JP2013185557A - Ignition device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ignition device for an internal combustion engine capable of broadening a condition that can generate arc discharge in a discharge gap of an ignition plug.SOLUTION: An ignition device 1 is installed in an internal combustion engine 5 and includes an ignition plug 2 having a discharge gap 20, an arc discharge power source 31, an arc discharge control means 41, a streamer discharge power source 32, and a streamer discharge control means 42. The ignition device 1 is configured to control in such a manner that, under a basic condition that arc discharge cannot be induced in the discharge gap 20 only if an arc discharge voltage is applied to the discharge gap 20 of the ignition plug 2, and immediately before arc discharge is induced by applying an arc discharge voltage to the discharge gap 20 of the ignition plug 2 by the arc discharge control means 41, streamer discharge is induced by applying a streamer discharge voltage to the discharge gap 20 of the ignition plug 2 by the streamer discharge control means 42.

Description

  The present invention relates to an ignition device including an ignition plug used as an ignition means in an internal combustion engine such as an automobile.

  2. Description of the Related Art Conventionally, an ignition device having an ignition plug used as an ignition means in an internal combustion engine such as an automobile is known. The spark plug in the ignition device is attached to the combustion chamber of the internal combustion engine, and forms a discharge gap between the center electrode and the ground electrode. Then, by applying a voltage to the discharge gap of the spark plug to generate arc discharge or the like, an air-fuel mixture (a mixture of air and fuel) formed in the vicinity of the spark plug is ignited.

  Patent Document 1 discloses an ignition device that generates streamer discharge immediately before arc discharge in order to enhance the ignitability of the spark plug by arc discharge. In this ignition device, many active species can be generated by streamer discharge, and the air-fuel mixture can be easily ignited. Thereby, the ignitability by the arc discharge immediately after streamer discharge can be improved, and flame propagation can be promoted.

JP 2009-47149 A

In recent years, in an internal combustion engine such as a gasoline engine of an automobile, high supercharging and high compression ratio have been promoted for fuel saving, and the environmental pressure (pressure in the combustion chamber of the internal combustion engine at the ignition timing) is very high. It has become.
In addition, when performing lean combustion for fuel saving, there is a demand to increase the discharge gap of the spark plug in order to improve ignitability.

  However, when the environmental pressure is high, particularly when the discharge gap of the spark plug is large, arc discharge may not be normally generated in the discharge gap. That is, arc discharge may occur in a portion other than the discharge gap. For this reason, the ignitability is lowered, and it is difficult to apply under conditions where the environmental pressure is high. Further, it cannot meet the demand for increasing the discharge gap.

  The present invention has been made in view of such a background, and an object of the present invention is to provide an ignition device for an internal combustion engine capable of expanding the conditions under which arc discharge can be normally performed in the discharge gap of the spark plug.

One aspect of the present invention is a spark plug disposed in an internal combustion engine and having a discharge gap;
An arc discharge power source for applying an arc discharge voltage to the discharge gap of the spark plug;
Arc discharge control means for controlling the timing at which the arc discharge is generated by applying the arc discharge voltage to the discharge gap of the spark plug from the arc discharge power supply;
A streamer discharge power source for applying a streamer discharge voltage to the discharge gap of the spark plug;
Streamer discharge control means for controlling when the streamer discharge is generated by applying the streamer discharge voltage from the streamer discharge power source to the discharge gap of the spark plug;
Under reference conditions in which arc discharge cannot be generated in the discharge gap simply by applying the arc discharge voltage to the discharge gap of the spark plug, the arc discharge control means causes the discharge gap of the spark plug to be in the discharge gap. Immediately before applying the arc discharge voltage to generate the arc discharge, the streamer discharge control means applies the streamer discharge voltage to the discharge gap of the spark plug to generate the streamer discharge. An ignition device for an internal combustion engine characterized by the above.

In the above ignition device, the arc discharge is not generated in the discharge gap only by applying the arc discharge voltage to the discharge gap of the spark plug. In addition, streamer discharge is generated in the spark plug by the streamer discharge control means.
That is, as a result of diligent research, the present inventor has performed a discharge by performing a streamer discharge immediately before the arc discharge, even under the above-mentioned reference conditions in which it is difficult to normally generate an arc discharge in the discharge gap of the spark plug. It has been found that arc discharge can be normally generated in the gap.

  More specifically, streamer discharge is characterized by being easier to normally discharge in the discharge gap than when arc discharge, for example, when the intake pressure or in-cylinder pressure of the internal combustion engine is high or when the discharge gap is large. . Utilizing this fact, the streamer discharge is performed immediately before the arc discharge under the above-mentioned reference condition in which it is difficult to normally generate the arc discharge in the discharge gap of the spark plug. By doing so, streamer discharge can be generated in the discharge gap, and an electrical path can be formed in the discharge gap. Therefore, the arc discharge performed immediately after the streamer discharge is likely to occur along an electrical path formed in the discharge gap by the streamer discharge. That is, it is possible to easily generate arc discharge in the discharge gap.

  As a result, even under the above-described reference conditions in which it is difficult to normally generate arc discharge in the discharge gap of the spark plug, by performing streamer discharge immediately before the arc discharge, the arc discharge is generated normally in the discharge gap. be able to. In other words, the conditions under which arc discharge can be generated in the discharge gap of the spark plug can be expanded. As a result, it is possible to operate under conditions of high environmental pressure such as high supercharging and high compression ratio. Further, when performing lean combustion, it is possible to meet the demand for expanding the discharge gap for improving ignitability.

  In this way, it is possible to provide an ignition device for an internal combustion engine that can expand the conditions under which arc discharge can be generated in the discharge gap of the spark plug.

FIG. 3 is an explanatory diagram illustrating a configuration of an ignition device in the first embodiment. Explanatory drawing which expands and shows the discharge gap periphery of a spark plug in Example 1. FIG. Explanatory drawing which shows a mode that the streamer discharge has generate | occur | produced normally in the discharge gap of the ignition plug in Example 1. FIG. Explanatory drawing which shows a mode that the arc discharge has generate | occur | produced normally in the discharge gap of the ignition plug in Example 1. FIG. The graph which shows the relationship between the discharge time and discharge current of streamer discharge and arc discharge in Example 1. FIG. 2 is a flowchart showing control of arc discharge and streamer discharge of a spark plug in the first embodiment. Explanatory drawing which shows a mode that the arc discharge has generate | occur | produced in parts other than the discharge gap of a spark plug in Example 1. FIG. 7 is a graph showing the relationship between the crank angle of the engine and the in-cylinder pressure in Example 2. The graph which shows the flying ratio of Example E and Comparative Example C in Example 3. FIG. The graph which shows the relationship between the rotation speed of an engine and BMEP in Example 4. FIG. FIG. 9 is an explanatory diagram showing a discharge gap in Example 5. The graph which shows the relationship between the time T and the flying ratio in Example 5. FIG.

  In the ignition device, a reference condition in which arc discharge cannot be generated in the discharge gap simply by applying the arc discharge voltage to the discharge gap of the spark plug is, for example, arc discharge in the discharge gap of the spark plug. This refers to a condition in which arc discharge does not occur in the discharge gap even when application voltage is applied, and arc discharge may occur in portions other than the discharge gap.

The reference condition may include that the intake pressure of the internal combustion engine is 0.1 MPa or more at an ignition timing by the ignition plug.
Under such conditions, there is a case where arc discharge cannot be normally generated in the discharge gap of the spark plug. Therefore, by performing the streamer discharge immediately before the arc discharge, it becomes possible to normally generate the arc discharge in the discharge gap.

In addition, when the intake pressure of the internal combustion engine exceeds 0.2 MPa, there is a risk that it will be difficult to normally generate arc discharge in the discharge gap of the spark plug even if streamer discharge is performed immediately before arc discharge. is there.
Therefore, it is desirable that the intake pressure of the internal combustion engine be 0.2 MPa or less.

The intake pressure of the internal combustion engine is the pressure of air taken into the cylinder of the internal combustion engine. The intake pressure can be detected by, for example, an intake pressure sensor or an intake air amount sensor provided in an intake pipe (intake port).
Moreover, the numerical value of the intake pressure of the internal combustion engine is a gauge pressure in which the atmospheric pressure is zero.

The reference condition may include that an in-cylinder pressure of the internal combustion engine is 4 MPa or more at an ignition timing by the ignition plug.
Under such conditions, there is a case where arc discharge cannot be normally generated in the discharge gap of the spark plug. Therefore, by performing the streamer discharge immediately before the arc discharge, it becomes possible to normally generate the arc discharge in the discharge gap.

Further, when the in-cylinder pressure of the internal combustion engine exceeds 6 MPa, it may be difficult to normally generate arc discharge in the discharge gap of the spark plug even if streamer discharge is performed immediately before arc discharge.
Therefore, it is desirable that the in-cylinder pressure of the internal combustion engine be 6 MPa or less.

The in-cylinder pressure of the internal combustion engine is the pressure in the combustion chamber of the cylinder of the internal combustion engine. The in-cylinder pressure can be detected by, for example, an in-cylinder pressure sensor provided in the combustion chamber.
The numerical value of the in-cylinder pressure of the internal combustion engine is a gauge pressure where the atmospheric pressure is zero.

The reference condition may include that the size of the discharge gap of the spark plug is 0.9 mm or more (claim 4).
Under such conditions, there is a case where arc discharge cannot be normally generated in the discharge gap of the spark plug. Therefore, by performing the streamer discharge immediately before the arc discharge, it becomes possible to normally generate the arc discharge in the discharge gap.

Further, under the pressure condition in the internal combustion engine, for example, when the size of the discharge gap of the spark plug exceeds 1.3 mm, the discharge gap of the spark plug is not affected even if the streamer discharge is performed immediately before the arc discharge. In this case, it may be difficult to normally generate arc discharge.
Therefore, it is desirable that the size of the discharge gap of the spark plug is 1.3 mm or less.

The spark plug includes a center electrode, an insulator that holds the center electrode on the inside, and a mounting screw portion that holds the insulator on the inside and is screwed into the internal combustion engine on the outer peripheral surface. A ground electrode that forms a discharge gap between the housing and the center electrode is provided, and the reference condition may include that the screw diameter of the mounting screw portion is M12 or less ( Claim 5).
Under such conditions, since the insulation distance between the spark plug housing and the discharge gap is not sufficient, there is a case where the arc discharge cannot be normally generated in the discharge gap. Therefore, by performing the streamer discharge immediately before the arc discharge, it becomes possible to normally generate the arc discharge in the discharge gap.

In addition, the reference condition may include that the net average effective pressure of the internal combustion engine is equal to or greater than a predetermined threshold (Claim 6).
In this case, by setting the reference condition in advance based on the value of the net average effective pressure of the internal combustion engine, it is possible to easily control arc discharge and streamer discharge in the ignition device.

Moreover, the threshold value of the net average effective pressure of the internal combustion engine can be set, for example, by the following procedure. That is, for each value of the net average effective pressure of the internal combustion engine, only arc discharge is performed a predetermined number of times on the spark plug, and the relationship between the net average effective pressure of the internal combustion engine and the spark ratio is examined. Here, the flying ratio refers to the ratio of the number of times arc discharge has normally occurred in the discharge gap to the number of discharges of arc discharge. Then, the value of the net average effective pressure of the internal combustion engine in which the spark ratio changes from 100% to less than 100% is set as a threshold value.
Moreover, the threshold value of the net average effective pressure of the internal combustion engine can be set to 0.9 to 1.2 MPa, for example.

In addition, after the streamer discharge control means starts applying the streamer discharge voltage to the discharge gap of the spark plug, the arc discharge control means applies the arc discharge voltage to the discharge gap of the spark plug. The time T until the start is desirably 120 μsec or less (claim 7).
In this case, the probability of normal arc discharge occurring in the discharge gap of the spark plug can be increased.

The time T is desirably 60 μsec or less.
In this case, the probability of normal arc discharge occurring in the discharge gap of the spark plug can be further increased.

  The time T is when the streamer discharge control means starts to apply the streamer discharge voltage to the discharge gap of the spark plug and when the arc discharge control means starts to apply the arc discharge voltage to the spark plug discharge gap. And the time difference. Therefore, the time T is longer than the time for performing the streamer discharge.

Moreover, the time (discharge time) for generating the streamer discharge in the spark plug can be, for example, 10 to 500 nsec.
Moreover, the time (discharge time) for generating the arc discharge in the spark plug can be set to 0.3 msec or more, for example.

Preferably, the streamer discharge voltage applied to the discharge gap of the spark plug from the streamer discharge power source is 30 kV or more, and the half width of the voltage waveform is 100 nsec or less.
In this case, streamer discharge can be easily generated in the discharge gap by applying a short pulse high voltage from the streamer discharge power supply to the discharge gap of the spark plug.

In addition, the ignition device may be configured such that, under conditions other than the reference condition, the streamer discharge is performed immediately before the arc discharge control means applies the arc discharge voltage to the discharge gap of the ignition plug to generate the arc discharge. The control means can be configured not to generate the streamer discharge by applying the streamer discharge voltage to the discharge gap of the spark plug (claim 10).
In this case, streamer discharge is not performed immediately before arc discharge under conditions other than the above-described reference conditions, that is, conditions under which arc discharge can be normally generated in the discharge gap of the spark plug. Thereby, useless use of energy can be prevented.

Example 1
Embodiments of the ignition device for the internal combustion engine will be described with reference to the drawings.
As shown in FIG. 1, the ignition device 1 of this example is disposed in an internal combustion engine (engine) 5, and applies an arc discharge voltage to a spark plug 2 having a discharge gap 20 and a discharge gap 20 of the spark plug 2. An arc discharge power source 31 for controlling the arc discharge, and an arc discharge control means 41 for controlling the timing of generating an arc discharge by applying an arc discharge voltage to the discharge gap 20 of the spark plug 2 from the arc discharge power source 31; A streamer discharge power source 32 for applying a streamer discharge voltage to the discharge gap 20 and a timing for generating a streamer discharge by applying the streamer discharge voltage from the streamer discharge power source 32 to the discharge gap 20 of the spark plug 2. And a streamer discharge control means 42 for controlling.

As shown in the figure, under reference conditions in which arc discharge cannot be generated in the discharge gap 20 simply by applying an arc discharge voltage to the discharge gap 20 of the spark plug 2, the arc discharge control means 41 causes the spark plug 2 to Just before the arc discharge voltage is applied to the discharge gap 20 to generate the arc discharge, the streamer discharge control means 42 applies the streamer discharge voltage to the discharge gap 20 of the spark plug 2 to generate the streamer discharge. ing.
This will be described in detail below.

  As shown in FIG. 1, in the ignition device 1 of this example, each cylinder (cylinder) 50 of the engine 5 that is a gasoline engine includes a cylinder head 51, a cylinder block 52, and a piston 53 that reciprocates in the cylinder block 52. It has. A combustion chamber 54 is formed in a space surrounded by the cylinder head 51, the cylinder block 52 and the piston 53.

  The cylinder head 51 is formed with an intake port 511 for intake to the combustion chamber 54 and an exhaust port 512 for exhaust from the combustion chamber 54. The cylinder head 51 is provided with an intake valve 551 that opens and closes the intake port 511 and an exhaust valve 552 that opens and closes the exhaust port 512. An intake pressure sensor 56 that detects the intake pressure of the engine 5 is attached to the intake port 511.

  Further, the ignition plug 2 that generates arc discharge and streamer discharge in the combustion chamber 54 is attached to the cylinder head 51. The spark plug 2 is attached in a state where the tip portion where the discharge gap 20 is formed is exposed in the combustion chamber 54. In addition, an injector (combustion injection valve) 57 that injects gasoline fuel into the combustion chamber 54 is attached to the cylinder head 51.

  As shown in FIG. 2, the spark plug 2 includes a center electrode 21, an insulator 22 that holds the center electrode 21 inside, and an insulator 22 that holds the insulator 22 inside and is screwed into the cylinder head 51 of the cylinder 50 of the gasoline engine 5. The housing 23 is formed with a fitting screw portion 231 formed on the outer peripheral surface thereof, and a ground electrode 24 that forms a discharge gap 20 between the center electrode 21 and the housing 23. The screw diameter of the mounting screw portion 231 of the housing 23 is M12.

  The ground electrode 24 has a standing portion 241 that stands from the tip portion of the housing 23 and a facing portion 242 that faces the tip portion of the center electrode 21 in the axial direction. A discharge gap 20 is formed between the distal end portion of the center electrode 21 and the facing portion 242 of the ground electrode 24. The size G of the discharge gap 20 is the distance between the tip of the center electrode 21 and the facing portion 242 of the ground electrode 24, which is 1.1 mm.

  As shown in FIG. 1, the spark plug 2 is connected to an arc discharge power supply 31 and a streamer discharge power supply 32. The arc discharge power supply 31 and the streamer discharge power supply 32 are connected to an ECU (engine control unit) 4 having functions as arc discharge control means 41 and streamer discharge control means 42. The intake pressure sensor 56 is connected to the ECU 4. The arc discharge power supply 31, the streamer discharge power supply 32, and the ECU 4 are connected to the battery 10.

  The ignition device 1 is connected to the discharge gap 20 of the ignition plug 2 (arc discharge voltage, streamer discharge voltage) by the ECU 4 (arc discharge control means 41, streamer discharge control means 42) at the ignition timing of the ignition plug 2. Is applied to generate a discharge (arc discharge, streamer discharge), and an air-fuel mixture (a mixture of air and fuel) formed in the vicinity of the spark plug 2 can be ignited. The air-fuel mixture is formed by mixing the air introduced into the combustion chamber 54 of the engine 5 and the fuel injected by the injector 57.

  Further, the ignition device 1 is controlled by the ECU 4 (arc discharge control means 41) under a reference condition in which an arc discharge cannot be generated in the discharge gap 20 only by applying an arc discharge voltage to the discharge gap 20 of the spark plug 2. Immediately before the arc discharge voltage is applied to the discharge gap 20 of the spark plug 2 to generate the arc discharge, the streamer discharge voltage is applied to the discharge gap 20 of the spark plug 2 by the ECU 4 (streamer discharge control means 42). It is configured to generate a discharge. That is, as shown in FIG. 3, after performing streamer discharge (S in the figure), arc discharge (A in the figure) is performed as shown in FIG.

Here, as shown in FIG. 7, the reference condition is that arc discharge does not occur in the discharge gap 20 even when an arc discharge voltage is applied to the discharge gap 20 of the spark plug 2, and in other portions than the discharge gap 20. A condition that may cause arc discharge.
The reference condition of this example is that the intake pressure of the engine 5 is 0.1 MPa or more at the ignition timing by the spark plug 2.

As shown in FIG. 5, the ECU 4 (streamer discharge control means 42) starts applying the streamer discharge voltage to the discharge gap 20 of the spark plug 2 and then the ECU 4 (arc discharge control means 41) discharges the spark plug 2. The time T until the start of application of the arc discharge voltage to the gap 20 is 120 μsec or less. The time T may be 60 μsec or less.
The streamer discharge voltage applied to the discharge gap 20 of the spark plug 2 from the streamer discharge power supply 32 is 30 kV or more, and the half width of the voltage waveform is 100 nsec or less.

  In addition, the ignition device 1 uses a discharge gap of the spark plug 2 by the ECU 4 (arc discharge control means 41) under conditions other than the above-described reference conditions (the intake pressure of the engine 5 is less than 0.1 MPa at the ignition timing by the spark plug 2). Immediately before the arc discharge voltage is applied to 20 and the arc discharge is generated, the streamer discharge voltage is generated by applying the streamer discharge voltage to the discharge gap 20 of the spark plug 2 by the ECU 4 (streamer discharge control means 42). It is configured not to do. That is, only the arc discharge is performed without performing the streamer discharge immediately before the arc discharge.

Next, control of arc discharge and streamer discharge in the ignition device 1 of this example will be described.
As shown in FIG. 6, when the engine 5 is started, streamer discharge is performed immediately before arc discharge is performed in the spark plug 2. That is, after performing streamer discharge in the spark plug 2, arc discharge is performed (step S1).

  As shown in the figure, when the engine 5 is in operation, the ECU 4 determines whether or not the above-mentioned reference condition is met at the ignition timing by the spark plug 2. That is, it is determined whether the intake pressure of the engine 5 detected by the intake pressure sensor 56 attached to the intake port 511 of the engine 5 is less than the threshold value P1 (= 0.1 MPa) (step S2).

As shown in the figure, when the intake pressure of the engine 5 is less than the threshold value P1, the streamer discharge is not performed immediately before the arc discharge is performed in the spark plug 2. That is, only arc discharge is performed in the spark plug 2 (step 3).
When the intake pressure of the engine 5 is equal to or greater than the threshold value P1, streamer discharge is performed immediately before arc discharge is performed at the spark plug 2. That is, after performing streamer discharge in the spark plug 2, arc discharge is performed (step 4).

Next, the effect in the ignition device 1 of this example is demonstrated.
In the ignition device 1 of this example, the arc discharge control means 41 (ECU 4) is used under a reference condition in which an arc discharge cannot be generated in the discharge gap 20 only by applying an arc discharge voltage to the discharge gap 20 of the spark plug 2. Thus, the streamer discharge control means 42 (ECU 4) causes the spark plug 2 to generate streamer discharge immediately before the arc discharge is generated in the spark plug 2.
That is, as a result of earnest research, the present inventor has performed a streamer discharge immediately before the arc discharge even under the above-mentioned reference condition in which it is difficult to normally generate the arc discharge in the discharge gap 20 of the spark plug 2. It has been found that arc discharge can be normally generated in the discharge gap 20.

  More specifically, streamer discharge is characterized in that it is easy to normally discharge in the discharge gap 20 even when the intake pressure of the engine 5 is higher than arc discharge. Utilizing this fact, the streamer discharge is performed immediately before the arc discharge under the above-mentioned reference condition in which it is difficult to normally generate the arc discharge in the discharge gap 20 of the spark plug 2. By doing so, streamer discharge can be generated in the discharge gap 20 and an electrical path can be formed in the discharge gap 20. Therefore, the arc discharge performed immediately after the streamer discharge is likely to occur along the electrical path formed in the discharge gap 20 by the streamer discharge. That is, it is possible to easily generate arc discharge normally in the discharge gap 20.

  As a result, even under the above-described reference conditions in which it is difficult to normally generate arc discharge in the discharge gap 20 of the spark plug 2, by performing streamer discharge immediately before the arc discharge, Can be generated. In other words, the conditions under which arc discharge can be generated in the discharge gap 20 of the spark plug 2 can be expanded. As a result, it is possible to operate under conditions of high environmental pressure such as high supercharging and high compression ratio. Further, when performing lean combustion, it is possible to meet the demand for expanding the discharge gap for improving ignitability.

  Further, in this example, the reference condition includes that the intake pressure of the engine 5 is 0.1 MPa or more at the ignition timing by the spark plug 2. Under such conditions, there is a case where arc discharge cannot be normally generated in the discharge gap 20 of the spark plug 2. Therefore, it is possible to normally generate arc discharge in the discharge gap 20 by performing streamer discharge immediately before arc discharge.

In addition, after the streamer discharge control means 42 (ECU 4) starts applying the streamer discharge voltage to the discharge gap 20 of the spark plug 2, the arc discharge control means 41 (ECU 4) applies the arc discharge to the discharge gap 20 of the spark plug 2. The time T until the start of voltage application is 120 μsec or less. Thereby, it is possible to increase the probability of normal arc discharge occurring in the discharge gap 20 of the spark plug 2.
Further, the time T can be set to 60 μsec or less. Thereby, the probability that the arc discharge is normally generated in the discharge gap 20 of the spark plug 2 can be further increased.

  The streamer discharge voltage applied to the discharge gap 20 of the spark plug 2 from the streamer discharge power supply 32 is 30 kV or more, and the half width of the voltage waveform is 100 nsec or less. Therefore, a short pulse high voltage is applied from the streamer discharge power supply 32 to the discharge gap 20 of the spark plug 2. Thereby, streamer discharge can be easily generated in the discharge gap 20.

  Further, under conditions other than the above-mentioned reference conditions, the igniter 1 has a streamer immediately before the arc discharge control means 41 (ECU 4) applies an arc discharge voltage to the discharge gap 20 of the spark plug 2 to generate arc discharge. The discharge control means 42 (ECU) is configured not to generate a streamer discharge by applying a streamer discharge voltage to the discharge gap 20 of the spark plug 2. For this reason, streamer discharge is not performed immediately before arc discharge under conditions other than the above-described reference conditions, that is, under conditions where arc discharge can be normally generated in the discharge gap 20 of the spark plug 2. Thereby, useless use of energy can be prevented.

  Thus, according to this example, it is possible to provide the ignition device 1 for an internal combustion engine that can expand the conditions under which arc discharge can be generated in the discharge gap 20 of the spark plug 2.

  In this example, the reference condition is determined based on the intake pressure (0.1 MPa or more) of the engine 5 at the ignition timing by the spark plug 2. The reference conditions include, for example, the in-cylinder pressure (for example, 4 MPa or more) of the engine 5 at the ignition timing by the spark plug 2, the size G (for example, 0.9 mm or more) of the discharge gap 20, and the screw diameter of the spark plug 2 (for example, M12 or less). ), The net average effective pressure of the engine 5 (for example, a predetermined threshold value or more), and the like. Further, the reference condition may be a combination of these conditions.

(Example 2)
This example is an example of investigating conditions in which it is difficult to normally generate arc discharge in the discharge gap of the spark plug.
FIG. 8 shows the relationship between the crank angle (deg) of the engine and the in-cylinder pressure (MPa). The in-cylinder pressure is a value during motoring of an engine with a compression ratio of 10. The solid line X1 is an example in which the engine intake pressure is 0.12 MPa, and the dotted line X2 is an example in which the engine intake pressure is 0.10 MPa. The screw diameter of the spark plug is M14. The size of the discharge gap is 0.9 mm.

Next, under each condition shown in FIG. 8, an arc discharge was generated in the spark plug, and it was observed whether the arc discharge was normally generated in the discharge gap. The engine was a visualization engine provided with an observation window so that the combustion chamber could be observed with a camera.
In an example in which the engine intake pressure is 0.12 MPa (solid line X1 in FIG. 8), the engine crank angle is in a region C of −10 to 10 degrees, and the in-cylinder pressure of the engine is 4 MPa or more (the engine crank angle is −10 to 10). In the case of 10 deg area Y), there was a case where the arc discharge could not be normally generated in the discharge gap of the spark plug. On the other hand, in the example where the intake pressure of the engine is 0.1 MPa (solid line X2 in FIG. 8), arc discharge can be normally generated in the discharge gap regardless of the in-cylinder pressure of the engine.

  From the above results, under the condition that the engine intake pressure is 0.1 MPa or more and the engine in-cylinder pressure is 4 MPa or more, the streamer discharge is performed immediately before the arc discharge, so that the arc is normally generated in the discharge gap of the spark plug. It becomes possible to generate discharge. That is, even under conditions where it is difficult to normally generate arc discharge in the discharge gap of the spark plug, it is possible to normally generate arc discharge in the discharge gap.

(Example 3)
In this example, the performance of the ignition device is evaluated.
In this example, the ignition device of Example 1 (Example E) and the ignition device as a comparative example (Comparative Example C) were prepared. The ignition device of Example E is configured to perform streamer discharge immediately before arc discharge at the spark plug. That is, the arc discharge is performed immediately after the streamer discharge. Further, the ignition device of Comparative Example C is configured to perform only arc discharge with an ignition plug.

  For each of the ignition devices of Example E and Comparative Example C, spark plugs having a screw diameter equivalent to M12 and M14 were prepared. The thing equivalent to M12 means that the screw diameter of the mounting screw portion of the housing in the spark plug is M14, but the inner diameter of the housing, the insulator on the inside thereof, etc. are equivalent to M12. Specially manufactured for mounting on the engine cylinder head. Moreover, the size of the discharge gap of the spark plug was set to 1.1 mm.

  Next, in the ignition device of Example E, after performing streamer discharge with an ignition plug, arc discharge is performed. Further, in the ignition device of Comparative Example C, only arc discharge is performed with the spark plug. Then, the state of the arc discharge is photographed with a high-speed camera, and it is confirmed whether or not the arc discharge is normally generated in the discharge gap. This operation is performed 100 times to determine the fire rate. Here, the flying ratio refers to the ratio of the number of times arc discharge has normally occurred in the discharge gap to the number of arc discharges. The spark ratio is a spark ratio at the ignition timing TDC (top dead center) by the spark plug.

FIG. 9 shows the spark ratio (%) in the ignition devices of Example E and Comparative Example C.
As shown in the figure, the ignition device of Example E has a high spark rate compared to the ignition device of Comparative Example C in which only arc discharge is performed by performing streamer discharge immediately before arc discharge. In particular, when the screw diameter of the spark plug is equivalent to M12, the spark rate of the ignition device of Comparative Example C is very low even though the spark rate of the ignition device of Example E is equivalent to M12. Was 100%.

  From the above results, it has been found that it is very effective to perform streamer discharge immediately before arc discharge in order to normally generate arc discharge in the discharge gap of the spark plug. In particular, when the screw diameter of the spark plug is M12 or less, which is a condition in which it is difficult to normally generate an arc discharge in the discharge gap of the spark plug, the streamer discharge is performed immediately before the arc discharge, so that the discharge gap is normal. It was found that arc discharge can be generated.

In this example, the experiment was performed by changing the screw diameter of the spark plug. However, the same result can be obtained when the same experiment is performed by changing the size of the discharge gap.
Specifically, when the size of the discharge gap is 0.9 mm or more, which is a condition in which it is difficult to normally generate arc discharge in the discharge gap of the spark plug, streamer discharge is performed immediately before the arc discharge. It becomes possible to generate arc discharge normally in the discharge gap.

Example 4
In this example, the reference condition in the ignition device is changed.
The reference condition in the ignition device of this example is that the net mean effective pressure (BMEP: Brake Mean Effective Pressure; hereinafter simply referred to as BMEP) of the engine is equal to or higher than a predetermined threshold value P2. 05 MPa.

That is, the ignition device is configured to generate the streamer discharge immediately before the arc discharge is generated in the spark plug under the condition where the engine BMEP is equal to or greater than the threshold value P2. That is, arc discharge is performed after performing streamer discharge.
Other basic configurations of the ignition device are the same as those of the first embodiment (see FIGS. 1 and 2).

The engine BMEP threshold value P2 was set according to the following procedure.
First, at each value of the engine BMEP, only arc discharge was performed 100 times on the spark plug, and the relationship between the engine BMEP and the spark ratio was examined. And the value of BMEP of the engine in which the flying ratio changes from 100% to less than 100% was set as the threshold value P2. In this example, the threshold P2 of the engine BMEP was set to 1.05 MPa.

FIG. 10 shows the relationship between the engine speed (× 100 times / min) and BMEP (MPa).
In this example, the threshold value P2 of the engine BMEP, which is the reference condition, is set to 1.05 MPa. Therefore, in the region B in the figure where the engine BMEP is 1.05 MPa or more, immediately before the arc discharge at the spark plug. Perform streamer discharge. That is, arc discharge is performed after performing streamer discharge.

In the case of this example, the arc discharge and the streamer discharge in the ignition device can be easily controlled by previously setting the reference condition in the ignition device based on the value of the BMEP of the engine.
Other basic functions and effects are the same as those of the first embodiment.

(Example 5)
In this example, the optimum condition of the time T from the start of the application of the streamer discharge voltage to the discharge gap of the spark plug until the start of the application of the arc discharge voltage is examined.
In this example, first, as shown in FIG. 11, the tip of the center electrode 21 of the spark plug 2 is opposed to the ground 240. At this time, the distance between the tip of the center electrode 21 and the ground 240, that is, the size G of the discharge gap 20 is set to 5 mm. In this example, since the experiment is performed at atmospheric pressure, the size G of the discharge gap 20 is a very large value of 5 mm. Further, the size G of the discharge gap 20 of 5 mm is a condition in which it is difficult to normally generate an arc discharge in the discharge gap 20 of the spark plug 2 at atmospheric pressure.

  Next, streamer discharge is generated immediately before the spark plug 2 generates arc discharge. That is, arc discharge is performed after performing streamer discharge. Then, the state of the arc discharge is photographed with a high-speed camera, and it is confirmed whether or not the arc discharge is normally generated in the discharge gap 20. This operation is performed 100 times at each time T, and the relationship between the time T and the fire rate is obtained.

FIG. 12 shows the relationship between the time T (μ seconds) and the firing rate (%).
As shown in the figure, when the time T is 120 μsec or less, the spark rate is high, and when the time T is 60 μsec or less, the spark rate is 100%. That is, the shorter the time T, the higher the probability that arc discharge will normally occur in the discharge gap of the spark plug.
From the above results, it is desirable that the time T is 120 μsec or less. The time T is more preferably 60 μsec or less.

DESCRIPTION OF SYMBOLS 1 Ignition device 2 Spark plug 20 Discharge gap 31 Power source for arc discharge 32 Power source for streamer discharge 41 Arc discharge control means 42 Streamer discharge control means 5 Engine (internal combustion engine)

Claims (10)

A spark plug (2) disposed in the internal combustion engine (5) and having a discharge gap (20);
An arc discharge power source (31) for applying an arc discharge voltage to the discharge gap (20) of the spark plug (2);
Arc discharge control means (4, 41) for controlling the timing at which arc discharge is generated by applying the arc discharge voltage from the arc discharge power source (31) to the discharge gap (20) of the spark plug (2). When,
A streamer discharge power source (32) for applying a streamer discharge voltage to the discharge gap (20) of the spark plug (2);
Streamer discharge control means (4, 42) for controlling when the streamer discharge is generated by applying the streamer discharge voltage from the streamer discharge power source (32) to the discharge gap (20) of the spark plug (2). And
Under reference conditions in which arc discharge cannot be generated in the discharge gap (20) simply by applying the arc discharge voltage to the discharge gap (20) of the spark plug (2), the arc discharge control means ( 4, 41) immediately before the arc discharge is generated by applying the arc discharge voltage to the discharge gap (20) of the spark plug (2) by the streamer discharge control means (4, 42). An ignition device for an internal combustion engine (1), wherein the streamer discharge is generated by applying the streamer discharge voltage to the discharge gap (20) of (2).   The ignition device (1) according to claim 1, wherein the reference condition includes that the intake pressure of the internal combustion engine (5) is 0.1 MPa or more at an ignition timing by the ignition plug (2). An ignition device (1) for an internal combustion engine.   The ignition device (1) according to claim 1 or 2, wherein the reference condition includes that an in-cylinder pressure of the internal combustion engine (5) is 4 MPa or more at an ignition timing by the ignition plug (2). An ignition device (1) for an internal combustion engine.   The ignition device (1) according to any one of claims 1 to 3, wherein the reference condition is that the size of the discharge gap (20) of the spark plug (2) is 0.9 mm or more. An ignition device for an internal combustion engine (1), characterized in that   The ignition device (1) according to any one of claims 1 to 4, wherein the spark plug (2) includes a center electrode (21) and an insulator (22) that holds the center electrode (21) inside. ), A housing (23) that holds the insulator (22) on the inside and has a mounting screw portion (231) screwed into the internal combustion engine (5) on the outer peripheral surface, and the center electrode ( 21) and a ground electrode (24) that forms the discharge gap (20), and the reference condition includes that the screw diameter of the mounting screw portion (231) is M12 or less. An ignition device (1) for an internal combustion engine.   The ignition device (1) according to any one of claims 1 to 5, wherein the reference condition includes that the net average effective pressure of the internal combustion engine (5) is a predetermined threshold value or more. Ignition device (1) for an internal combustion engine characterized by the above.   The ignition device (1) according to any one of claims 1 to 6, wherein the streamer discharge voltage is applied to the discharge gap (20) of the spark plug (2) by the streamer discharge control means (4, 42). The time T from the start of application of arc to the start of application of the arc discharge voltage to the discharge gap (20) of the spark plug (2) by the arc discharge control means (4, 41) is 120 μsec. An ignition device (1) for an internal combustion engine, characterized in that:   The ignition device (1) for an internal combustion engine according to claim 7, wherein the time T is 60 µsec or less.   The ignition device (1) according to any one of claims 1 to 8, wherein the streamer discharge voltage applied to the discharge gap (20) of the spark plug (2) from the streamer discharge power source (32). Is an ignition device (1) for an internal combustion engine, characterized in that the voltage waveform has a half-value width of 100 nsec or less.   The ignition device (1) according to any one of claims 1 to 9, wherein the discharge gap of the spark plug (2) is controlled by the arc discharge control means (4, 41) under a condition other than the reference condition. Immediately before the arc discharge voltage is generated by applying the arc discharge voltage to (20), the streamer discharge control means (4, 42) causes the streamer discharge for the discharge gap (20) of the spark plug (2). An ignition device (1) for an internal combustion engine, which is configured not to generate a streamer discharge by applying a voltage.

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