JP2008258077A - Spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug which efficiently facilitates the reaction of a fuel-air mixture in an internal-combustion engine to show high performance under a low required voltage. <P>SOLUTION: The spark plug 10 includes a main part composed of an insulator 5, a screw 4, a pedestal 3, a center electrode 1, a ground electrode 2, etc. The screw 4 is formed on a metal enclosure, and the pedestal 3, center electrode 1, ground electrode 2, etc., are inserted in a combustion chamber of each cylinder of an internal-combustion engine, such as an engine. The center electrode 1 is made covering a metal electrode 1b by coating an electron discharge film 1a, and the ground electrode 2 is made covering a metal electrode 2b by coating an electron discharge film 2a. Each of the electron discharge films 1a and 2a facilitates discharge of electrons therefrom to improve discharge characteristics between the electrodes. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a spark plug used for an internal combustion engine such as a gasoline engine for vehicles, and more particularly to a spark plug with improved ignition performance.

  Spark plugs play an important role in reliably igniting the air-fuel mixture and starting combustion in all operating conditions of the engine. Gasoline is difficult to ignite even at high temperatures, and the ignition performance of spark plugs is important to burn in a timely manner, and higher performance plugs are required to improve engine performance and reduce exhaust gas emissions. Yes.

  Many past technological developments of motorcycles and automobiles have focused on driving performance, such as improving the maximum output, but in recent years global warming due to carbon dioxide emissions, CO, HC, PM, NOx The demand for improving not only driving performance but also emission performance, such as prevention of environmental destruction due to harmful exhaust gases, is increasing.

The engine, which is an internal combustion engine, has a lower required voltage because it is accompanied by improved engine control accuracy toward direct injection, lean burn, high compression, and other technologies aimed at further improving fuel efficiency, using alternative fuels, and purifying exhaust gas. A spark plug with higher ignition performance is desired.
JP 2002-106382 A

  By the way, the ignition timing at which a high voltage is applied to the spark plug to generate a spark discharge and the mixture is ignited is controlled so that the engine output is always maximized. Since there is an ignition delay period before starting, it is set before the top dead center (TDC) of the piston.

  If the spark energy is not enough to ignite, or if the spark rise on the plug side is delayed, the mixture cannot be ignited and misfire occurs, or the piston passes the top dead center. Furthermore, the air-fuel mixture is ignited in the descending phase. As a natural result, the combustion pressure cannot be sufficiently obtained and the engine potential cannot be exhibited.

  When an ignition device having an ignition plug, an ignition coil, etc., interrupts the current flowing through the primary coil of the ignition coil by suddenly opening the switch with an interrupter (igniter) and shutting off the reverse voltage of the secondary coil. An electromotive force is generated. This voltage is distributed to a spark plug provided in each cylinder according to an ignition sequence by a distributor to generate a spark discharge between the electrodes of the plug.

  Since there is an insulating space between the electrodes of the spark plug, a high voltage is required, but electrostatic energy stored mainly in the stray capacitance of the secondary coil of the ignition coil is released by electric charges at the beginning of discharge. The energy density is high but the discharge time is very short. Subsequently, the electromagnetic energy stored in the secondary coil is released. Low energy density but long duration.

  The former is called capacitive discharge and the latter is called induction discharge. Thus, the spark discharge is a composite spark, and the capacitive discharge plays an important role in the activation and the induction discharge plays an important role in promoting the reaction. It is necessary for spark energy to be efficiently applied to the mixture, and for the reaction energy of the mixture to be efficiently transferred to the unburned mixture, so that a chain reaction must occur one after another. It is in contact with the electrode and has a property that it is difficult to spread due to heat deprivation (flame extinguishing action). The degree of growth of the flame kernel affects the quality of combustion.

  On the other hand, in order to alleviate the flame extinguishing action, the gap between the electrodes of the plug may be widened. However, if the gap between the electrodes is widened, a high voltage is required for discharging. Thus, a spark plug having a low required voltage and good ignition performance is required.

In addition, for reasons such as improving fuel efficiency for reducing CO _{2 and} reducing harmful exhaust gas generated in the combustion process, it is indispensable to complete combustion quickly in a predetermined period under all conditions.

  The present invention has been made to solve the above-described problems, and an object thereof is to efficiently promote the reaction of an air-fuel mixture in an internal combustion engine and provide a high performance spark plug with a low required voltage.

  In order to achieve the above object, an invention according to claim 1 is an ignition plug that ignites an air-fuel mixture by a spark discharge between electrodes, and emits electrons onto at least an electron emission side electrode among the electrodes. A spark plug characterized in that a release layer is formed.

  The invention according to claim 2 is characterized in that the electron emission layer is made of a material having an ionization energy lower than that of a metal constituting the electrode on which the electron emission layer is formed. Spark plug.

  The invention according to claim 3 is the spark plug according to claim 2, wherein the substance having low ionization energy is composed of a metal element or a compound containing a metal element.

  The invention according to claim 4 is the spark plug according to any one of claims 1 to 3, wherein the electron emission layer is formed for each of the electrodes. .

  According to the spark plug of the present invention, the electron emission layer that facilitates electron emission is formed on at least the electrode on the electron emission side of the electrode. Therefore, the reaction of the air-fuel mixture in the internal combustion engine can be efficiently promoted, and high-performance ignition can be realized with a low required voltage.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the structure of the spark plug of the present invention, and FIG. 2 shows an ignition circuit connected to the spark plug and the spark plug. The spark plug 10 is composed of main parts such as an insulator 5 made of an insulator and the like, a screw part 4 to be attached to a cylinder head (described later), a pedestal part 3, a center electrode 1 and a ground electrode 2. The screw portion 4 is formed in a metal casing, and is arranged in such a manner that the pedestal portion 3, the center electrode 1, the ground electrode 2 and the like are inserted into the combustion chamber 41 of each cylinder 40 of an internal combustion engine such as an engine.

  One end of the secondary coil 22 of the ignition coil is connected to the terminal 11 of the spark plug 10, and further connected to the center electrode 1 via the copper core (not shown) installed inside the insulator 5 and the pedestal 3. Is done. That is, the insulator 5 made of ceramic is formed at the lower portion of the terminal 11 so as to cover the copper core. On the other hand, the ground electrode 2 is grounded via the cylinder head portion of the cylinder 40.

  A copper core is connected to the terminal 11, and a truncated cone base 3 is connected to the copper core. The pedestal portion 3 is made of a conductive material having excellent heat resistance and corrosion resistance, such as Inconel, and the pedestal portion 3 is made of iridium or an alloy thereof by welding with a diameter of 0.4 mm to 0.7 mm and a length ( A columnar center electrode 1 having a height of 1.1 mm is connected. Therefore, the terminal 11 is connected to the center electrode 1 to form a discharge voltage conductive path.

  The ground electrode 2 is made of a metal made of platinum, for example, and is connected to a metal casing of the spark plug by welding or the like. At this time, a gap of a predetermined distance, for example, 1.1 mm is formed between the center electrode 1 and the ground electrode 2.

  Here, the detection of the ion current using the spark plug 10 will be briefly described. FIG. 1 is a circuit diagram showing an ionic current detection circuit and the like among an ignition circuit for generating a spark in the spark plug 10 and an ionic current detection device for detecting the generated ionic current.

  The spark plug 10 is disposed at a position facing the cylinder head portion of each cylinder 40 of the internal combustion engine, and the pedestal portion 22, the center electrode 1, and the ground electrode 2 are exposed to the combustion chamber 44. The ignition coil for generating a discharge voltage in the spark plug 10 includes a primary side (low voltage side) coil 21 and a secondary side (high voltage side) coil 22, and one end of the primary side coil 21 is It is connected to a DC power source 25 such as a battery power source, and the other end is grounded via a power transistor 23 that is opened and closed according to an ignition signal from an ECU (electronic control unit) 24.

  One end of the secondary coil 22 is connected to the terminal 11 of the spark plug 10 through a high tension cord, and further, a copper core (not shown) running in the insulator 5 and the center through the pedestal 3. Connected to electrode 1. On the other hand, the ground electrode 2 is grounded via the cylinder head portion of the cylinder 40.

  On the other hand, the ion current detector 30 is connected to the other end of the secondary coil 22. The ion current detection unit 30 surrounded by a broken line is connected in parallel with a capacitor 35 charged to the polarity shown in the figure by a discharge current, and a Zener diode 32 that defines the charging voltage of the capacitor 35. The Zener diode 32 is grounded via a resistor 34 and the Zener diode 32 is grounded via a diode 33 that prevents backflow of current.

  The ECU 24 is composed of a microcomputer, and is arranged in the vicinity of a crankshaft or a camshaft (both not shown) to output a signal corresponding to a TDC position of each cylinder and a crank angle obtained by subdividing the TDC position and an intake air. An output of a sensor group such as an absolute pressure sensor that outputs a signal corresponding to the in-pipe absolute pressure (PBA) is input.

  The current flowing from the power source 25 through the primary coil 21 is energized / interrupted by opening / closing (ON / OFF) of the power transistor 23 according to an ignition signal (ignition command) from the ECU 24. When the power transistor 23 is turned from the on state to the off state and the current in the primary side coil 21 is cut off, a negative high voltage (back electromotive force) is generated in the secondary side coil 22 accordingly, and the discharge current Flows as shown by a one-dot chain line in FIG.

  Specifically, the secondary coil 22, the capacitor 35 or the Zener diode 54, and the diode 33 flow in order from the spark plug 10, and spark discharge is generated in the gap between the center electrode 1 and the ground electrode 2 of each spark plug 10. The mixture is ignited and burned.

  The discharge current described above charges the capacitor 35 with the polarity shown. The charged capacitor 35 functions as an ion current detection power source having a bias voltage for detecting the ion current. When the air-fuel mixture burns by spark discharge in the gap between the electrodes of the spark plug 10, the air-fuel mixture (more precisely, the combustion gas generated by the combustion of the air-fuel mixture) is ionized to generate ions. As ions are interposed between the pedestal 3 and the center electrode 1 and the ground electrode 2 and the electrical resistance in the vicinity of the gap between the electrodes decreases, as shown by the dotted line in FIG. An ion current that flows in the order of the secondary coil 22 and the spark plug 10 is generated. At this time, the voltage value at the detection resistor 34 is changed by being dragged by the generated ion current. The ion current detector 30 detects the change in the voltage value, that is, the ion current waveform, analyzes it by a computer or the like, determines whether the internal combustion engine is in a misfire state, and performs misfire detection.

  By the way, in the configuration of the present invention, the center electrode 1 is covered with the electron emission film 1a so as to cover the metal electrode 1b constituting the electrode, while the ground electrode 2 is also provided with the metal electrode 2b constituting the electrode. The electron emission film 2a is covered so as to cover it. The electron emission films 1a and 2a are made of a material containing an element having a lower ionization energy or an element having a lower work function than the elements constituting the metal electrodes 1b and 2b. By configuring the electrodes in this way, electrons are easily emitted from the electron emission films 1a and 2a, and the discharge characteristics between the electrodes can be improved.

  Specifically, for example, platinum (Pt) is used for the metal electrode 2 b of the ground electrode 2, and iridium (Ir) is used for the metal electrode 1 b of the center electrode 1. Pt is 870 kJ / mol, and Ir is 880 kJ / mol. Therefore, a compound containing Na (sodium) having an ionization energy lower than these ionization energies can be used for the electron emission films 1a and 2a. Actually, sodium silicate was formed as the electron emission films 1a and 2a. The ionization energy of Na is 496 kJ / mol.

  In order to form this, for example, an electroplating method was used. The electrode portion of the spark plug was immersed in a sodium silicate aqueous solution as a cathode, and direct current electricity was applied to deposit metal ions in the aqueous solution on the surface of the electrode.

  Note that a single element may be composed of a single element as long as it can be coated on a metal electrode. This makes it easier for electrons to be emitted from the electron-emitting film 1a or 2a, making it easier for discharge to start, and continuing to emit electrons from the metal electrode 1b or metal electrode 2b. Can be performed early and smoothly shift to induction discharge, and the discharge characteristics between the electrodes are improved.

  Further, in FIG. 1, an electron emission film is formed on both the metal electrode 1b and the metal electrode 2b in the center electrode 1 and the ground electrode 2, but the electrode that emits electrons during discharge, in this case the metal electrode 1b, The electron emission film may be formed only on the metal electrode 1b instead of covering the entire surface of the metal electrode 1b. Further, the electron emission film may be formed so as to cover all the portions exposed to the combustion chamber 41, for example, all the upper surfaces of the metal electrode 1 b and the metal electrode 2 b and the pedestal portion 3.

  In order to explain the operation of the present invention, FIG. 3 shows a typical voltage waveform during discharge in the secondary coil 22. Spark discharge is discharge that occurs when high voltage generated in the ignition coil breaks the insulation between the electrode gaps of the spark plug. As shown in FIG. 3, the spark discharge is composed of two components, a capacitive discharge A and an induction discharge B. As shown in FIG. 2, in the ignition by the transistor 23, the back electromotive force generated in the coil 22 on the secondary winding side of the ignition coil is stored in the stray capacitance that is naturally generated between the coil, the plug cord, and the like and the ground. When the charge voltage of the stray capacitance reaches or exceeds the discharge voltage of the electrode gap, the charge accumulated in the stray capacitance is discharged. This is called capacitive discharge A. Since the stray capacitance is generally very small, for example, a large current of about 30 to 50 A flows for a short time (for example, about 10 to 20 ns), and the capacitive discharge is completed.

  Next, a discharge current due to electromagnetic energy stored in the coil 22 on the secondary winding side flows between the electrode gaps. However, since the inductance of the coil 22 is large, the current value is small (for example, 50 to 80 mA) and a relatively long time. The discharge continues (for example, 1 to 3 ms), and this is called induction discharge B. Finally, the region where the excess electric energy is attenuated by the induction discharge is the damped oscillation C.

  At this time, fuel particles between the electrodes are ionized and activated by the capacitive discharge A, and energy is supplied by the subsequent induction discharge B so that the chemical reaction started at this time is continuously developed. The induction discharge B plays a role of supplying heat until the flame kernel generated by the first chemical reaction spreads to the surrounding air-fuel mixture and becomes large enough to spread the combustion by itself. Therefore, the role of the induction discharge B is important, and it is desirable that the discharge time is long to some extent while maintaining a constant induction discharge voltage.

  4 to 6, the high voltage generated from the secondary coil 22 is applied to the spark plug, and the state of the discharge current flowing in the insulating space between the center electrode and the outer electrode (ground electrode) of the spark plug is measured. did. 4 to 6, the horizontal axis represents time, and the vertical axis represents the discharge current value. FIG. 6 shows the discharge current of a spark plug that has been used for a long period of time. The waveform has a long falling interval (corresponding to a time constant in terms of an electric circuit), and it takes time for a stable current to flow. I understand. FIG. 5 shows the discharge current of a new spark plug. In the new spark plug, although the falling interval is shorter than that of the used point plug shown in FIG. 6, there is still a delay in stabilization.

  FIG. 4 shows an example in which an electron emission film is formed on an electrode of an ignition plug as in the present invention, but the waveform of the discharge current is sharper than that of the new ignition plug of FIG. It can be seen that the time when the current suddenly falls and a stable current flows increases. That is, by adopting the configuration of the present invention, it is possible to shift from capacitive discharge to induction discharge quickly and smoothly, and to secure a long induction discharge time.

  Next, in order to further support the data, the secondary voltage waveform in the secondary coil 22 was measured with an oscilloscope, and the respective characteristics were compared. The secondary voltage waveform was measured in an idling state. 7A shows a secondary voltage waveform in a new but conventional spark plug (hereinafter referred to as an unprocessed new plug), and FIG. 7B shows a new spark plug (hereinafter referred to as a new spark plug according to the configuration of the present invention). The secondary voltage waveform in the new plug after processing) is shown. In the figure, A indicates the above-described capacity discharge region, B indicates the induction discharge region, and one scale of the time axis is 10 μs.

  As shown in FIG. 7 (a), in the unprocessed new plug, there is a waveform disturbance considered to be due to electric resistance in the capacity discharge region A at the initial stage of discharge. ) There is no disturbance as you can see. In other words, in the new plug after processing, the capacity discharge at the initial stage of discharge becomes easier to emit electrons due to the processing (processing) of the plug body, the spark discharge between the electrodes becomes smooth, and the resistance is reduced and discharged in one machine. It is presumed that the secondary voltage decreases quickly.

  Moreover, a big difference can be confirmed in the induction discharge area | region B in FIG. 7 (a) and (b). Inductive discharge that follows capacitive discharge becomes a small current due to factors such as electrical resistance between the electrodes in the unprocessed new plug, and the voltage decreases as shown in the region B-1, and the spark is temporarily stopped. it is conceivable that. In the new plug after processing, as shown in the area B-2 in FIG. 7B, the induced discharge voltage after the capacitive discharge is stable, and the spark discharge between the electrodes continues.

  As described above, in order to grow the flame kernel of the air-fuel mixture and give sufficient ignition power to the lean air-fuel mixture, it is necessary that the discharge duration is long to some extent in the induction discharge region B with a stable discharge voltage. However, these conditions can be achieved as described above by configuring the spark plug according to the present invention.

  Next, comparison data when the configuration of the present invention is applied to a used spark plug (hereinafter referred to as a used plug after processing) is shown. Spark plugs are more likely to discharge if there are corners even in the gap between the same electrodes. When the plug is used for a long period of time, the electrode shape is rounded due to wear, so that it becomes difficult to discharge and misfires easily. In addition, the gap between the electrodes is consumed and gradually widened, and the required voltage increases.

  12A shows the secondary voltage waveform of a new plug that has not been processed, FIG. 12B shows the secondary voltage waveform of a new plug that has been processed, and FIG. 13 shows the secondary voltage waveform of a used plug that has been processed. Indicates. One scale of these time axes is 20 μs. In addition, the used plug after processing is obtained by processing a used spark plug that has traveled about 20000 km so as to have the configuration of the present invention in order to see the influence of electrode consumption.

  The comparison between FIG. 12 (a) and FIG. 12 (b) is the result as described in FIG. 7, but as can be seen from the comparison between FIG. 13 and FIG. Even if the electrode is consumed, the configuration of the present invention shows a waveform very similar to the secondary voltage of the new plug after processing, and it can be seen that the ignition performance is remarkably improved.

  In addition, FIGS. 8 to 10 and 11 show the measurement by changing the scale of the time axis so that a new plug after processing, an unprocessed new plug, and a used plug after processing can be compared better. FIG. 8 is a secondary voltage waveform using a new plug after processing, and one time scale is 50 μs, and FIG. 9 is a secondary voltage waveform using a new plug after processing. One scale is 5 μs, and FIG. 10 is a secondary voltage waveform using a used plug after processing. One scale on the time axis is 5 μs. FIG. 11 is a secondary voltage waveform using a used plug after processing, and one scale of the time axis indicates 10 μs.

  As described above, the plug of the present invention maintains a stable spark discharge even after the required voltage is lowered, the electrode is consumed and the gap is widened, and the flame extinguishing action is mitigated because the discharge density is high. In addition, an inexpensive general electrode plug using a nickel alloy can perform more than a high performance plug using an expensive noble metal as an electrode.

  In the positive column during arc discharge, which is short-circuited between the plug electrode gaps at a high voltage, negatively charged electrons and positively charged positive ions are mixed at approximately the same rate. The charged particle county has irregular thermal motion. This discharge gas radiates heat and activates the fuel particles. In order to ignite the air-fuel mixture, it is necessary to maintain the plasma state for a certain period of time. However, the plasma that has lost its heat returns to neutral molecules and is no longer in a plasma state, becoming an insulator and conducting electricity. It is necessary to maintain the plasma generation environment between the electrodes with the supply of.

  In the configuration of the present invention, when a high voltage is applied to the electrode by forming an electron emission layer (film) on the electrode that is easy to emit electrons in the insulating space between the electrodes in the conductor constituting the plug, Is released and bridges between the electrodes, promoting the action of spark discharge of the spark plug. When a strong electric field is generated on the electrode, a large amount of electrons are emitted from the electrode surface to help spark discharge of the plug, the electrodes are connected by a conductive discharge path, and the spark discharge is sustained for a long time as an induced discharge by a stable current. be able to. This induction discharge is stable, and the gas temperature is high and the discharge time is long, so that it plays a big role in the growth of flame nuclei and the propagation of flame to spread the combustion.

  In addition, it is advantageous in terms of electrode consumption, and when a conventional plug is worn out and the gap widens, a high required voltage is required for spark discharge, but the plug of the present invention has another electron emission source. Misfires (cannot be discharged) after electrode consumption is reduced.

For example, if low-speed running and stopping are repeated frequently in winter, steam and carbon that does not burn will adhere to the plug, causing high voltage to travel through the carbon, causing leakage and no spark discharge. The environment is also worsened by carbon adhesion. In order to keep the electrodes in good condition, a good plasma state is required while the engine is running. This is a good spark, and maintaining this state depends on the performance (state) of the spark plug, and the running performance changes depending on the maintenance of the combustion chamber environment of the engine. Although the engine life is greatly affected, the above problem can be solved by using the plug of the present invention.

It is a figure which shows the structure of the ignition plug of this invention. It is a figure which shows the connection state of a spark plug, an ignition circuit, etc. It is a figure which shows the typical shape of the voltage waveform of spark discharge. It is a figure which shows the electric current waveform of the spark discharge at the time of using the ignition plug of this invention. It is a figure which shows the electric current waveform of a spark discharge in the case of using a new spark plug and a conventional spark plug. It is a figure which shows the electric current waveform of the spark discharge in the case of using a used and conventional spark plug. It is the figure which compared the secondary side coil voltage waveform by the case where the spark plug of this invention is used, and the case where the conventional spark plug is used. It is a figure which shows the secondary voltage waveform of the new plug of the structure of this invention. It is a figure which shows the secondary voltage waveform of the new plug of the structure of this invention. The secondary voltage waveform of what used the structure of this invention with respect to the used plug is shown. The secondary voltage waveform of what used the structure of this invention with respect to the used plug is shown. The secondary voltage waveform of the conventional new plug and the secondary voltage waveform of the new plug of the structure of this invention are shown. The secondary voltage waveform of what used the structure of this invention with respect to the used plug is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Center electrode 1a Electron emission film 1b Metal electrode 2 Ground electrode 2a Electron emission film 2b Metal electrode 3 Base part 4 Screw part 5 Insulator 10 Spark plug

Claims (4)

A spark plug that ignites an air-fuel mixture by spark discharge between electrodes,
An ignition plug characterized in that an electron emission layer for emitting electrons is formed on at least an electrode on the electron emission side of the electrodes.   The spark plug according to claim 1, wherein the electron emission layer is made of a material having lower ionization energy than a metal constituting the electrode on which the electron emission layer is formed.   3. The spark plug according to claim 2, wherein the substance having low ionization energy is composed of a metal element or a compound containing a metal element. The spark plug according to any one of claims 1 to 3, wherein the electron emission layer is formed for each of the electrodes.

Images