JPH11273828A - Ignition plug and ignition and ion current detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect ions as an ion current by efficiently gathering the ions generated in a combustion compartment during combustion at a center electrode of an ignition plug. SOLUTION: A conductor part 28 of U-shape is adhered to a center electrode 23 of an ignition plug 21 by welding or the like, and the conductor part 28 is protruded below a grounding electrode 27 in a combustion compartment 29. After spark discharge has been generated between the center electrode 23 and the grounding electrode 27 when igniting, electric field directed from the conductor part 28 towards an inner wall of the combustion compartment 29 is formed in the combustion compartment 29 by applying a positive voltage to the center electrode 23, and thereby a negative ion generated during combustion is gathered by the conductor part 28 (center electrode 23), for detecting an ion current. Since the conductor part 28 is protruded below the grounding electrode 27, the electric field directed from the conductor part 28 towards the inner wall of the combustion compartment 29 is not shielded by the grounding electrode 27 when the ion current is detected, and the electric field (lines of electric force) generated from the conductor part 28 can be distributed uniformly to an entire area in the combustion chamber 29.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug and an ignition / ion current detection device which also serve as a means (ion probe) for detecting an ion current generated when an air-fuel mixture burns in a combustion chamber of an internal combustion engine. It is.

[0002]

2. Description of the Related Art In recent years, attention has been paid to the point that ions are generated when an air-fuel mixture burns in a combustion chamber of an internal combustion engine, and a technology has been developed for detecting this ion current and detecting a combustion state such as misfire or knocking. Have been. Many ion probes that detect the ion current also serve as spark plugs due to cost and assembly restrictions.

[0003]

However, since the ion current detected through the spark plug is weak, the influence of noise is large. For this reason, in order to increase the detection accuracy of the ion current, it is necessary to considerably increase the accuracy of the ion current detection circuit side. It was difficult.

The reason that the ion current detected by the conventional spark plug becomes weak is considered as follows. In the conventional spark plug, as shown in FIG. 14, an L-shaped ground electrode 12 protrudes toward the combustion chamber 13 so as to cover below the center electrode 11, and a large electric field is applied between the center electrode 11 and the ground electrode 12. A gradient is formed, and the combustion chamber 1
An electric field directed toward the inner wall 3 is also formed, but the electric field gradient is reduced at the portion (C portion) on the back side of the ground electrode 12. This is because an electric field (line of electric force) from the center electrode 11 toward the inner wall of the combustion chamber 13 is shielded by the ground electrode 12. In this relation, the gradient of the electric field from the center electrode 11 toward the inner wall of the combustion chamber 13 is increased only in a portion not shielded by the ground electrode 12 (portion B). At the time of combustion, ions are generated in the entire region of the combustion chamber 13. To collect and detect the ions at the center electrode 11, it is necessary to move the ions to the center electrode 11 by an electric field gradient.
Therefore, ions generated in the portion B having a large electric field gradient can be collected and detected by the center electrode 11, but ions generated in the portion C behind the ground electrode 12 having a small electric field gradient cannot be detected. There is a high possibility that it will disappear naturally. For this reason, only a part of the ions generated in the combustion chamber 13 during combustion can be taken out as a current, and the ion current detection signal becomes small.

[0005] The present invention has been made in view of such circumstances, and the object of the present invention is to collect ions generated in the combustion chamber during combustion efficiently from a wide area of the combustion chamber to the center electrode and obtain an ion current. An object of the present invention is to provide a spark plug and an ignition / ion current detection device capable of detecting the ion current and increasing the ion current detection signal.

[0006]

According to a first aspect of the present invention, there is provided a spark plug according to the present invention, wherein a part of a center electrode or a conductor provided on the center electrode is provided in a combustion chamber rather than a ground electrode. It is configured to protrude. As described above, when a part (or a conductor) of the center electrode is made to protrude into the combustion chamber from the ground electrode, an electric field shield of the ground electrode against an electric field from the center electrode (or the conductor) toward the inner wall of the combustion chamber when an ion current is detected. The effect is weakened. As a result, the electric field generated from the center electrode (or conductor) can be uniformly distributed over a wide area of the combustion chamber, and ions generated in the combustion chamber during combustion are efficiently collected at the center electrode from the wide area of the combustion chamber. Can be detected as an ion current. As a result, the ion current extracted through the center electrode can be made larger than before, the influence of noise can be reduced, the detection accuracy of the ion current can be improved, and the design standard of the ion current detection circuit is relaxed. And cost can be reduced accordingly.

Further, the ground electrode may be formed to be short, the center electrode may be formed to be long and bent in an L-shape, and a tip portion thereof may be opposed to the ground electrode. That is, the conventional general spark plug is shown in FIG.
As shown in the figure, the center electrode is short and the ground electrode is bent in an L shape. On the contrary, the center electrode is shorter than the ground electrode by bending the center electrode in an L shape. The structure protruding into the combustion chamber can be easily realized, and the area of the center electrode for detecting the ion current can be increased. Thus, the effect of increasing the ion current extracted through the center electrode can be obtained.

By the way, in the conventional general spark plug shown in FIG. 14, a high negative voltage is applied to the center electrode at the time of ignition.
Since the area of the center electrode is larger than the area of the ground electrode, it is preferable to apply a positive high voltage to the center electrode by the ignition circuit at the time of ignition to cause spark discharge. With this configuration, even when the center electrode is bent in an L-shape, discharge starts at a low voltage, and sufficient ignition performance is secured without changing (strengthening) the withstand voltage characteristics of the ignition system circuit. be able to. In this case, similarly to the related art, if a positive voltage is applied to the center electrode by the ionic current detection circuit after the end of the spark discharge, the ionic current can be detected through the center electrode.

Further, a small gap is formed at the base or the middle of the ground electrode as in the ignition plug according to the fourth aspect of the present invention. A spark discharge may be made between the electrode and the center electrode. In this way, at the time of ion current detection, the portion of the ground electrode beyond the micro gap is insulated from the ground side by the micro gap and the electric field shielding effect is weakened. Even if the electric field protrudes into the combustion chamber from the electrode, the electric field generated from the center electrode can be uniformly distributed over a wide area of the combustion chamber.

[0010] Further, as in the spark plug of the fifth aspect, a structure may be employed in which a portion of the ground electrode other than the spark discharge portion is covered with an insulating layer. With this configuration, the portion of the ground electrode covered with the insulating layer (that is, the portion other than the spark discharge portion) has a weak electric field shielding effect. However, the electric field generated from the center electrode can be evenly distributed over a wide area of the combustion chamber even if it projects into the combustion chamber.

[0011]

[Embodiment (1)] An embodiment (1) of the present invention will be described below with reference to FIGS.
3 to 9 show various electrode structures of the ignition plug 21 used in the embodiment (1). As shown in FIG. 1, the ignition plug 21 has an insulator portion 22, and a center electrode 23 is provided at a lower center of the insulator portion 22 so as to protrude downward. The center electrode 23 is electrically connected to a terminal 24 provided at the upper end of the insulator 22.
A metal housing 25 is attached to the outer periphery of the lower half of the insulator portion 22 by caulking.
6 are formed. An L-shaped ground electrode 27 is welded to the lower end of the metal housing 25.
The tip of 7 is opposed to the lower end of the center electrode 23 with a gap for spark discharge therebetween. The ground electrode 27 is electrically connected to the cylinder head (ground side) via the metal housing 25.

In the first embodiment shown in FIGS. 1 and 3, a U-shaped conductor 28 is fixed to the center electrode 23 by welding or the like, and this conductor 28 projects from the ground electrode 27 into the combustion chamber 29. Thus, the conductor 28 covers the ground electrode 27 from below. Note that the conductor portion 28 is
And may be formed integrally.

Next, the configurations of the ignition circuit 30 and the ion current detection circuit 31 will be described with reference to FIG. Ignition coil 3
One end of the primary coil 33 is connected to a power supply terminal (+ B), and the other end of the primary coil 33 is connected to the collector of a power transistor 34 for controlling ignition. One end of the secondary coil 35 of the ignition coil 32 is connected to the center electrode 23 of the ignition plug 21, and the other end of the secondary coil 35 is
It is connected to the ground side via two Zener diodes 36 and 37.

The two Zener diodes 36 and 37 are connected in series in opposite directions, a capacitor 38 is connected in parallel to one Zener diode 36, and an ion current detecting resistor 39 is connected in parallel to the other Zener diode 37. I have. Capacitor 38 and ion current detection resistor 3
9 is applied to the inverting amplifier circuit 4 via the resistor 40.
1 is input to the inverting input terminal (-) and is inverted and amplified.
The ion current detection circuit 31 includes a zener diode 36,
37, a capacitor 38, an ion current detection resistor 39, an inverting amplifier circuit 41, and the like.

During operation of the engine, the engine control circuit 42
The power transistor 34 is turned on / off by the rise / fall of the ignition signal IGt output from the power supply. When the power transistor 34 is turned on, a battery (not shown)
When the power transistor 34 is turned off, the primary current of the primary coil 33 is cut off, a high voltage is electromagnetically induced in the secondary coil 35, and a negative high voltage is applied to the ignition plug 21. , A spark discharge is generated between the center electrode 23 and the ground electrode 27.

At this time, a spark discharge current flows from the ground electrode 27 to the center electrode 23, charges the capacitor 38 via the secondary coil 35, and simultaneously sets the Zener diodes 36, 3
It flows to the earth side via 7. After the capacitor 38 is charged, the ion current detection circuit 31 is driven using the charging voltage of the capacitor 38 regulated by the Zener voltage of the Zener diode 36 as a power supply, and the ion current is detected as follows.

After the end of the spark discharge, a positive voltage is applied to the center electrode 23 of the ignition plug 21 and the conductor 28 by the charging voltage of the capacitor 38, and an electric field from the conductor 28 to the inner wall of the combustion chamber 13 is generated in the combustion chamber 29. It is formed. As a result, negative ions and the like (correctly positive and negative ions and electrons, which move in the opposite direction due to charge polarity) generated when the air-fuel mixture burns in the combustion chamber 29 move toward the conductor portion 28 by the electric field gradient. Then, it is collected by the conductor 28 (the center electrode 23). The capacitor 38 is discharged according to the charge of the negative ions collected in this manner, and the ionic current flows from the ground to the ionic current detecting resistor 39. At this time, the input potential Vin of the inverting amplifier circuit 41 changes according to the change of the ion current flowing through the ion current detecting resistor 39, and the inverting amplifier circuit 4
A voltage corresponding to the ion current is output to the engine control circuit 42 from the output terminal 1 as an ion current detection signal. An ion current is detected from the output voltage of the inverting amplifier circuit 41, and misfire, knocking, and the like are detected from the ion current.

In the first embodiment shown in FIGS. 1 and 3, the U-shaped conductor 28 provided on the center electrode 23 projects into the combustion chamber 29 beyond the ground electrode 27, and the conductor 28 is
7 is covered from below, the electric field from the conductor 28 toward the inner wall of the combustion chamber 29 is not shielded by the ground electrode 27 when the ion current is detected, and the conductor 2
The electric field (lines of electric force) generated from the combustion chamber 29 can be uniformly distributed over substantially the entire area of the combustion chamber 29, and the combustion chamber 29
The ions generated in the inside can be efficiently collected from almost the entire area of the combustion chamber 29 to the center electrode 23 and detected as an ion current. As a result, the output (ion current detection signal) of the ion current detection circuit 31 can be made larger than in the past, the influence of noise can be reduced, and the detection accuracy of the ion current can be increased. The design standard of the detection circuit 31 can be relaxed, and the cost can be reduced accordingly.

In the second embodiment shown in FIG. 4, two conductors 43 opposed to each other with the ground electrode 27 interposed therebetween are provided on the center electrode 23, and these two conductors 43 are connected to the ground electrode 27. And project downward into the combustion chamber 29.

In the third embodiment shown in FIG.
And two conductor portions 44 opposed to each other with the ground electrode 27 interposed therebetween are provided sideways, and these two conductor portions 44 are connected to the ground electrode 27.
Rather, it projects laterally into the combustion chamber 29.

In the fourth embodiment shown in FIG.
A ring-shaped conductor 45 is provided at the lower end of the ring-shaped conductor 45. The tip of the ground electrode 27 is inserted into a hole of the ring-shaped conductor 45, and a spark is generated by a gap between the inner edge of the conductor 45 and the ground electrode 27 during ignition. Generates discharge. Also in this case, the conductor portion 45 is in a state of protruding from the ground electrode 27 into the combustion chamber 29.

In the fifth embodiment shown in FIG.
Is formed shorter than before, and the center electrode 23 is formed to be longer downward, so that the tip of the ground electrode 27 is opposed to the outer peripheral surface of the center electrode 23 from the lateral direction. A spark discharge is generated between and. Further, a circular conductor 46 is provided at the lower end of the center electrode 23, and the conductor 46 projects from the ground electrode 27 into the combustion chamber 29.

In the sixth embodiment shown in FIG.
A ring portion 48 is provided horizontally at the tip of the
The center electrode 23 is inserted through the hole 8 so that the center electrode 23
And a spark discharge is generated between the ring portion 48 and the ring portion 48. Furthermore,
A circular conductor 47 is provided at the lower end of the center electrode 23, and the conductor 47 is separated from the combustion chamber 2 by the ground electrode 27 (ring 48).
9.

In the seventh embodiment shown in FIG. 9, similarly to the sixth embodiment, a ring portion 48 is provided horizontally at the tip of the ground electrode 27, and the center electrode 23 is inserted through a hole in the ring portion 48. The lower end of the center electrode 23 projects into the combustion chamber 29 from the ground electrode 27 (ring portion 48). That is,
The seventh embodiment of FIG. 9 is different from the sixth embodiment of FIG. 8 only in that a circular conductor 47 is not provided at the lower end of the center electrode 23.

In each of the embodiments shown in FIGS. 4 to 9 described above, as in the first embodiment shown in FIG. 3, a part of the center electrode 23 or the conductor portions 43 to 47 are located in the combustion chamber more than the ground electrode 27. 29, the electric field shielding effect of the ground electrode 27 is weakened, and the electric field can be uniformly distributed over a wide area of the combustion chamber 29.
The ions generated in the inside can be efficiently collected on the center electrode 23 from a wide range of the combustion chamber 29 and detected as an ion current.

[Embodiment (2)] In an ignition plug 50 according to an embodiment (2) of the present invention shown in FIG. 10, a protruding ground electrode 51 is formed short and fixed to the lower end of a metal housing 25 by welding. , The center electrode 52 is formed long and
The center electrode 52 is bent so as to face the ground electrode 51 with a spark discharge gap therebetween.
As a result, the center electrode 52 protrudes into the combustion chamber more than the ground electrode 51, and the center electrode 52 covers the ground electrode 51 from below.

In the conventional general spark plug shown in FIG. 14, a high negative voltage is applied to the center electrode 11 at the time of ignition. However, in the spark plug 50 of this embodiment (2), Since the area of the center electrode 52 is larger than the area of the ground electrode 51, a spark discharge is generated by applying a positive high voltage to the center electrode 52 by the ignition circuit 53 at the time of ignition. By doing so, it is possible to generate a spark discharge at a lower voltage than when a negative high voltage is applied to the center electrode 52, and it is possible to secure sufficient ignition performance. In the present embodiment (2), the secondary coil 35 of the ignition coil 32
Is connected to the ground side, and the other end of the secondary coil 35 is connected to a spark plug 50 through a diode 54 for preventing backflow.
Terminal 24.

On the other hand, the ion current detection circuit 55 is connected in parallel with the ignition plug 50, and is configured by connecting a protection diode 56, a bias power supply 57 and an ion current detection resistor 58 in series. This ion current detection circuit 55
After the end of the spark discharge, a positive voltage is applied to the center electrode 57 by the bias power supply 57, and the same as in the embodiment (1),
An ion current flowing through the ion current detection resistor 58 is detected. Incidentally, as in the embodiment (1), the voltage of the ion current detection resistor 58 may be amplified by an inverting amplifier circuit to extract an ion current detection signal.

In the embodiment (2) described above,
Since the center electrode 52 projects beyond the ground electrode 51 into the combustion chamber and the center electrode 52 covers the ground electrode 51 from below, the electric field from the center electrode 52 toward the combustion chamber wall is shielded by the ground electrode 51. Will not be
Ions generated in the combustion chamber during combustion can be efficiently collected on the center electrode 23 from a wide range of the combustion chamber and detected as an ion current.

[Embodiment (3)] In the spark plug 60 according to the embodiment (3) of the present invention shown in FIGS. 11 and 12, a minute gap 62 is formed at the base or middle of the ground electrode 61, and the minute gap 62 is formed. The outer periphery of 62 is covered with a heat-resistant insulator 63 such as a ceramic, and the ground electrode 61 is fixed to the metal housing 25 side by the heat-resistant insulator 63.
In this case, the minute gap 62 is formed shorter than the gap 64 between the ground electrode 61 and the center electrode 23. At the time of ignition, a high negative voltage is applied to the center electrode 23, and at the time of detecting an ionic current, a positive voltage is applied to the center electrode 23.

In this case, at the time of spark discharge, the ground electrode 61
The high voltage current flowing through the small gap 62 is caused to flow by discharge, and a spark discharge is caused between the ground electrode 61 and the center electrode 23. After the end of the spark discharge, a positive voltage is applied to the center electrode 23 by the ionic current detection circuit to detect the ionic current. At this time, the ground electrode 61 is insulated from the ground side by the minute gap 62 and the electric field shielding effect is weakened. For,
Even if the ground electrode 61 covers the center electrode 23 from below,
As shown in FIG. 12, the electric field generated from the center electrode 23 can be uniformly distributed over a wide area of the combustion chamber 29, and ions generated in the combustion chamber 29 during combustion can be efficiently centered from the wide area of the combustion chamber. It can be collected at the electrode 23 and detected as an ion current.

[Embodiment (4)] In the spark plug 70 of an embodiment (4) of the present invention shown in FIG. 13, the portion of the ground electrode 27 other than the spark discharge portion 27a closest to the center electrode 23 is made of ceramic or the like. With a heat-resistant insulating layer 71. In this structure, a portion of the ground electrode 27 covered with the insulating layer 71 (that is, a portion other than the spark discharge portion 27a)
Since the electric field shielding effect is weakened by the insulating layer 71, even when the ground electrode 27 covers the center electrode 23 from below, the electric field generated from the center electrode 23 It can be uniformly distributed over a wide range.

[Brief description of the drawings]

FIG. 1 is a view showing an electric field distribution in a combustion chamber when an ignition plug and an ion current are detected according to an embodiment (1) of the present invention.

FIG. 2 is a circuit diagram showing a configuration of an ignition circuit and an ion current detection circuit.

3A is a front view showing the electrode structure of the spark plug of the first embodiment, and FIG. 3B is a bottom view of the same.

4A is a front view showing an electrode structure of a spark plug according to a second embodiment, FIG. 4B is a bottom view thereof, and FIG. 4C is a perspective view thereof.

5A is a front view showing an electrode structure of a spark plug according to a third embodiment, FIG. 5B is a bottom view thereof, and FIG. 5C is a perspective view thereof.

6A is a front view showing an electrode structure of a spark plug according to a fourth embodiment, FIG. 6B is a bottom view thereof, and FIG. 6C is a perspective view thereof.

7A is a front view showing an electrode structure of a spark plug according to a fifth embodiment, FIG. 7B is a bottom view thereof, and FIG. 7C is a perspective view thereof.

8A is a front view showing an electrode structure of a spark plug according to a sixth embodiment, FIG. 8B is a bottom view thereof, and FIG. 8C is a perspective view thereof.

9A is a front view showing an electrode structure of a spark plug according to a seventh embodiment, FIG. 9B is a bottom view thereof, and FIG. 9C is a perspective view thereof.

FIG. 10 is a diagram showing a configuration of an ignition plug, an ignition circuit, and an ion current detection circuit according to an embodiment (2) of the present invention.

FIG. 11 is a longitudinal sectional front view showing an electrode structure of a spark plug according to an embodiment (3) of the present invention.

FIG. 12 is a diagram showing an electric field distribution in a combustion chamber when an ion current is detected in the embodiment (3) of the present invention.

FIG. 13 is a longitudinal sectional front view showing an electrode structure of a spark plug according to an embodiment (4) of the present invention.

FIG. 14 is a diagram showing a conventional spark plug and an electric field distribution in a combustion chamber when an ion current is detected.

[Explanation of symbols]

Reference numeral 21: spark plug, 22: insulator part, 23: center electrode, 2
4 ... Terminal, 25 ... Metal housing, 27 ... Ground electrode, 2
8 conductor part, 29 combustion chamber, 30 ignition circuit, 31 ion current detection circuit, 32 ignition coil, 33 primary coil, 35 secondary coil, 38 capacitor, 39 ion current detection resistor, 41 ... inverting amplifier circuits, 43 to 47 ... conductor parts, 48 ... ring parts, 50 ... ignition plugs, 51 ... ground electrodes, 52 ... center electrodes, 53 ... ignition circuits, 55 ... ion current detection circuits, 57 ... bias power supplies, 58 ... Ion current detection resistor, 60 ... Spark plug, 61 ... Ground electrode, 62 ...
Micro gap, 63: heat resistant insulator, 70: spark plug, 71: insulating layer.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Naoki Kokubo 1-1-1, Showa-cho, Kariya-shi, Aichi, Japan

Claims (5)

[Claims] An ignition plug, which also serves as a means for detecting an ionic current generated when an air-fuel mixture burns in a combustion chamber of an internal combustion engine, wherein a part of a center electrode or a conductor provided on the center electrode is grounded. A spark plug protruding into the combustion chamber. 2. The ground electrode according to claim 1, wherein the ground electrode is formed short, the center electrode is formed long and bent into an L shape, and a tip portion thereof is opposed to the ground electrode. Spark plug. 3. The ignition / ion current detection device using the ignition plug according to claim 2, wherein an ignition circuit for applying a high positive voltage to the center electrode to perform a spark discharge at the time of ignition, and to end the spark discharge. An ignition / ion current detection device comprising: an ion current detection circuit for applying a positive voltage to the center electrode to detect an ion current. 4. A spark plug, which also serves as a means for detecting an ionic current generated when an air-fuel mixture burns in a combustion chamber of an internal combustion engine, comprising: a high voltage flowing through the ground electrode at the base or midway of the ground electrode during ignition; A spark plug characterized by forming a minute gap through which current flows by discharging. 5. A spark plug, which also serves as a means for detecting an ionic current generated when an air-fuel mixture burns in a combustion chamber of an internal combustion engine, wherein a portion of the ground electrode other than a spark discharge portion is covered with an insulating layer. A spark plug characterized by the above.