiment, the HPF 41 is provided at the output of the potentiometer 27 corresponding to the signal output unit of the ion current detector,
The detection signal is input to the ECU 30. According to this configuration, by incorporating the HPF 41 into the circuit, even if carbon adheres to the ion detection electrode 14 of the glow plug 1, an ion current generated during combustion and a leakage current due to insulation failure can be separated. The ion current can be reliably detected. Further, by determining the combustion state information such as the ignition timing based on the output waveform of the HPF 41, the determination process is facilitated.

(B) Threshold value I for determining leakage current
th1 (see FIG. 8) was set near the allowable maximum value. In short, in the configuration of the present embodiment, even if a small amount of leakage current flows, the leakage current and the ionic current can be separated. Therefore, if the threshold value Ith1 for determining the leakage current is increased within the allowable range, the ion current can be frequently detected instead of the frequency of the burn-off processing of the adhering carbon, and accordingly, the combustion state frequently increases. The effect of being able to detect is obtained.

(C) The output of the HPF 41 is input to a comparator 42, which compares the signal input from the HPF 41 with a threshold voltage Vth for detecting a combustion state, and outputs the comparison result to the ECU 30. I did it. In this case, the detection process of the combustion state can be easily performed.

The embodiment of the present invention can be realized in the following modes other than the above. (1) In the above embodiments, the leakage current (current value Ip) is detected at the timing of fuel injection (step 170 in FIG. 5), but this may be changed. For example, the leakage current may be detected at a predetermined crank angle before TDC. The predetermined crank angle is given as a pulse output timing of a predetermined number obtained from a detection signal of the rotation speed sensor 32. In short, when carbon adheres to the outer periphery of the glow plug, the insulation resistance between the exposed electrode and the earth side depends on the pressure in the combustion chamber. Therefore, the detection time of the leakage current may be any time before the fuel is ignited and in the state where the in-cylinder pressure is high, that is, during the compression stroke. However, when a large amount of carbon adheres to the outer periphery of the glow plug, a leakage current is observed at any timing. Therefore, it is desirable to detect the leakage current in the compression stroke as described above. It is not something to be done.

(2) In each of the above embodiments, FIG.
In step 200, the switch circuit 25 is held in the heating element heating state for a predetermined time (two seconds) set in advance. However, the holding time may be variably set. For example, as shown in FIG.
The time (holding time) for maintaining the heating element heating state is set according to the current value Ip read at 0. According to FIG.
The holding time is set to be longer as the current value Ip (leakage current) becomes larger. In this case, the attached carbon can be more reliably removed. Note that the characteristic shown in FIG. 9 can be given by a non-linear function.

(3) The shape of the glow plug may be changed as follows. That is, the heating element 7 and the electrode 1 for ion detection
4 may be separately provided, and these may be electrically connected. In short, any structure may be used as long as an exposed electrode portion exposed on a part of the heat-resistant insulator 8 is provided.

In each of the above embodiments, an all-ceramic glow plug is used, but another glow plug may be used. For example, a coil-shaped metal wire (for example, a tungsten wire) as a heating element is embedded in a heat-resistant insulator made of a ceramic material, and a part of the metal wire has an ion detection electrode (exposed electrode) exposed to a combustion flame. Section) is electrically connected. Also in this case, an inexpensive glow plug having an ion current detecting function can be provided. In addition, the heat generation performance of the heating element can be maintained for a long time.

(4) In each of the above-described embodiments, two switching modes are used to switch between the heating element heating state and the ion current detection state.
Switch circuit 25 including position changeover switches 23 and 24
Was used, but this may be changed. For example, the switch may be changed to a semiconductor switch (transistor, thyristor, or the like) capable of controlling a large current. In short, any means capable of switching between the above two states may be used.

(5) In each of the above embodiments, a common DC power supply (vehicle-mounted battery 21) is used in the heating element heating state and the ion current detection state. However, a configuration using two DC power supplies may be used. Specifically, a heating element heating power supply for heating the heating element 7 and an ion current detection power supply for detecting an ion current are prepared. For example, a rated 12 V (volt) power supply is used as the heating element heating power supply. Uses a DC power supply (vehicle-mounted battery), rated 5 as a power supply for ion current detection
A DC power supply of 0 V (volt) is used.

(6) In each of the above embodiments, the present invention is applied to the ion current detecting device for detecting combustion ions of a diesel engine having a swirl chamber. However, a so-called direct injection type fuel is directly injected into the combustion chamber. The present invention may be applied to an engine. Further, the present invention can be applied to other devices. For example, in a device that burns unburned fuel in the exhaust pipe of a gasoline engine, it is possible to detect combustion ions accompanying the combustion of the unburned fuel by the ion current detection device of the present invention. In this case, the combustion state of the unburned fuel can be determined from the ionic current detected by the device.

(7) In the second embodiment, the HPF
Although the output of 41 is input to the comparator 42, this may be changed. For example, the output of HPF41 is directly EC
The information may be input to U30, and the ignition timing may be determined and the presence or absence of misfire may be processed in the ECU 30. In this case, the ECU 30 corresponds to the comparing means described in the claims.

(8) In the second embodiment, the HPF
Although the cutoff frequency of 41 is 200 Hz, this may be changed. In short, the HPF must be within a range where the ion current generated during combustion and the leakage current due to insulation failure can be separated.
May be set. According to the experiment of the present inventor, it has been confirmed that the above-mentioned effect is obtained when the frequency is in the range of 50 Hz to 5 kHz, and more desirably, the frequency is set in the range of 100 to 500 Hz. Also, H
For example, the PF may be changed to a differentiating circuit including a CR circuit.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing an outline of a glow plug according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a main part of the glow plug.

FIG. 3 is a schematic view of the ion current detection system, showing a heating element in a heated state.

FIG. 4 is a schematic diagram illustrating an outline of an ion current detection system and illustrating an ion current detection state.

FIG. 5 is a flowchart showing a procedure for switching a switch circuit.

FIG. 6 is a diagram showing an example of an ion current waveform.

FIG. 7 is a configuration diagram illustrating an outline of an ion current detection system according to a second embodiment.

FIG. 8 is a time chart illustrating an ion current processing operation in the second embodiment.

FIG. 9 is a diagram for setting a time period for temporarily holding a switch circuit in a heating element heating state under an ion current detection state in another embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glow plug, 7 ... Heating element, 14 ... Electrode for electrode detection as an exposed electrode part, 17 ... Swirl chamber which forms a combustion chamber, 2
DESCRIPTION OF SYMBOLS 1 ... Battery (power supply), 25 ... Switch circuit as a switching means, 26 ... Ion current detection resistance which comprises an ion current detector, 27 ... Potentiometer which comprises an ion current detector, 30 ... Leakage current detection means Operation means, ECU (electronic control device) constituting a signal processing device, 41 ... H
PF (high pass filter), 42... A comparator as comparing means.

Claims (7)

[Claims] A glow plug having a heating element for generating heat by power supply from a power supply and having an exposed electrode part partially insulated from the other is used for fuel combustion in a combustion chamber using the glow plug. An ion current detection device that detects an generated ion current, comprising: a switching unit that switches between a heating state of a heating element by the glow plug and an ion current detection state by the glow plug; and an ion current detection state by the glow plug. A leak current detecting means for detecting a leak current flowing from the exposed electrode portion at a predetermined time before fuel ignition, and temporarily if the leak current detected by the leak current detecting means is larger than a predetermined threshold value Operating means for operating the switching means to shift from the ion current detection state to the heating element heating state. Ion current detection device according to symptoms. 2. The ion current detection device according to claim 1, wherein said leakage current detection means detects a leakage current when the pressure in the combustion chamber rises. 3. The ion current detecting device according to claim 1, wherein said leakage current detecting means detects a leakage current in accordance with a timing of fuel injection into a combustion chamber. 4. The operating means holds the switching means in the heating element heating state for a time corresponding to a leakage current value detected by the leakage current detecting means.
The ion current detection device according to any one of the above. 5. The ion according to claim 1, wherein a high-pass filter is provided in a signal output section of the ion current detector for detecting the ion current, and the detection signal is input to a signal processing device. Current detector. 6. The ion current detecting apparatus according to claim 5, wherein a threshold value for determining a leakage current by said operating means is set near an allowable maximum value. 7. The ion current detection device according to claim 5, further comprising comparison means for inputting an output signal of the high-pass filter and comparing the input signal with a combustion state detection threshold value.