JP2010218768A - Plasma type ignition plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve lifetime of a plasma type ignition plug. <P>SOLUTION: In the ignition plug 10 having a central electrode 11, an insulator 12, a ground electrode 13 for surrounding an outer side face 12c and a tip surface 12a of the insulator 12 and having an opening 131 at a tip side, and a chamber 14 which opens on the opening 131 located at a tip of the ground electrode 13, a projection section 135 axially projecting at a base end side of the central electrode 11 is arranged on the tip of the ground electrode 13. Thus, a discharge gap 15 becomes equal to that of a conventional ignition plug since the projection section 135 of the ground electrode 13 is melted away on the basis of long-term use of the ignition plug 10, but the ignition plug 10 has lifetime and a consumption-resistant nature equal to the conventional ignition plug from this point. Namely, the lifetime of the ignition plug 10 improves only for a period up to melting-away of the projection section 135. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a plasma ignition plug for an internal combustion engine that ejects into a hot gas combustion chamber and ignites an air-fuel mixture.

  In addition to a spark plug that ignites an air-fuel mixture by spark discharge, a plasma-type ignition plug that is disclosed in Patent Document 1 and generates a high-temperature gas to ignite the air-fuel mixture is known.

  Specifically, a plasma spark plug includes a center electrode, an insulator that holds the center electrode, a ground electrode that holds the insulator, and a discharge space (hereinafter referred to as a chamber) surrounded by the tip surface of the center electrode and the insulator. Provided). The chamber includes an opening that opens toward the combustion chamber, and high-temperature gas generated by spark discharge and plasma discharge between the center electrode and the ground electrode is ejected from the opening to ignite the mixture. Here, the high-temperature gas refers to a gas containing a plasma gas exhibiting electrical neutrality at a high temperature of several thousand degrees C. or higher and ionized into positive ions and electrons.

  In such a plasma ignition plug, a high-temperature region having a larger volume than that of a spark plug is generated, and high-temperature gas is generated in a chamber in a substantially closed space. Since flame nuclei (plasma) are formed almost without being affected by the above, it is suitable for a lean burn engine or the like. In addition, since flame nuclei are generated in the chamber, flame nuclei are less likely to be blown out by the air flow generated in the combustion chamber compared to a spark plug that discharges in the combustion chamber, and the mixture is stably mixed even during supercharging. Can ignite.

JP 2006-294257 A

  However, as shown in FIG. 7, in the plasma type spark plug, a high energy of, for example, 100 mJ is applied to the spark plug every time the air-fuel mixture is ignited, so that the heat generated in the chamber causes the center electrode 511 or Electrode consumption due to melting damage such as melting, scattering and sputtering of the ground electrode 513 is severe. When the wear progresses in this way, the distance between the center electrode 511 and the ground electrode 513 increases, so that not only the ignitability of the spark plug 50 decreases, but also discharge for spark discharge to stabilize the ignitability. When the voltage is increased, the life of the spark plug 50 is reduced.

  Therefore, in view of such circumstances, the present invention aims to improve the life of a plasma spark plug.

  In order to achieve the above object, a plasma ignition plug of the invention according to claim 1 surrounds a center electrode, a cylindrical insulator holding the center electrode from the outside, an outer side surface and a tip surface of the insulator, A chamber that is surrounded by a ground electrode having an opening on the tip side, a tip surface of the center electrode, an inner side surface of the insulator, and an inner side surface of the ground electrode connected to the inner side surface of the insulator; In the plasma ignition plug having the above-described configuration, a protruding portion that protrudes toward the axially proximal end of the center electrode is provided at the tip of the ground electrode.

  In other words, since the distance between the center electrode and the ground electrode where the discharge is performed is shortened by the protruding portion, even if the center electrode or the ground electrode is melted away by using the plasma spark plug, the component is not present Thus, the life of the plasma spark plug can be improved as compared with the prior art by the period during which the protruding portion melts.

  According to a second aspect of the present invention, the inner side surface of the insulator and the inner side surface of the protrusion are provided on the same plane. Thereby, since the spark discharge is likely to generate creeping discharge along the inner side surface of the insulator, the required discharge voltage is reduced, and the insulator can be prevented from being melted.

  According to invention of Claim 3, the closed space enclosed by the front end surface of an insulator, the inner surface of a ground electrode, and the outer side surface of a protrusion part is formed. The closed space is formed when the plasma spark plug is manufactured, and is formed of an air layer. The closed space has a lower thermal conductivity than the ground electrode or the like, and becomes a lower temperature than the ground electrode when the plasma spark plug is used. Therefore, the temperature rise of the ground electrode that is directly affected by the Joule heat generated in the chamber can be suppressed by the closed space having a relatively low temperature. Thereby, the melting loss of a ground electrode is suppressed and the lifetime of a plasma-type spark plug can be improved.

  According to a fourth aspect of the present invention, the distance between the center electrode and the protruding portion is 1.0 mm or more and 2.0 mm or less. That is, by optimizing the distance between the center electrode where the spark discharge occurs and the protrusion, the discharge voltage required for the spark discharge can be reduced without impairing the ignitability of the plasma ignition plug. Thereby, the progress of the melting loss of the center electrode or the ground electrode can be delayed, and the life of the plasma spark plug can be improved.

1 is a circuit diagram of a plasma ignition device according to an embodiment of the present invention. It is the whole figure and partial sectional view of a spark plug concerning an embodiment of the present invention. It is the A section enlarged view in FIG. It is a schematic diagram which shows consumption of a spark plug. It is a schematic diagram which shows the modification of FIG. It is a schematic diagram which shows the modification of FIG. It is a schematic diagram which shows consumption of the conventional spark plug.

  Embodiments of a plasma ignition plug embodying the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a plasma ignition device for generating a high-temperature gas in a plasma ignition plug (hereinafter referred to as an ignition plug 10) according to the present invention.

  A plasma ignition device 100 shown in FIG. 1 is mounted on an engine of, for example, a four-cycle, four-cylinder vehicle, generates a hot gas (not shown), and ignites an air-fuel mixture, and a battery. An ignition control circuit 20 connected to supply ignition energy for generating high temperature gas to the spark plug 10, and connected to the ignition control circuit 20, an ignition timing of the ignition plug 10 and a fuel injection timing of an injector (not shown). And an electronic control unit 30 for controlling the above. In the present embodiment, the spark plug 10 and the ignition control circuit 20 are provided for each cylinder of the engine, and one electronic control device 30 is provided for one engine.

  Here, the spark plug 10 will be described with reference to FIG. FIG. 2 is a front view in which a main part of the spark plug 10 is broken. The spark plug 10 includes a center electrode 11, a center shaft 111 that connects the center electrode 11 and an ignition coil (not shown), and the center electrode 11 and the center shaft 111. , The ground electrode 13 surrounding the tip surface 12a and the outer side surface 12c of the insulator 12, the tip surface 11a of the center electrode 11, the inner side surface 12b of the insulator 12, and the inner side of the insulator 12. The chamber 14 is an open space surrounded by the inner side surface 13b of the ground electrode 13 connected to the side surface 12b. In the chamber 14, a path in which a spark discharge described later occurs between the center electrode 11 and the ground electrode 13 is defined as a discharge gap 15.

  In addition, the spark plug 10 holds the center electrode 11 in the shaft hole of the insulator 12, inserts the insulator 12 inside the ground electrode 13, and then crimps the insulator 12 and the ground electrode 13. Are manufactured by fixing them together.

  As shown in FIG. 1, the ignition control circuit unit 20 connected to the spark plug 10 is composed of, for example, a CDI type power supply circuit, and generates a spark discharge in the discharge gap 15 between the center electrode 11 and the ground electrode 13. A spark discharge circuit unit 21 for generating the gas, and a plasma discharge circuit unit 22 for generating a high-temperature gas in the chamber 14 using the spark discharge as a trigger. In the present embodiment, the center electrode 11 is a negative electrode and the ground electrode 13 is a positive electrode.

  The spark discharge circuit unit 21 is electrically connected to the center electrode middle shaft 111 of the spark plug 10 and controlled by the electronic control device 30, and applies a discharge voltage of, for example, 15 to 25 kV to the discharge gap 15 to discharge the spark plug 10. This is a power supply circuit unit that generates a spark discharge by causing dielectric breakdown of the gap 15.

  Specifically, the spark discharge circuit unit 21 includes a primary coil 211 and a primary circuit connected to the primary coil 211, and a secondary coil 212 and a secondary circuit connected to the secondary coil 212. A secondary current generated in the secondary coil 212 is supplied to the spark plug 10 to generate a spark discharge in the discharge gap 15. Here, the spark discharge in the present embodiment is a creeping discharge that discharges on the inner side surface 12 b of the insulator 12 from the center electrode 11 toward the ground electrode 13, and in the air from the center electrode 11 toward the ground electrode 13. It refers to both or either of the air discharges that are discharged.

  The primary coil 211 is formed, for example, by winding an enameled wire having a diameter of 0.3 mm to 0.8 mm for 100 to 222 turns. On the other hand, the secondary coil 212 is formed, for example, by winding an enamel wire having a diameter of 30 μm to 50 μm for 10,000 to 21,000 turns. The primary coil 211 is energized with a primary current based on an ignition pulse signal transmitted from the electronic control unit 30 described later. A secondary current is generated in the secondary coil 212 by a mutual induction effect caused by a change in magnetic flux when the primary current is passed through the primary coil 211, and a discharge voltage of 10 to 40 kV is applied to the spark plug 10.

  A primary side circuit for supplying a primary current to the primary coil 211 includes a spark discharge capacitor 213, a spark discharge power source 214, a thyristor 215, a diode 216, and the like.

  The spark discharge capacitor 213 has, for example, an electric capacity of 1 to 3 μF, and is connected to a spark discharge power source 24 including a DC-DC converter connected to a battery mounted on the vehicle. It is charged to a voltage, for example 210-300V.

  A thyristor 215, which is a switching element, is provided between the spark discharge power source 214 and the positive electrode (left electrode in FIG. 1) of the spark discharge capacitor 213 in the forward direction with respect to the ground. It is turned on based on the ignition pulse signal transmitted from the electronic control unit 30. When the thyristor 215 is turned on, the spark discharge capacitor 213 in which a predetermined amount of electricity is stored is discharged through the thyristor 215, and a primary current is passed through the primary coil 211. A diode 216 connected to the negative electrode of the spark discharge capacitor 213 rectifies the primary current and generates a desired secondary voltage in the secondary coil 212 described later.

  Next, a secondary circuit that supplies a secondary current to the secondary coil 212 includes a diode 217, an electric resistor 218, and the like. The secondary current generated in the secondary coil 212 due to the mutual induction action between the primary coil 211 and the secondary coil 212 is energized to the spark plug 10 via the diode 217 and the electric resistance 218. The diode 217 prevents the plasma current from flowing from the plasma discharge circuit unit 22 described later to the secondary coil 212 side, while the electric resistance 218 provided on the downstream side of the diode 217 prevents the plasma discharge circuit unit 22 described later. Removes noise caused by the flowing current.

  The plasma discharge circuit unit 22 is electrically connected to the center electrode 11 of the spark plug 10 and is controlled by the electronic control device 30 to generate high energy in the discharge gap 15 with the occurrence of spark discharge in the discharge gap 15 as a trigger. It is a power supply circuit unit for supplying and generating high temperature gas in the chamber 14. Note that one plasma discharge circuit unit 22 may be provided for each of a plurality of cylinders of the engine, for example, for two spark discharge circuit units 21.

  Specifically, the plasma discharge circuit unit 22 includes a plasma discharge capacitor 221, a plasma discharge power source 222, two diodes 223 and 224, etc., and supplies a plasma current to the spark plug 10, and a high temperature gas to the chamber 14. Is generated.

  The plasma discharge capacitor 221 has an electric capacity of 0.2 to 4 μF, for example, and is supplied with a predetermined voltage, for example, 400 to 900 V by a plasma discharge power source 222 composed of a DC-DC converter or the like connected to the battery. Is applied. The charging of the plasma discharge capacitor 221 is terminated by turning off the plasma discharge power supply 222 at the start of energization of the primary current (when the ignition pulse signal is transmitted to the thyristor 215), for example. Thereafter, the voltage of the discharge gap 15 drops due to the spark discharge generated in the spark plug 10 and falls below the voltage of the plasma discharge capacitor 31. Simultaneously, a plasma current of 150 A, 100 mJ, for example, flows from the plasma discharge capacitor 221 to the spark plug 10. Energized. The two diodes 223 and 224 prevent the secondary voltage of the spark discharge circuit unit 21 from being applied to the plasma discharge capacitor 221 and the plasma discharge power supply 222 to be destroyed.

  The electronic control unit 30 is mainly composed of a microcomputer composed of a CPU, ROM, RAM, etc. (not shown), and executes various control programs stored in the ROM, so that ignition control is performed according to each engine operating condition. Etc. Specifically, as the ignition control, the electronic control unit 30 determines an ignition timing (based on various detection signals input from a crank angle sensor, an intake pipe pressure sensor, and the like, which are attached near the crankshaft of an unillustrated engine, as needed. Ignition timing, fuel injection timing) is calculated, an ignition pulse signal is output to the thyristor 215 based on the calculation result, and a fuel injection pulse signal is output to an injector drive circuit (not shown).

  Further, the electronic control unit 30 charges the plasma discharge capacitor 31 by driving and controlling the plasma discharge power supply 222. Specifically, the electronic control unit 30 turns on the plasma discharge power source 222 when the predetermined standby time has elapsed from the ignition timing and plasma discharge is completed, starts charging the plasma discharge capacitor 221, and performs the next ignition. The charging of the plasma discharge capacitor 221 is stopped by turning off the plasma discharge power supply 222 at a certain time before the timing, for example, at the start of energization of the primary coil 211. In other words, the plasma discharge capacitor 221 repeatedly performs charging between ignition timings and discharging at the ignition timing.

  Hereinafter, the spark plug 10 of the present invention will be described in detail with reference to FIGS. 2 and 3. 2 and 3, the upper side of the spark plug 10 is described as the base end side, the lower side as the front end side, the radially outer side as the outer side, and the radial inner side as the inner side.

  As described with reference to FIG. 2, the spark plug 10 of the present invention includes a columnar center electrode 11 made of a conductive metal material, a substantially cylindrical insulator 12 that insulates and holds the center electrode 11, and an insulator 12. And a ground electrode 13 made of a substantially cylindrical metal.

  The front end side of the center electrode 11 is formed in a long axis shape by a conductive material such as iridium or an iridium alloy, for example, and the center electrode center shaft made of a metal material having good electrical conductivity and high thermal conductivity such as a steel material or copper inside. 111 is formed, and the base end side is exposed from the insulator 12 and is electrically connected to the spark discharge circuit unit 21 and the plasma discharge circuit unit 22.

  The insulator 12 is made of a material having excellent heat resistance such as high-purity alumina, mechanical strength, dielectric strength at high temperature, thermal conductivity, and the like, and the tip side is electrically insulated from the center electrode 11 and the ground electrode 13. The base end side ensures electrical insulation between the center electrode middle shaft 111 and a housing part 133 to be described later.

  The ground electrode 13 is formed with an opening 131 that is a round hole that opens toward the combustion chamber (not shown) at the center on the tip side. On the other hand, on the base end side, there are a housing part 133 for storing and holding the insulator 12, and a hexagonal part 134 for screwing a screw part 132 screwed to the engine on the outside of the housing part 133. It is arranged on the end side. The housing portion 133 including the ground electrode 13 is formed of a metal material such as nickel or iron, and the housing portion 133 is grounded to the engine.

  FIG. 3 is an enlarged view of part A in FIG. As shown in FIG. 3, on the inner side of the insulator 12, the front end surface 11a of the center electrode 11, the inner side surface 12b of the insulator 12, and the inner side surface 13b of the ground electrode 13 connected to the inner side surface 12b of the insulator 12 A chamber 14 that is an open space surrounded by is formed. The opening 131 of the ground electrode 13 is located at the tip of the chamber 14, and the high temperature gas generated in the chamber 14 is ejected from the opening 131 toward the combustion chamber.

  Here, the characteristic part of the spark plug 100 of this invention is demonstrated below.

  An annular projecting portion 135 projecting toward the proximal end side in the axial direction of the central core 11 is provided inside the proximal end surface 13 c in the vicinity of the opening 131 of the ground electrode 13. Further, a part of the insulator 12 where the distal end surface 12a and the inner side surface 12b cross each other is provided with an engaging portion 121 that is partially recessed toward the base end side and the outer side. Engage. The protrusion 135 is connected to the ground electrode 13, and the inner side surface 135 b of the protrusion 135 is connected to the inner side surface 12 b of the insulator 12. Due to the projecting portion 135 projecting from the distal end of the ground electrode 13 toward the proximal end side, the discharge gap 15 between the center electrode 11 and the ground electrode 13 is shortened as compared with the conventional spark plug without the projecting portion 135. As shown in FIG. 4, the long-term use of the spark plug 10 causes the protruding portion 135 of the ground electrode 13 to melt, resulting in a discharge gap 15 equivalent to the conventional one. However, the spark plug 10 is equivalent to the conventional one from this point. Has life and wear resistance. That is, the life of the spark plug 10 is improved as compared with the conventional case by the period until the protrusion 135 is melted.

  In addition, since the discharge gap 15 is shorter than before in the period until the protrusion 135 melts down, the discharge voltage when the spark discharge circuit portion 21 generates a spark discharge is reduced to, for example, 10 kV, and the center electrode 11 or The consumption of the ground electrode 13 can be suppressed. At this time, the discharge gap 15 from the proximal end surface 135a of the protrusion 135 to the distal end surface 11a of the center electrode 11 is 1.0 to 2.0 mm, and more preferably 1.5 mm. When the discharge gap 15 is less than 1.0 mm, when the fuel, engine oil, water droplets, etc. enter the chamber 14 during engine operation, the insulation resistance between the center electrode 11 and the ground electrode 13 is lowered, causing leakage. This is unsuitable because there is a high possibility that the spark discharge will not occur, and if the discharge gap 15 is larger than 2.0 mm, the effect of reducing the discharge voltage of the spark discharge can be obtained. Since it is not, it is not preferable. That is, by reducing the discharge voltage and defining a suitable discharge gap 15, it is possible to improve the life of the spark plug 10 while ensuring the ignitability of the spark plug 10.

Further, in the spark plug 10 according to the present embodiment, when the insulator 12 is inserted and fixed in the ground electrode 13 in the manufacturing process, the projecting portion 135 and the engaging portion 121 are engaged at the same time, and the tip of the insulator 12 is also engaged. An annular closed space 16, which is an air layer, is formed between the surface 12 a, the base end side end surface 13 c of the ground electrode 13, and the outer side surface 135 c of the protruding portion 135. The closed space 16 made of an air layer has a lower thermal conductivity than the ground electrode 13 made of metal or the like, and has a lower temperature than the ground electrode 13 when the spark plug 10 is used. Due to the closed space 16 having a relatively low temperature, an increase in the temperature of the ground electrode 13 that is directly affected by Joule heat in the chamber 14 and becomes a high temperature can be reduced. Thereby, the melting loss of the ground electrode 13 can be suppressed and the life of the spark plug 10 can be improved. In the present embodiment, the volume of the closed space 16 is set to 2.6 mm ^3, the desired ignition performance can be obtained as long as it is within the range of 2.0mm ³ ~3.5mm 3.

  In addition, when the spark plug 10 is manufactured, when the insulator 12 is inserted inside the ground electrode 13, the engagement portion 121 provided on the insulator 12 side and the protrusion 135 provided on the ground electrode 13 side are engaged. By combining, the insulator 12 can be positioned with respect to the ground electrode 13.

  Further, since the inner side surface 12b of the insulator 12 and the inner side surface 135b of the ground electrode 13 and the protrusion 135 are connected on the same plane, the spark discharge between the electrodes 11 and 13 is caused by the inner side surface 12b of the insulator 12. Therefore, the required discharge voltage is reduced, and the insulator 12 can be prevented from being melted.

Furthermore, the energy of the high-temperature gas generated in the chamber 14 does not leak into the closed space 16 by spatially separating the chamber and the closed space 16 by the protruding portion 135 and the engaging portion 121. Since the reduction of the energy of the high temperature gas is also suppressed, the ignitability of the spark plug 10 can be further improved.
(Other embodiments)
In the above embodiment, the protruding portion 135 is formed integrally with the ground electrode 13. However, as shown in FIG. 5, the protruding portion 235 is formed separately from the ground electrode 13, and the protruding portion 235 is connected to the ground electrode 13. You may join by laser welding etc. In this case, it is possible to further improve the life of the spark plug 10 by forming the protruding portion 235 where creeping discharge is generated from a rare metal such as iridium or rhodium having a high melting point and joining the protruding portion 235 to the ground electrode 13. Moreover, as shown in FIG. 5, even if it makes the protrusion part 235 and the engaging part 221 each taper-shape, it can have an effect similar to the above.

  In the above embodiment, the inner side surface 12b of the insulator 12 and the inner side surface 135b of the protrusion 135 are connected on the same plane, but the inner side surface 135b of the protrusion 135 is the inner side surface of the insulator 12. The inner side surface 12b of the insulator 12 and the inner side surface 135b of the projecting portion 135 may be connected to each other via a part of the proximal end surface 135a of the projecting portion 135.

  Further, in the above-described embodiment, the necessary charge accumulated in the spark discharge capacitor 213 is discharged to the primary coil 211 at once, a sudden magnetic flux change is given to the ignition coil 10, and a high voltage is generated in the secondary coil 212. However, a switching element (not shown) such as a MOS-FET is provided in the primary side circuit of the spark discharge circuit unit 21, and an induced electromotive force is generated in the secondary coil 212 by turning on and off the switching element. A full transistor system in which a high voltage is applied to the spark plug 10 may be employed.

10 ... Spark plug (plasma spark plug),
11 ... center electrode,
111 ... center electrode central axis,
11a ... tip surface,
12 ... Insulator,
121... Engaging portion,
12a ... tip surface,
12b ... inner side surface,
12c ... outer side surface,
13: Ground electrode,
13b ... the inner side,
13c ... the end face on the base end side,
131 ... opening,
132 ... screw part,
133 ... housing part,
134 ... hexagonal part,
135, 235 ... projecting portion,
135a: proximal end surface,
135b ... inner side surface,
135c ... outer side surface,
14 ... Chamber,
15 ... discharge gap,
16 ... closed space,
20 ... Ignition control circuit,
21 ... Spark discharge circuit part,
211 ... primary coil,
212 ... secondary coil,
213 ... Spark discharge capacitor,
214 ... Spark discharge power source 215 ... Thyristor,
216, 217 ... diode,
218 ... electric resistance,
22: Plasma discharge circuit section,
221: Plasma discharge capacitor,
222: Power source for plasma discharge,
223, 224 ... diodes,
30 ... Electronic control unit,
100: Plasma ignition device

Claims (4)

A center electrode;
A cylindrical insulator for holding the center electrode from the outside;
A ground electrode surrounding the outer side surface and the front end surface of the insulator and having an opening on the front end side;
A plasma ignition comprising a chamber surrounded by the tip surface of the center electrode, an inner side surface of the insulator, and an inner side surface of the ground electrode connected to the inner side surface of the insulator and opening at the opening. In the plug,
The plasma ignition plug according to claim 1, wherein a protrusion projecting toward a base end side in the axial direction of the center electrode is provided at a tip of the ground electrode.   The plasma ignition plug according to claim 1, wherein an inner side surface of the insulator and an inner side surface of the protrusion are provided on the same plane.   3. The plasma ignition plug according to claim 1, wherein a closed space surrounded by a tip surface of the insulator, an inner surface of the ground electrode, and an outer side surface of the projecting portion is formed.   The plasma ignition plug according to any one of claims 1 to 3, wherein a distance between the center electrode and the protrusion is 1.0 mm or more and 2.0 mm or less.

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