JPH109113A - Ion current detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect an ion current with a high percision even in the glow period established by the glow plug, and further, maintain combustion of the fuel in a good condition by the use of the detection result of the ion current. SOLUTION: A ceramic heating part 6 of a glow plug 1 includes a heating element 7 which is electrified to be heated by a pair to leads, a heat-resisting insulator 8 which buries the heating element 7 and an ion detecting electrode 14 which is integrally formed on the heating element 7. A first and second transistors Tr1 and Tr2 perform ON/OFF operation receiving a command signal from the ECU 30, and change the heated condition of the heating element heated by the glow plug and the ion current detection condition. Then, under the heated condition of the heating element, the ECU 30 operates the transistors Tr1 and Tr2 (turns OFF them) so as to temporarily become an ion current detection condition immediately after the ignition of fuel to detect an ion current in the temporary OFF period of the transistors Tr1 and Tr2.

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 and detection methods 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 in which a part is provided (for example, US Pat. No. 4,739,731).
issue). In such a glow plug, a predetermined voltage is applied between the electrode portion 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 portion and the inner wall of the combustion chamber. Then, the flow of the captured ions is detected as an ion current.

[0005] In an ion current detecting device using a glow plug having such an ion current detecting function, ignition and combustion of fuel are generally promoted by the heat-generating action of the heating element at the beginning of the low-temperature start of the engine. In this case, usually, the warming-up of the engine is completed, and the heating state of the heating element is continued until the combustion state is stabilized (generally called an afterglow). Then, after the end of the afterglow, the heat generation function of the glow plug is stopped, and the ion current detection process is started.

[0006]

However, the above-mentioned prior art has the following problems. That is, the existing ion current detection device only exhibits a heating effect during the after-glow period as described above, and cannot detect the ion current. Therefore, during such a period, the combustion state control using the detection result of the ion current cannot be performed, and there has been a problem that the combustion state cannot be optimally controlled. Specifically, during the afterglow period, for example, it is not possible to perform the ignition timing feedback control and the misfire detection process using the detection result of the ion current, and it is difficult to control the combustion state of the fuel to an optimum state. there were.

The present invention has been made in view of the above circumstances, and has as its object to accurately detect an ionic current even during a glow period by a glow plug, and to thereby obtain a result of detecting the ionic current. It is an object of the present invention to provide an ion current detection device which can maintain a good combustion state of a fuel by using the same.

[0008]

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). At this time, in the ion current detection state by the glow plug, combustion ions are captured between the 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, as a feature, the switching means is operated so as to temporarily enter the ion current detection state at least immediately after the ignition timing of the fuel under the heating state of the heating element by the glow plug (operation means). .
That is, for example, during the after-glow period when the engine is started at a low temperature, the role of promoting the ignition and combustion of the fuel is given the highest priority as the function of the glow plug. Therefore, in the conventional device, the ion current detection process is performed during the after-glow period. I wasn't. On the other hand, according to the present invention, even under a heating state of the heating element such as the after-glow period, the ion current detection period is provided temporarily within a range that does not impair the heat generation function of the glow plug. Therefore, the ion current can be accurately detected even during the glow period by the glow plug, and the fuel combustion state can be maintained in a good state by using the detection result of the ion current.

[0010] In the invention described in claim 2, the operating means operates the switching means such that the ion current is detected for a predetermined period from the timing of fuel injection into the combustion chamber. In this case, by setting the ion current detection period based on the fuel injection timing, the ion current detection period is set as short as possible to reliably detect the ion current and minimize the deterioration of the glow function due to the glow plug. Can be minimized.

According to the third aspect of the present invention, the operating means switches the heating element heating state and the ion current detection state at a predetermined frequency. Even in such a case, both the ion current detection function and the heating element heating function can be achieved during the afterglow period.

According to the fourth aspect of the present invention, the glow plug is formed integrally with the heating element which is electrically heated by a pair of lead wires, a heat-resistant insulator for burying the heating element, and the heating element. The glow plug detects ion current generated during fuel combustion. In this case, although the configuration is very simple, the ion current can be accurately detected, and the information can be effectively used for combustion control.

[0013]

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 ceramic heat generating portion 6, which is
A U-shaped heating element 7 having conductivity, a heat-resistant insulator 8 having insulating properties, an ion detection electrode 14 integrally formed with the heating element 7, and connected to both ends of the heating element 7. And two tungsten leads 9a and 9b embedded in the insulator 8.

More specifically, the heating element 7 is largely buried in the heat-resistant insulator 8 and 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.

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 heating section 6 having the above-described structure, the heating element 7 and the ion detecting electrode 14 are formed by converting a small-diameter MoSi2 powder (conductive ceramic powder) to 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 portion 6, first, a mixture of MoSi2 powder and Si3N4 powder is 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 each 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 the configuration diagram of FIG. 3, a screw hole 16 is formed in a cylinder head 15 of the 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 plug 1
The male screw part 3 of the above is screwed into the screw hole 16.

The tip of the ceramic heat generating portion 6 of the glow plug 1 is disposed so as 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.

Further, the present ion current detection system includes a battery 21 composed of a DC power supply having a rated voltage of 12 V (volt).
The collector of the first transistor Tr1 is connected. The emitter of the first transistor Tr1 is connected to one lead wire 11a of the glow plug 1, and the base is connected to an electronic control unit (hereinafter referred to as ECU) 30. The negative side of the battery 21 is connected to the emitter of the second transistor Tr2. Further, the collector of the second transistor Tr2 is connected to the other lead 11b of the glow plug 1, and the base is E
It is connected to CU30. In the above configuration,
The base of the second transistors Tr1 and Tr2 has an ECU
The same command signal from 30 is input, and these transistors Tr1 and Tr2 always operate in synchronization. In addition,
The emitter of the second transistor Tr2 is also connected to a part of the cylinder head 15. In the present embodiment,
The first and second transistors Tr1 and Tr2 correspond to a switching means.

In this case, when an H-level command signal is input from the ECU 30 to the bases of the first and second transistors Tr1 and Tr2, the transistors Tr1 and Tr2 are turned off.
Tr2 is turned ON, and lead wires 11a, 11b and tungsten lead wire 9a,
The battery voltage will be applied via 9b. That is, when the transistors Tr1 and Tr2 are driven ON, the heating element 7 is maintained in a heated state (this state is referred to as a heating element heated state).

The first and second transistors Tr1, Tr1
When the command signal to Tr2 goes low, the transistors Tr1 and Tr2 are both turned off, and the battery voltage is applied to the lead wire 11a via an electric path provided in parallel with the first transistor Tr1. That is,
A battery voltage is applied between the ion detection electrode 14 formed at the tip of the ceramic heating section 6 and the cylinder head 15. In this case, an ion current flows along with the generation of active ions in the combustion flame zone, and this ion current is detected by the ion current detection resistor 26 (this state is referred to as an ion current detection state).

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. Then, the ion current flowing in such a state is detected as the 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.

The ECU 30 heats the heating element 7 of the glow plug 1 by turning on the first and second transistors Tr1 and Tr2 mainly at the time of starting the diesel engine at a low temperature, thereby igniting and burning the fuel. Promote (afterglow operation). When the warm-up of the diesel engine is completed, the transistor Tr
1, Tr2 is turned off, and the circuit of the present system is set to the ion current detection state, and the combustion ion current is detected.

Particularly, in this embodiment,
The first and second transistors Tr1 and Tr2 are temporarily turned off during a predetermined period after fuel ignition so that the ion current can be detected from the beginning of the engine start (during the afterglow period).
FF is performed to temporarily shift from the heating element heating state to the ion current detection state.

Hereinafter, the operation of the present embodiment will be described with reference to FIGS. First, using the time chart of FIG.
An outline of the operation in the present embodiment will be described. FIG. 4
Shows the ion current waveform generated at the time of fuel combustion, the fuel injection timing, and the ON / OFF operation state of the transistors Tr1 and Tr2 when the engine is started at a low temperature.
Before the time t1 in the figure, an afterglow period is shown, and this time t1 corresponds to the end time of the afterglow.

During the afterglow period (before time t1), the heating element heating state is mainly continued,
An ion current detection period is temporarily provided therein. That is, in the after-glow period, the transistors Tr1 and Tr2 are turned on as an initial state, and thereby the heating element 7 is in a heated state. Further, in order to obtain the ion current waveform as shown in the figure, the transistors Tr1 and Tr2 are temporarily turned off for a predetermined period (90 ° CA in the present embodiment) from the fuel injection timing. Then, during this temporary ion current detection period (Tr1, Tr2
The detection result of the ion current during the OFF period is employed for controlling the combustion state.

In the ion current waveform of FIG. 3, the waveform in which the voltage (the voltage detected by the potentiometer 27) sharply rises immediately after the fuel injection timing (immediately after the compression TDC) is the ion current waveform due to fuel combustion. Corresponds to the combustion start position, that is, the fuel ignition timing. Further, two peaks B1 and B2 are observed in this ion current waveform. That is, in the early stage of combustion, the first peak B1 is observed by active ions in the diffusion flame zone, and in the second half of combustion, the second peak B2 (peak value) is observed by re-ionization due to an increase in in-cylinder pressure.

In FIG. 4, 90 ° from the fuel injection timing
The CA ion current detection period and the heating element heating period up to the next fuel injection timing (approximately 630 ° CA) are repeated (however, only one cylinder is shown in the present embodiment). Since the ion current detection period is temporary, the function of igniting and burning fuel by the glow plug 1 is not impaired.

At time t1, the first and second transistors Tr1 and Tr2 are both turned off, and the heating operation of the heating element 7 is stopped in accordance with the operation of the transistors Tr1 and Tr2 (afterglow is terminated). Is done).
At this time, the circuit of the present system enters the ionic current detection state, and thereafter, the ionic current is detected every fuel combustion.

Next, the arithmetic processing performed by the ECU 30 to realize the above-mentioned afterglow operation and ion current detection operation will be described with reference to the flowcharts of FIGS. Note that FIG.
FIG. 6 shows an on / off switching routine of r1 and Tr2, and FIG. 6 shows a fuel ignition timing feedback control routine as an example of combustion state control using the detection result of the ion current.

First, FIG. 5 will be described. Note that FIG.
Is executed by interruption processing for a predetermined time. By the way, when the processing of FIG.
First, at step 110, it is determined whether or not the present time is during the afterglow period. For this determination, for example, a flag set during the afterglow period (when the engine is cold) may be used. At the beginning of the low temperature start of the engine, the affirmative determination is made in step 110, and the ECU 30 determines in step 120 that the water temperature Tw and the engine speed Ne
Read.

Thereafter, the ECU 30 determines in step 130 whether or not the water temperature Tw is equal to or higher than a predetermined after-glow end temperature, that is, a warm-up completion temperature (60 ° C. in the present embodiment). Engine speed N
e is a predetermined number of revolutions (2000 rpm in the present embodiment)
It is determined whether or not the above has been reached. In such a case, if both steps 130 and 140 are negatively determined, the ECU 30
Indicates that the engine has not been warmed up and glow plug 1
It is determined that heating by the (heating element 7) is necessary, and the process proceeds to step 150. If any of steps 130 and 140 is affirmatively determined, the ECU 30 determines that the warm-up of the engine has been completed or that the heating by the glow plug 1 (heating element 7) has become unnecessary, and proceeds to step 160.

When the process proceeds to step 150, the ECU 30
Are, as described above, the first and second transistors Tr1, T
r2 is turned on, the circuit in FIG. 3 is set to the heating element heating state, and under the heating element heating state, the transistors Tr1 and Tr2 are temporarily turned off to put the circuit in FIG. 4). In particular,
From the timing of fuel injection, the first and
The second transistors Tr1 and Tr2 are turned off. Then, after the processing of step 150, the present routine ends. In this state, the ignition and combustion of the fuel are promoted by the heat generation action of the glow plug 1, and the ionic current accompanying the combustion of the fuel can be detected. In the present embodiment, the processing of step 150 corresponds to an operation means described in the claims.

When the process proceeds to step 160, EC
U30 turns off the first and second transistors Tr1 and Tr2, thereby shifting the circuit of FIG. 3 to the ion current detection state. In this state, the ion current is continuously detected. Then, after the processing of step 160, the present routine ends.

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 is temporarily increased in the racing state. In this case, the engine warm-up is not yet completed. I haven't. Therefore, even if the circuit of FIG. 3 has once shifted to the ion current detection state, the ECU 30 determines that the afterglow is still continuing and makes an affirmative determination in step 110 in the next processing, and performs the determination processing in steps 130 and 140. Perform again. Then, when the temporary increase in the engine speed Ne stops, and the engine speed Ne decreases (Ne <2000).
rpm), the processing of step 150 is performed again.

Thereafter, when Tw ≧ 60 ° C. and the engine warm-up is completed, that is, when the after-glow period ends,
Thereafter, the ECU 30 makes a negative determination every step 110. That is, the first and second transistors Tr1, Tr
2 is maintained in the OFF state, and the circuit of FIG. 3 is maintained in the ion current detection state.

Next, the fuel ignition timing feedback control will be described with reference to FIG. The flow shown in the figure is executed by the ECU 30 every time fuel is injected into a cylinder. In addition,
The ignition timing control of the fuel is realized by adjusting the fuel injection timing. In the present embodiment, the ignition timing of the fuel is optimized by adjusting the fuel injection timing by the fuel injection nozzle to the optimal timing. Feedback control is to be performed.

In FIG. 6, the ECU 30 first uses the fuel ignition timing map stored in the memory in advance at step 210, and determines the optimal fuel ignition timing (optimal ignition timing) according to the engine speed Ne and the fuel injection amount Q at that time. Time K
Find a). Here, the fuel injection amount Q is obtained from the engine load (for example, accelerator depression amount) at that time and the engine speed.

In step 220, the ECU 30 determines the actual fuel ignition timing (actual ignition timing Kb) based on the ion current waveform (the first peak B1 in FIG. 4). Is calculated using the following equation (1).

KAVi = {KAVi−1 · (n−1) + Kbi} / n (1) In the present embodiment, the smoothing coefficient n is “8”. Thereafter, the ECU 30 determines in step 240 that the deviation Δ between the optimal ignition timing Ka and the smoothed value KAV of the actual ignition timing Kb.
In addition to calculating K (= Ka−KAV), in a subsequent step 250, a well-known feedback method (for example, a PI method or a PID method) is used to correct the optimal ignition timing Ka calculated in the step 210 according to the deviation ΔK. . Then, the fuel injection timing is actually controlled based on the optimum ignition timing corrected and calculated in this manner.

By reflecting the ion current in the fuel injection control of the engine as described above, it becomes possible to control the operating state of the engine finely. In the above description, an example of the feedback control of the ignition timing using the detection result of the ion current has been described. However, other combustion state control such as performing misfire detection using the detection result of the ion current may be performed. (Not shown). For example, a combustion state such as abnormal combustion or misfire may be detected from the second peak B2 of the ion current waveform in FIG. 4, and the detection result may be reflected in fuel injection control.

Next, effects of the present embodiment will be described. (A) As described in detail above, in the present embodiment, the transistors Tr1 and Tr2 are temporarily set to the ion current detection state immediately after the fuel injection timing under the heating state of the heating element by the glow plug (after glow period). Operated. According to such a configuration, it is possible to detect the ion current within a range that does not impair the heat generation function of the glow plug 1 under the heating element heating state. As a result, the ion current can be accurately detected even during the glow period by the glow plug 1, and the combustion state of the fuel can be maintained in a good state by using the detection result of the ion current.

(B) In particular, in this embodiment, since the ion current detection period is set based on the fuel injection timing, the ion current detection period is set as short as possible to reliably detect the ion current. A decrease in the glow function due to the glow plug 1 can be minimized.

(C) In this embodiment, the first and second transistors Tr1 and Tr are used as switching means.
2 was adopted. Therefore, a switching operation with good responsiveness can be performed.

(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.

(E) In addition, in this embodiment, the ion detecting electrode 14 is formed integrally with the heating element 7 of the glow plug 1, and the ion detecting electrode 14 and the engine cylinder head 15 are formed. The ion current generated during fuel combustion is detected by the electrode. In this case, although the configuration is very simple, the ion current can be accurately detected, and the information can be effectively used for combustion control.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
The embodiment will be described with reference to FIG. However, in the configuration of the present embodiment, the same components as those of the above-described first embodiment are denoted by the same reference numerals in the drawings, and the description is simplified. The following description focuses on differences from the first embodiment.

This embodiment is characterized in that the transistors Tr1 and Tr2 are turned on / off by an on / off signal of a predetermined frequency during the afterglow period. FIG. 7 is a time chart showing a specific operation of the present embodiment. The time t11 in FIG.
Previously, an afterglow period was shown, and this time t11 corresponds to the end time of the afterglow.

In the after-glow period (before time t11), the first and second transistors Tr1, T
r2 is continuously switched between the ON state and the OFF state. In such a case, O of the transistors Tr1 and Tr2
The N period corresponds to the heating element heating period, and the transistor Tr
The OFF period of 1, Tr2 corresponds to the ion current detection period. At this time, the detection result of the ion current in the ion current detection period (the OFF period of Tr1 and Tr2) is employed for controlling the combustion state.

Here, the first and second transistors Tr
For example, the frequency at which Tr1 is switched is preferably 10 kHz or more when the ignition timing is detected using the detection result of the ion current. In this case, if the frequency is lower than this, the accuracy of detecting the ignition timing may be deteriorated in a high engine speed range. Further, in the case where misfire or abnormal combustion is detected using the detection result of the ion current, it is desirable that the switching frequency be 1 kHz or more. In this case, if the frequency is lower than this, the accuracy of detecting misfire or abnormal combustion may deteriorate in a high engine speed range. In this embodiment, the frequency is set to 10 kHz.
z.

In the same figure, immediately after the fuel injection timing (immediately after the compression TDC), an ion current waveform due to fuel combustion is observed at a predetermined cycle. In this case, the ignition timing, misfire, abnormal combustion, and the like of the fuel can be detected by analyzing the individual detection levels.

As described above, according to the second embodiment, similarly to the first embodiment, the ionic current can be accurately detected even during the glow period by the glow plug 1, and the detection result of the ionic current can be obtained. The fuel combustion state can be maintained in a good state by using.

The present invention can be realized by the following embodiments in addition to the above embodiments. (1) In the first embodiment, step 15 in FIG.
0, a predetermined period (90 ° CA
Although the first and second transistors Tr1 and Tr2 are turned off and switched to the ionic current detection state only during the period), the ionic current detection period may be variably set. For example, an ion current detection period under a heating element heating state (afterglow period) is set according to the engine load and the engine speed. In this case, the larger the engine load or the higher the engine speed, the longer the ion current detection period. On the other hand, the smaller the engine load or the lower the engine speed, the shorter the ion current detection period. preferable.

(2) In each of the above embodiments, the temporary ion current detection period is provided in the afterglow period at the time of starting the engine at a low temperature. It is also possible to provide an effective ion current detection period. For example, when carbon adheres to the outer periphery of the glow plug,
Even when the attached carbon is burned off by the heat generating action of the heating element, a temporary detection state of the ion current is set under the heating state of the heating element. In such a case, the combustion state control can be continued without interruption.

(3) In each of the above embodiments, the procedure for detecting the ion current for a single-cylinder engine (or one cylinder of a multi-cylinder engine) has been described. An ion current detection procedure may be applied.

(4) In each of the above embodiments, an all-ceramic type glow plug is used, but other glow plugs 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.

(5) In the above embodiments, the first and second transistors Tr1 and Tr2 are used as semiconductor switches for switching between the heating element heating state and the ion current detection state.
Was used, but this may be changed. For example, it may be changed to another semiconductor switch such as a thyristor, or may be changed to a contact switch. In short, any means capable of switching between the above two states may be used.

(6) In the above embodiment, 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 50 V as a power supply for ion current detection
(Volt) DC power supply.

(7) 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, but a so-called direct injection type in which 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.

[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 configuration diagram showing an outline of an ion current detection system.

FIG. 4 is a time chart for explaining the operation in the first embodiment more specifically;

FIG. 5 is a flowchart showing a procedure for switching ON / OFF of a transistor.

FIG. 6 is a flowchart showing a fuel ignition timing feedback procedure.

FIG. 7 is a time chart for more specifically explaining the operation in the second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glow plug, 7 ... Heating element, 8 ... Heat resistant insulator, 9
a, 9b: tungsten lead wire, 11a, 11b: lead wire, 14: electrode for ion detection, 17: vortex chamber forming a combustion chamber, 21: battery (power supply), 30: ECU (electronic control device) as operating means , Tr1... A first transistor as switching means, Tr2... A second transistor as switching means.

Claims (4)

[Claims] 1. An ion current detecting device, wherein a heating element that generates heat by power supply from a power supply has a glow plug protruding into a combustion chamber, and detects an ion current generated during fuel combustion using the glow plug. Switching means for switching between a heating state of the heating element by the glow plug and an ion current detection state by the glow plug;
Operating means for operating the switching means so as to temporarily enter the ion current detection state at least immediately after the ignition timing of the fuel. 2. The ion current detecting device according to claim 1, wherein said operating means operates the switching means so as to be in an ion current detecting state only for a predetermined period from the timing of fuel injection into the combustion chamber. 3. The ion current detection device according to claim 1, wherein said operation means switches the heating element heating state and the ion current detection state at a predetermined frequency. 4. The glow plug includes a heating element which is electrically heated by a pair of lead wires, a heat-resistant insulator having the heating element embedded therein, and an ion detection electrode formed integrally with the heating element. The ion current detection device according to any one of claims 1 to 3, further comprising: detecting an ion current generated during fuel combustion using the glow plug.