Patent Grant
8528531
Apparatuses consistent with the present disclosure relates to an ignition apparatus of a plasma jet ignition plug for an internal combustion engine performing the ignition of mixed gas by forming plasma.
In the related art, a spark plug performing a firing of mixed gas by spark discharge (simply referred to as ‘discharge’) is used for an igniting plug of an engine, for example, an internal combustion engine of automobiles. In recent years, a plasma jet ignition plug in which the expansion of combustion is speedy and which can be surely fired for lean mix gas having high igniting limit fuel efficiency has been used as an ignition plug since a high output and low fuel efficiency of an internal combustion engine are required.
In such a plasma jet ignition plug, a spark discharge gap between a center electrode and a ground electrode is formed when connected to an electric source. A plasma jet ignition plug surrounds a vicinity of this spark ignition gap using an insulator such as ceramics, and thus has a structure forming a discharge space of small volume called a cavity. A plasma jet ignition plug using an overlap type electric source is described with reference to one example (e.g., see patent document 1). In an ignition of mixed gas, first, a high voltage is applied between a center electrode and a ground electrode, and then a spark discharge (also called ‘trigger discharge) is produced. Due to dielectric breakdown produced at the time of spark discharge, a current can flows between both electrodes through a relatively low voltage. Thus, more energy is provided, thereby transiting a discharge status, and therefore plasma is formed in the cavity. Further, the formed plasma is extruded through a communicating hole, so that an ignition of nixed gas is performed. One effusion of plasma corresponds to each stroke.
In such a plasma jet ignition plug, a higher current than typically used to spark discharge in a general spark plug is required to flow through the spark discharge gap when plasma is formed. In order to increase a flowing current, it is necessary to lower the electric resistance value of the circuit through which the current flows, and normally a resistor is no provided in the circuit of an ignition apparatus or inside the plasma jet ignition plug (e.g., see patent document 2).
However, since in a plasma jet ignition plug, high current flows in a short time, fluctuations in a current value per unit time are significant. Therefore, there can be a problem a large amount of electrical noise being easily (in this specification, noise, such as electric waves radiating outside from an appliance, is sometimes called ‘electrical noise’. When a high frequency current flows within an electronic appliance, this electric noise is radiated, and affects external appliances or other signals with interference) attributable to stray capacity (the stray capacity is formed at a high voltage line positioned between a plasma jet ignition plug and a discharge voltage application unit applying a voltage to that plasma jet ignition plug). To suppress the occurrence of such electric noise, a resistor may be provided inside the plasma jet ignition plug or on a circuit of an ignition apparatus to suppress energy accumulated as stray capacity, but if a resistor is provided directly, a discharge current producing capacity is smaller, thus causing uncertainty whether an energy capacity discharge of sufficient size to form plasma will be obtained.
The present invention has been made considering the above facts, and it is an object of exemplary embodiments to provide an ignition apparatus of a plasma jet ignition plug that produces a current of sufficient size to form plasma but suppressing the occurrence of electric noise, at the ignition of the plasma jet ignition plug.
To achieve the above-described objective, an ignition apparatus of a plasma jet ignition plug of the invention is characterized by the following (1)˜(4).
(1) An ignition apparatus of a plasma jet ignition plug, comprising:
a plasma jet ignition plug including an insulator having an axis hole that extends in an axial direction and a center electrode in the axis hole, a metal shell having a cylindrical shape and holding the insulator, and a ground electrode having a plate shape and having a communication hole that communicates along the axial direction in its center;
a discharge voltage application unit applying a voltage for providing a spark discharge in a spark discharge gap, which is formed between the center electrode and the ground electrode, to the plasma jet ignition plug; and
a diode disposed between the plasma jet ignition plug and the discharge voltage application unit;
wherein
the ignition apparatus further includes:
a resistor, wherein one end of the resistor is connected to the diode and the other end of the resistor is electrically connected to the center electrode of the plasma jet ignition plug; and
a capacitor functional component, wherein one end of the capacitor functional component is electrically connected to the center electrode of the plasma jet ignition plug and the other end of the capacitor functional component is grounded.
(2) The ignition apparatus according to the above (1),
wherein
the capacity functional component includes:
a terminal fitting electrically connected to the center electrode of the plasma jet ignition plug, and
a metal cask having a hollow cylindrical shape and receiving the terminal fitting in an inside of the metal cask.
(3) The ignition apparatus according to the above (2),
wherein
the capacitor functional component has a dielectric filing a gap between the terminal fitting which is received in the metal cask and the metal cask.
(4) The ignition apparatus according to the above (2) or (3),
wherein
the other end of the resistor is disposed inside the metal cask,
wherein electrostatic capacity is accumulated on an area sandwiched between a cross-section of the metal cask, where the other end of the resister is included, perpendicular to an axis center direction of the metal cask and a cross-section of the metal cask containing an end face of the metal cask,
wherein the terminal fitting is disposed inside the area, and
wherein the electrostatic capacity in the area is more than 1 pF and less than 100 pF.
According to an ignition apparatus of a plasma jet ignition plug of the above (1) construction, at the ignition of a plasma jet ignition plug, a current of sufficient size for forming plasma flows at a spark discharge gap and also occurrence of electric noise is reduced.
According to an ignition apparatus of a plasma jet ignition plug of the above (2) construction, because with respect to electric noise attributable to a newly provided capacitor, a metal cask forming the capacitor acts to shield, and the propagation of electric noise producing from the capacitor may be suppressed.
According to an ignition apparatus of a plasma jet ignition plug of the above (3) construction, by using dielectric of a desired dielectric constant, the miniaturization of this capacitor functional component may be realized.
According to an ignition apparatus of a plasma jet ignition plug of the above (4) construction, at the ignition of a plasma jet ignition plug, a current of sufficient size for forming plasma effectively flows in a spark discharge gap and also occurrence of electric noise is more effectively prevented.
According to an ignition apparatus of a plasma jet ignition plug of the present invention, at the ignition of a plasma jet ignition plug, a current of sufficient size for forming plasma flows at a spark discharge gap and also occurrence of electric noise is prevented.
As described above, the present invention has been concisely described. Also, by carefully reading the following described preferred embodiments in reference to the annexed drawings, the details of the invention will be further elucidated.
Hereinafter, one embodiment of an ignition apparatus for a plasma jet ignition plug according to the present invention will be described with reference to drawings. First, a plasma jet ignition plug 100 will be described. A basic structure of a plasma jet ignition plug 100 usable in an ignition apparatus 200 of the present invention is shown in
The plasma jet ignition plug 100 shown in
At the inner part of the electrode reception part 15, a bar-type center electrode 20, which uses Cu or Cu alloy as a center material and has Ni alloy as a shell is provided. A structure formed by bonding a discus-type electrode tip 25, which is formed of an alloy having noble metal or W as a main ingredient, at the front end of the center electrode 20 or is formed integrally with the center electrode 20 may also be used (in the present embodiment, a formation of the center electrode 20 integrated with the electrode tip 25 is also called the ‘center electrode’). Herein, a low volume discharge space is enclosingly formed at an inner-rim of the electrode reception part 15 of the shaft hole 12, and the front end surface of the center electrode 20 (or, a front end surface of an electrode tip 25 integrally bonded to the center electrode 20). In the present embodiment, this discharge space is called a cavity 60. Also, the center electrode 20 extends toward a back end side in the shaft bore 12, and electrically connected to a terminal fitting 40 provided at the back end side of the shaft bore 12 via a conductive sealed body formed of mixture of metal and glass. The terminal fitting 40 is connected to a high-voltage cable (not shown) through a plug cap (not shown), and constructed to receive a high-voltage from a later-described ignition apparatus 200 (see
Also, a part of the insulator 10 from a portion of the back end side body section 18 to the long leg part 13 is supported by a metal shell 50 that is formed in a tubular shape using ferrous material, and the insulator 10 is supported by the crimping portion of the metal shell 50. The metal shell 50 has a screw attachment part 52 having a screw thread for screw connection with an attachment hole 301 of the engine head 300. Further, a proximal end side of the attachment screw part 52 is surrounded by a ring-shape gasket 5 to prevent a leakage of air tightness inside the engine through the attachment hole, when the plasma jet ignition plug 100 is attached to the attachment hole of the engine head 300.
A front end of the metal shell 50 is provided with a disk shaped ground electrode 30 formed using Ni alloy having a superior spark-proof composition such as INCONEL™ 600 or 601. The ground electrode 30 is integrally bonded with the metal shell 50, in a state that the ground electrode 30 contacts the front end surface 16 of the insulator 10 with its thickness direction oriented in a line with the axis direction O. The center of the ground electrode 30 is formed with a communication hole 31, axially aligned with the opening part 14 of the cavity 60, and through this communication hole 31 the inner part of the cavity 60 communicates with the open air. Between the ground electrode 30 and the center electrode 20 is formed as a spark discharge gap, and the cavity 60 is formed to enclose at least this part. When a spark discharge is performed in this spark discharge gap, energy is supplied so that plasma is formed in the cavity 60, and this plasma is extruded from the opening part 14 through the communication hole 31.
In addition to components shown in
The tubular electrode 111 is comprised of conductive metal material, and formed to have a hollow structure with a tubular shape. The inner diameter of the tubular electrode 111 is greater than a diameter of the back end side body part 18 of the insulator 10. The tubular electrode 111 is disposed to enclose and surround the back end side body part 18 of the insulator 10 and disposed the center axis of the tubular electrode 111 aligned with the center axis of the back end side body part 18. As illustrated in
A space between either the insulator 10 or the terminal fitting 40 and the tubular electrode 111 is filled with dielectrics 112. The dielectric 112 is comprised of electric insulators having dielectric properties. The dielectric 112 is comprised of higher dielectric material than the insulator 10.
The terminal fitting 40 of the conductor and the tubular electrode 111 enclosing the conductor face each other with the dielectric interposed there between, thereby which electrostatic capacity, i.e. a circuit component corresponding to the capacitor C1 shown in
Originally, for example, a member, such as the terminal fitting 40, and a ground side, such as the ground electrode 30, is formed with a relatively small stray capacity (not shown) there between. The stray capacity greatly affects a discharge action in the plasma jet ignition plug 100. In the present embodiment, in order to provide a more secured discharge action, the tubular electrode 111 and the dielectric 112 are provided. Thus, by providing the tubular electrode 111 and the dielectric 112, a capacitor C1 having a larger value than the stray capacitor is formed in the vicinity of the center electrode 20.
As illustrated in
As illustrated in
When an electric discharge occurs at the plasma jet ignition plug 100, high-frequency current flows through the circuit including the terminal fitting 40, in a short time and electrical noise caused by the high-frequency current, that is electric waves, radiates out of the plasma jet ignition plug 100 to affect the surrounding electronic devices. However, with respect to noise occurring nearby the terminal fitting 40, which surrounded and covered with a grounded tubular electrode 111, the radiation of the noise toward the outside is steeply suppressed by an electrostatic shield effect.
The plasma jet ignition plug 100 having such a structure forms plasma in the cavity 60 by connecting to the ignition apparatus 200 shown in
As shown in
The high-voltage generation circuit 210 shown in
A control terminal of the transistor Q1, that is a base electrode, is applied with an ignition coil electric current signal from a control circuit that is not shown. The ignition coil electric current signal is a signal having one pulse signal per 1 discharge cycle in the plasma jet ignition plug 100, and used in a switching control of the transistor Q1.
Thus, when the ignition coil current signal becomes a high-level, the transistor Q1 conducts, and current flows to the primary coil L1 of the ignition coil 211 from power supplied by the DC source 230. Also, when the ignition coil current signal becomes a low-level, the transistor Q1 does not conduct, and the current flowing through the primary coil L1 of the ignition coil 211 is abruptly blocked.
When a current starts to flow through the primary coil L1 of the ignition coil 211, and when the current of the primary coil L1 of the ignition coil 211 is blocked, a high-voltage is produced at the secondary coil L2. The voltage producing at the secondary coil L2 is determined by a ratio of the winding number of the primary coil L1 and the secondary coil L2.
As shown in
A capacitor C2 is connected between an output terminal and a ground terminal of the high-voltage generation circuit 220. Also, the output terminal of the high-voltage generation circuit 220 is connected with one end of a coil L3, and the other end of the coil L3 is connected with one end of the diode D2, that is a cathode terminal, and the other end of the diode D2, that is an anode terminal, is electrically connected to the terminal fitting 40 of the plasma jet ignition plug 100. The diode D2 is provided to prevent the counter-flow of a current. That is, in order to ensure current at plasma discharge flows only in a direction from the terminal fitting 40 towards the output side of the high-voltage generation circuit 220 by a negative voltage, the diode D2 controls polarity. Further, a DC resistive value such as the coil L3 in a wiring connecting a capacitor C2 to the terminal fitting 40 of the plasma jet ignition plug 100 is less than 1Ω.
A specific example of waveforms of a discharge current flowing at discharge and a discharge voltage applied to the plasma jet ignition plug 100 during one cycle of a discharge action are shown in
When a discharge is started, first in order to produce a spark discharge (referred to as a trigger discharge), a high-voltage from the high-voltage generation circuit 210 is supplied to the plasma jet ignition plug 100. That is, the transistor Q1 shown in
Electrostatic capacity other than the capacitor C1, i.e. stray capacity, exists between electrodes inside the plasma jet ignition plug 100, between the ground and a high-voltage cable (a wiring including D1, R1) connecting the high-voltage generation circuit 210 and the plasma jet ignition plug 100, and between the secondary coil L2 of the ignition coil 211 and the ground.
When the output 210a of the high-voltage generation circuit 210 instantly has a high-voltage, electric charge is accumulated at each point of stray capacity or the capacitor C1 by the high-voltage. In an initial stage of the plasma jet ignition plug 100 (a timing of ‘capacity discharge’ shown in
Meanwhile, to produce plasma by discharge, it is necessary to supply high electric energy into the plasma jet ignition plug 100. Because a current that can be supplied from the high-voltage generation circuit 210 to the plasma jet ignition plug 100 is relatively small, energy to produce plasma is supplied from the high-voltage generation circuit 220 of a separate circuit. Actually, power outputted by the high-voltage generation circuit 220 is accumulated on the capacitor C2, and then electric charge of the capacitor C2 is supplied through the diode D2 and the coil L3 into the plasma jet ignition plug 100. When performing a plasma discharge subsequent to the spark discharge, an electric discharge production becomes easy by a dielectric breakdown occurring at the spark discharge, so that a discharge can continue even at a relatively low voltage.
When a negative voltage applied to the terminal fitting 40 of the plasma jet ignition plug 100 from the high-voltage generation circuit 210 side is smaller than a negative voltage appearing at terminals of the capacitor C2 connected to the high-voltage generation circuit 220, the diode D2 conducts, and electric charge accumulated on the capacitor C2 is supplied into the plasma jet ignition plug 100 through the diode D2 and the coil L3. That is, a current (also called plasma current) flowing by plasma occurring in the cavity 60 of the plasma jet ignition plug 100 dribbles into the capacitor C2 via the diode D2 and the coil L3 from the terminal fitting 40.
Thus, as the waveform shown in the discharge current I11 of
However, during the timing of ‘capacity discharge’, a high-amplitude high-frequency current electric charge caused by of a high-voltage appears for a very short time on a waveform of a discharge current. When noise such as electric waves radiates from the high-frequency current, the radiated noise adversely affects electronic devices surrounding the ignition apparatus 200. Therefore, noise radiated from the ignition apparatus 200 needs to be prevented.
In the ignition apparatus 200 having a construction as shown in
In the meantime, when a current at ‘capacity discharge’ is small, it is difficult for plasma current to flow into the plasma jet ignition plug 100 at a plasma discharge. That is, when a current of ‘capacity discharge’ is small, a time needed to emit electric charge accumulated on the points of stray capacity gets longer, and a time in which a negative high-voltage applied to the plasma jet ignition plug 100 from the high-voltage generation circuit 210 side decays becomes longer. If this high-voltage has not sufficiently decayed, the diode D2 does not conduct, so that it is impossible to supply electric charge of the capacitor C2 to the plasma jet ignition plug 100 for plasma discharge.
Also, for a plasma current through line (a current path having the diode D2, the coil L3, etc.), it is desirable to keep a DC resistor small. By this, a peak value of the plasma current becomes larger, so that a production efficiency of plasma is improved.
A resistor R1 inserted between the output of the high-voltage generation circuit 210 and the terminal fitting 40 of the plasma jet generation plug 100 suppresses an amplitude of a high-frequency current flowing at ‘capacity discharge’ by a high-voltage cable connecting the high-voltage generation circuit 210 and the plasma jet ignition plug 100 and electric charge accumulated on stray capacitance of the secondary coil L2 of the ignition coil 211, thereby having an effect of saving the above-described noise.
However, by providing the resistor R1, a current at ‘capacity discharge’ becomes smaller, a time until when a high-voltage applied to the terminal fitting 40 decays as described above becomes longer, and it is difficult to flow a current of the capacitor C2 into the plasma jet ignition plug 100 at a plasma discharge.
As illustrated in
Therefore, the capacitor C1 needs to be disposed at a position near the terminal fitting 40 rather than the resistor R1. In addition, since a very high voltage is applied from the high-voltage generation circuit 210, a high internal pressure (several tens of kV) is required for the capacitor C1. Due to this, it is difficult to use a general capacitor selling on the market as the capacitor C1. Thus, as shown in
For electrostatic capacity of the capacitor C1, more than 1 pF and less than 100 pF is suitable. In particular, as shown in
Meanwhile electric charge is also accumulated in an area sandwiched between a cross-section S0 of the tubular electrode 111 containing the cross-section of the tubular electrode 111 (a cross-section containing a cross-section of the tubular electrode 111 at the side to which the plasma jet ignition plug 100 is not inserted and penetrated, positioned opposite to the above-described cross-section S2) and the above-described cross-section S1 of the tubular electrode 111. However, electric energy by discharge of this electric charge is supplied to the resistor R1 placed in this area, but not supplied to the plasma jet ignition plug 100. Because of this, in order to make it easy for a current of the capacitor C2 to flow at plasma discharge into the plasma jet ignition plug 100, it is significantly necessary to take action by emitting electric charge accumulated in an area sandwiched between the above-described cross-section S1 and the cross-section S2), and thus, it is proper that electrostatic capacity accumulated in the area is more than 1 pF and less than 100 pF.
Electrostatic capacity accumulated in an area between the above-described cross-section S1 and the cross-section S2 may be, for example, specified by cutting a part from the cross-section S0 to the cross-section S1 of the tubular electrode 111 and measuring electrostatic capacity of the remaining tubular electrode 111 by an LCR meter. On the one hand, a method of specifying electrostatic capacity is not limited to this. It may be theoretically calculated in reference to a shape and its inner dielectric of the tubular electrode 111, a position of the other end of the resistor R1 inside the tubular electrode 111, and a shape and its dielectric of the plasma jet ignition plug 100 placed inside the tubular electrode 111.
In a case electrostatic capacity of the capacitor C1 is less than 1 pF, an effect of the capacitor C1 is not sufficiently obtained, but it is difficult for a current of the capacitor C2 to flow at plasma discharge into the plasma jet ignition plug 100. Specifically, in a case electrostatic capacity of the capacitor C1 is less than 1 pF, a probability that plasma is formed in the cavity 60 (plasma occurrence probability) is lowered to 70˜80%. Also, in a case electrostatic capacity of the capacitor C1 exceeds 100 pF, when a high-voltage from an output of the high-voltage generation circuit 210 is applied to the terminal fitting 40, a rising velocity of a voltage slows by a relaxation time of R1, C1, and it may not be possible for capacity discharge. Specifically, in a case electrostatic capacity of the capacitor C1 exceeds 100 pF, a probability that capacity discharge occurs by the plasma jet ignition plug 100 (discharge probability) lowers to 70-80%. On the one hand, when electrostatic capacity of the capacitor C1 is more than 1 pF and less than 100 pF, both a plasma occurrence probability and a discharge probability can be a high-level, that is 80-100%.
For an electrode constructing the capacitor C1, it is not limited to a cylindrical-shape such as the tubular electrode 111, but for example, an electrode of metal having a plane shape is also possible. However, in a case of using an electrode enclosing the surrounding of the terminal fitting 40 such as the tubular electrode 111 and grounding this, an effect of electrostatic shield can be obtained. That is, because an electric potential of the tubular electrode 111 is constant, noise occurring by a high-frequency current flowing through a part such as the terminal fitting 40 may not radiate to the outside of the tubular electrode 111. Noise occurring at ‘capacity discharge’ by stray capacitance existing in the secondary coil L2 of the ignition coil 211 or a high-pressure cable, because a current is suppressed by an effect of the resistor R1, becomes relatively smaller. It is suitable that a resistive value of the resistor R1 is more than 100Ω.
To sufficiently lower noise by an effect of the resistor R1, it is desirable that a length of a current path through which a high-frequency current flows that can cause noise may possibly shorten. Specifically, for a wiring distance from a fitting part of the plasma jet ignition plug 100 and the engine head 300 to the resistor R1, and a wiring distance from the fitting part to the diode D2, each may be less than 30 cm. Also, a wiring distance from the resistor R1 to the diode D2 may be less than 10 cm. For example, as illustrated in
As to a position connected with the capacitor C1, it is better to be on a path between a connecting point Q of the resistor R1 and the diode D2 and an electrode of the plasma jet ignition plug 100 (the terminal fitting 40, etc.).
Further, electrostatic capacity of the capacitor C2 is set in order that a sum of energy at plasma formation, which is energy content supplied by stray capacitance or the capacitor C1 at trigger discharge, for a spark discharge gap, and energy content supplied from the capacitor C2, equals a supplied amount by performing one time plasma extrusion (e.g., 150 mJ). By this energy, plasma of a fire pillar shape (frame shape) can be extruded from the opening part 14, and an ignition of mixed gas by plasma can be performed.
While embodiments of the present invention has been described in detail and also in reference to a specific embodiment, it is clear to those skilled in the art that several modifications and changes can be without departing from the scope and spirit of the present invention.
This application is based on Japanese Patent Application 2009-035107 filed on Feb. 18, 2009, the content of which is hereby encompassed in reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| P.2009-035107 | Feb 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/052471 | 2/18/2010 | WO | 00 | 8/16/2011 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2010/095694 | 8/26/2010 | WO | A |
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