JP5618754B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug for a spark ignition type internal combustion engine, and more particularly, to an ignition plug that implements an ignition method in which an induced voltage generated by an ignition coil and a high-frequency electric field generated by an electric field generating circuit are superimposed and applied to an electrode of the spark plug. Regarding spark plugs.

  In an ignition device mounted on a spark ignition type internal combustion engine, a high voltage generated in the ignition coil when the igniter is extinguished is applied to the center electrode of the ignition plug, so that the center electrode of the ignition plug and the ground electrode are A spark discharge is caused between and ignited.

  Recently, in order to ensure that the air-fuel mixture in the combustion chamber is ignited and a stable flame can be obtained, an electric field generation circuit, in other words, a high frequency voltage output from a high frequency oscillator is applied to the central electrode. An “active ignition” method has been attempted in which spark ignition is performed using an induction voltage generated by an ignition coil (see, for example, the following patent document). According to the active ignition method, a high-frequency electric field is formed in the space between the center electrode and the ground electrode. Then, the plasma generated in the high-frequency electric field grows, and a large flame nucleus that starts the flame propagation combustion can be generated.

  However, plasma is susceptible to gas flow in the combustion chamber. Therefore, it is possible that the bent plasma is blown off and cannot remain in the vicinity of the spark plug, and the expected combustion acceleration effect by volume ignition cannot be obtained.

Japanese Patent Application No. 2009-255843

  An object of the present invention is to make it possible to generate a large plasma flame nucleus even under the influence of an air flow in a combustion chamber.

In the present invention, a center electrode that is electrically connected to both the ignition coil that applies a high voltage causing spark discharge and an electric field generation circuit that generates an electric field in the combustion chamber, a first ground electrode that is grounded, A second ground electrode that is grounded and is positioned downstream of the first ground electrode along the gas flow direction in the combustion chamber, and the distance between the second ground electrode and the center electrode is A spark plug larger than the distance between the first ground electrode and the center electrode was formed. In addition, according to the present invention, a spark plug for a spark ignition internal combustion engine is electrically connected to both an ignition coil that applies a high voltage that causes spark discharge and an electric field generation circuit that generates an electric field in the combustion chamber. A center electrode, a grounded first ground electrode, and a grounded second ground electrode positioned downstream of the first ground electrode along a gas flow direction in the combustion chamber. A spark plug that performs arc discharge only with the first ground electrode is configured.

  If the spark plug according to the present invention is used, the plasma blown by the in-cylinder flow is held by the second ground electrode located on the leeward side (collecting ions in the combustion chamber, particularly around the electrode). Can do. And it becomes possible to maintain a plasma between the said 2nd ground electrode and center electrode, and to grow this greatly.

Further, a third ground electrode that is grounded and is positioned upstream of the first ground electrode along the gas flow direction in the combustion chamber may be provided. In that case, it is preferable that a distance between the third ground electrode and the center electrode is larger than a distance between the first ground electrode and the center electrode.

  According to the present invention, an ignition method is implemented in which an induction voltage generated by an ignition coil and a high-frequency electric field generated by an electric field generation circuit are superimposed and applied to an electrode of an ignition plug. Nuclei can be generated.

The block diagram which shows the ignition device and electric field generation circuit in 1st embodiment of this invention. The circuit diagram of the ignition device in the embodiment. The front sectional view of the ignition plug of the embodiment. The sectional side view of the ignition plug of the embodiment. The bottom view of the ignition plug of the embodiment. The figure explaining the specific structure of the electric field generation circuit in the embodiment. The circuit diagram of the H bridge which is an element of the electric field generation circuit in the embodiment. The sectional side view of the ignition plug of 2nd embodiment of this invention. The bottom view of the ignition plug of the embodiment.

  <First Embodiment> An embodiment of the present invention will be described with reference to the drawings. First, the ignition device 1 will be described. The ignition device 1 is used for an internal combustion engine mounted on a vehicle or the like. As shown in FIGS. 1 and 2, the ignition device 1 generates an igniter 11 that receives an ignition signal emitted from the electronic control device 3, and a high induced voltage that causes spark ignition when the igniter 11 receives the ignition signal. The ignition coil 12 to be generated and the spark plug 13 that receives the application of the induced voltage generated in the ignition coil 12 are used as elements.

  The igniter 11 is a semiconductor switching element that is integrally incorporated in a coil case that houses the ignition coil 12.

  The ignition coil 12 is mainly composed of a primary coil and a secondary coil. A plug mounting portion for inserting and mounting the spark plug 13 is provided at the lower end portion of the coil case.

  In the present embodiment, as shown in FIGS. 3 to 5, the spark plug 13 includes a terminal 131 connected to the ignition coil 12 in a state of being inserted into the plug mounting portion of the coil case, and a ground electrode 133. , A conductor 135 connecting the center electrode 132 and the terminal 131, an insulator 136 that covers and insulates the conductor 135, and a housing that supports the insulator 136 from the outside 137 and a plurality of ground electrodes 133 and 134 attached to the lower end of the housing.

  In the illustrated example, the terminal 131, the center electrode 132, and the conductor 135 are integrally formed. However, the terminal 131 and the conductor 135 may be separated from each other and conductively connected to each other, or the center electrode 132 and the conductor 135 may be separated from each other to be conductively connected to each other.

  In known spark plugs, a resistor for reducing noise generated due to spark discharge is often interposed between the center electrode 132 and the terminal 131. Of course, such a resistor may be interposed, but the high-frequency voltage applied to the center electrode 132 from the electric field generating circuit 2 described below may be attenuated by the resistor. Therefore, in this embodiment, instead of providing a resistor between the center electrode 132 and the terminal 131, the noise reduction member 138 is disposed so as to surround the conductor 135. The noise reduction member 138 is a substantially cylindrical member formed using, for example, Ni—Zn ferrite. The imaginary component of the magnetic permeability of the noise reduction member 138 takes a large value in the frequency band to which the generated noise belongs, specifically in the 60 MHz band. The noise reduction member 138 is also covered and insulated by the insulator 136.

  Of the plurality of ground electrodes 133, 134, the main ground electrode 133, which is the first ground electrode, hangs down from the housing 137 over the height of the tip of the center electrode 132, bends inward in the middle, and the center electrode 132 It has a substantially L-shape in front view extending toward the front. The front end portion of the main ground electrode 133 extends to a position immediately below the center electrode 132 and intersects the axis L of the center electrode 132.

  On the other hand, the sub ground electrode 134 as the second ground electrode hangs down from the housing 137 to the vicinity of the height of the tip of the center electrode 132 or in front of it (that is, the height above the tip of the center electrode 132). It stops and forms a substantially L shape in side view that is bent from there and slightly protrudes toward the center electrode 132. The tip of the sub ground electrode 134 is offset outward from the axis L so as not to intersect the axis L of the center electrode 132. A distance D2 between the sub ground electrode 134 and the center electrode 132 is larger than a distance D1 between the main ground electrode 133 and the center electrode 132.

  As shown in FIG. 5, the front end portion of the main ground electrode 133 viewed from the bottom side and the front end portion of the sub ground electrode 134 are separated from each other by about 90 ° along the circumferential direction around the axis L.

  The principle of spark ignition is as follows. When the igniter 11 receives the ignition signal from the electronic control unit 3, the igniter 11 is first ignited and a current flows to the primary side of the ignition coil 12, and the igniter 11 is extinguished at the immediately following ignition timing, and this current is Blocked. Then, a self-induction action occurs, and a high voltage is generated on the primary side. Since the primary side and the secondary side share the magnetic circuit and the magnetic flux, a higher induced voltage is generated on the secondary side. This high induction voltage is applied to the center electrode 132 of the spark plug 13, and a spark discharge is generated between the center electrode 132 and the ground electrode 133.

  Thus, the ignition device 1 is provided with the electric field generation circuit 2, and the high-frequency electric field generated by the electric field generation circuit 2 and the high induction voltage generated by the ignition coil 12 are superimposed and applied to the terminal 131 of the ignition plug 13 and thus to the center electrode 132. Like to do.

  Examples of the electric field generating circuit 2 include an AC voltage generating circuit that applies an AC voltage, and a pulsating voltage generating circuit that applies a pulsating voltage. When the pulsating voltage generation circuit is employed, any circuit may be used as long as it generates a DC voltage whose voltage periodically changes, and its waveform may be arbitrary. The pulsating voltage includes a pulse voltage that varies from a reference voltage (which may be 0V) to a constant voltage in a constant cycle, a voltage obtained by half-wave rectifying an AC voltage, a voltage obtained by adding a DC bias to the AC voltage, and the like. The high-frequency voltage oscillated by the electric field generation circuit 2 preferably has a frequency of about 200 kHz to 1000 kHz and an amplitude of about 3 kVp-p to 10 kVp-p.

  In the present embodiment, the electric field generation circuit 2 is a circuit that converts the low-voltage direct current into high-voltage alternating current using the battery 4 as a power source, as shown in FIGS. 6 and 7. The electric field generation circuit 2 includes a DC-DC converter 21 that boosts a battery 4 voltage of about 12 V to 300 V to 500 V, an H-bridge circuit 22 that converts direct current output from the DC-DC converter 21 into alternating current, and an H-bridge circuit. A step-up transformer 23 that boosts the alternating current output from 22 to a higher voltage is used as an element.

  Further, a first diode 24 and a second diode 25 are provided at the output end of the electric field generating circuit 2. The first diode 24 has a cathode connected to the signal line of the secondary winding of the step-up transformer 23 and an anode connected to the mixer 5, which is a node with the ignition coil 12. The second diode 25 has an anode connected to the ground line of the secondary winding of the step-up transformer 23 and a cathode grounded. The first diode 24 and the second diode 25 play a role of blocking the negative high voltage pulse current flowing from the secondary side of the ignition coil 12 at the ignition timing.

  The high-frequency voltage oscillated by the electric field generating circuit 2 is applied to the center electrode 132 of the spark plug 13 almost simultaneously with the start of the spark discharge, immediately before the start of the spark discharge or immediately after the start of the spark discharge. As a result, a high-frequency electric field is formed in the space between the center electrode 132 and the ground electrodes 133 and 134. Then, a plasma is generated by performing a spark discharge in a high-frequency electric field, and this plasma generates a large radical plasma flame nucleus that starts flame propagation combustion.

  In the above, the flow of electrons due to the spark discharge and the ions and radicals generated by the spark discharge are vibrated and meandered by the influence of the electric field, resulting in a long path length and a dramatic increase in the number of collisions with surrounding water and nitrogen molecules. This is due to the increase. Water molecules and nitrogen molecules that have been struck by ions and radicals become OH radicals and N radicals, and the surrounding gas that has been struck by ions and radicals is also ionized, that is, a plasma state. In addition, the region of ignition of the air-fuel mixture increases and the flame kernel also increases. As a result, the two-dimensional ignition by only the spark discharge is amplified to the three-dimensional ignition, and the combustion rapidly propagates into the combustion chamber and expands at a high combustion speed.

  When using this spark plug 13, as shown in FIG. 5 (a), (b) or (c), in the combustion chamber of the cylinder of the internal combustion engine, the vicinity of the electrodes 132, 133 and 134 of the spark plug is used. The sub ground electrode 134 is positioned downstream of the main ground electrode 133 along the flow direction of the flowing gas (indicated by the white arrow in the figure). The flow of gas in the combustion chamber is determined by the arrangement of the intake and exhaust ports of the cylinder head of the internal combustion engine. When the gas flows from the intake port side toward the exhaust port side in the vicinity of the spark plug electrodes 132, 133, 134, the sub ground electrode 134 is positioned closer to the exhaust port than the main ground electrode 133. In addition, the spark plug 13 is assembled to the cylinder head of the internal combustion engine.

  When ignition is performed by the spark plug 13, a spark discharge is first generated between the center electrode 132 and the main ground electrode 133, and this spark generates plasma under a high-frequency electric field. The generated plasma is caused to flow by the airflow in the combustion chamber. Since the sub-ground electrode 134 exists on the leeward side, the plasma is held between the sub-ground electrode 134 and the center electrode 132, Can be grown greatly.

  When a high frequency electric field having a frequency lower than that of the microwave band is applied in the vicinity of the electrodes 132, 133, and 134 for the purpose of generating a plasma flame nucleus, it takes a long time to generate and grow the plasma, and the generated plasma There is not a small possibility that it will be lost by being blown away. By adopting the spark plug 13, the plasma can be sustained even under conditions where there is a strong in-cylinder flow, and the expected combustion acceleration effect by volume ignition can be obtained.

  Incidentally, since the discharge at the ignition timing is an arc, the main ground electrode 133 is required to have durability. Accordingly, the main ground electrode 133 needs to be coated with a material containing a noble metal such as iridium, platinum, or molybdenum.

  On the other hand, since only the plasma is generated in the vicinity of the sub-ground electrode 134, the damage given to the sub-ground electrode 134 is small in an atmosphere where there are combustion products in the vicinity. Therefore, the durability as high as that of the main ground electrode 133 is not required, and the sub-ground electrode 134 may not be coated with a noble metal material. Also, the tip of the sub ground electrode 134 can be formed into a tapered shape.

  <Second Embodiment> The spark plug 13 of the second embodiment shown in FIGS. 8 and 9 is provided with a plurality of sub-ground electrodes 134. Hereinafter, description will be made with emphasis on the differences from the first embodiment.

  In the present spark plug 13, there are a pair of sub-ground electrodes 134, which are arranged symmetrically about the axis L of the center electrode 132. Each of the sub-ground electrodes 134 has a substantially L-shape in a side view that hangs down from the housing 137 to the vicinity of the height of the tip of the center electrode 132 or in front of it, and then bends and projects slightly toward the center electrode 132. The tip of the sub ground electrode 134 is offset outward from the axis L so as not to intersect the axis L of the center electrode 132. The distance D2 between one sub-ground electrode 134 and the center electrode 132 and the distance D3 between the other sub-ground electrode 134 and the center electrode 132 are both distances between the main ground electrode 133 and the center electrode 132. Greater than D1.

  As shown in FIG. 9, the front end portion of the main ground electrode 133 in bottom view and the front end portion of each sub ground electrode 134 are separated from each other by approximately 90 ° along the circumferential direction around the axis L.

  When the spark plug 13 is used, as shown in FIGS. 9A, 9B, or 9C, in the combustion chamber of the cylinder of the internal combustion engine, the vicinity of the spark plug electrodes 132, 133, and 134 is set. Any sub-ground electrode 134 is positioned downstream of the main ground electrode 133 along the flow direction of the flowing gas (indicated by the white arrow in the figure), and at the same time, the sub-ground electrode 134 on the opposite side is set as the main ground electrode. It is positioned upstream of 133. At this time, with respect to the main ground electrode 133 which is the first ground electrode, the former sub ground electrode 134 is the second ground electrode, and the latter sub ground electrode 134 is the third ground electrode.

  When the present spark plug 13 is employed, the plasma is less likely to be blown than in the first embodiment, and the effect of further stabilizing combustion by volume ignition can be expected. This may be due to the fact that the sub-ground electrode 134 positioned on the windward side of the in-cylinder flow acts as a windbreaker and acts to protect the plasma flame kernel.

  Moreover, the provision of the plurality of sub ground electrodes 134 simplifies the work of assembling the spark plug 13 to the cylinder head. In general, the spark plug 13 is screwed to the cylinder head via a screw formed on the outer periphery of the housing 137. When the number of the sub ground electrode 134 is one as in the spark plug 13 of the first embodiment, the rotation angle at which the sub ground electrode 134 can be positioned on the downstream side of the in-cylinder flow at the time of screwing to the cylinder head is 360 °. Visiting once every time, it is not easy to achieve proper tightening torque. In turn, in the spark plug 13 of the present embodiment, the two sub ground electrodes 134 face each other around the axis L, and the rotation angle at which any of the sub ground electrodes 134 can be positioned downstream of the in-cylinder flow. Visits once every 180 °. For this reason, coexistence with an appropriate tightening torque is easier.

  The present invention is not limited to the embodiment described in detail above. For example, in the above embodiment, the noise reduction member is disposed around the conductor connecting the terminal and the center electrode. Instead, a noise reduction choke coil is provided between the terminal and the center electrode. You may comprise the inserted spark plug. Alternatively, a noise reducing choke coil may be sandwiched between the ignition coil and the spark plug terminal (for example, in the plug mounting portion of the coil case). In this case, it is not necessary to provide a noise reducing member or a choke coil in the spark plug.

  Other specific configurations of each part can be variously modified without departing from the spirit of the present invention.

  The present invention can be applied to a spark ignition internal combustion engine mounted on a vehicle or the like.

DESCRIPTION OF SYMBOLS 12 ... Ignition coil 13 ... Spark plug 132 ... Center electrode 133 ... 1st ground electrode 134 ... 2nd ground electrode, 3rd ground electrode 2 ... Electric field generation circuit

Claims (3)

A spark plug for a spark ignition internal combustion engine,
A central electrode electrically connected to both the ignition coil for applying a high voltage causing spark discharge and an electric field generating circuit for generating an electric field in the combustion chamber;
A first grounding electrode that is grounded;
A second ground electrode that is grounded and is positioned downstream of the first ground electrode along the gas flow direction in the combustion chamber, and the distance between the second ground electrode and the center electrode is A spark plug larger than the distance between the first ground electrode and the center electrode . A third grounding electrode that is grounded and is positioned upstream of the first grounding electrode along the gas flow direction in the combustion chamber, wherein a distance between the third grounding electrode and the central electrode is The spark plug according to claim 1, wherein the spark plug is larger than a distance between the first ground electrode and the center electrode . A spark plug for a spark ignition internal combustion engine,
A central electrode electrically connected to both the ignition coil for applying a high voltage causing spark discharge and an electric field generating circuit for generating an electric field in the combustion chamber;
A first grounding electrode that is grounded;
A second grounding electrode that is grounded and is positioned downstream of the first grounding electrode along the gas flow direction in the combustion chamber;
A spark plug that performs arc discharge only with the first ground electrode.

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