JP4682995B2 - Plasma ignition device and manufacturing method thereof - Google Patents

Description

  The present invention relates to measures against electrode consumption of a plasma ignition device used for ignition of an internal combustion engine.

In an internal combustion engine such as an automobile engine, in the plasma ignition device 1h as shown in FIG. 6A, a high voltage is applied from the discharge power source 20h between the center electrode 110h and the ground electrode 131h of the plasma ignition plug 10h. In addition, at the moment when discharge starts in the discharge space 140h formed between the center electrode and the installation electrode, a large current is supplied from the plasma generating power source 30h, and the gas in the discharge space 140h is heated to high temperature and pressure. It can be made into a plasma state and can be ignited by being injected from the tip of the discharge space 140h.
The plasma ignition device 1h is rich in directivity and can generate an extremely high temperature range of several thousand to several tens of thousands K in a large volume range, so that a lean air-fuel mixture is burned in the combustion of a direct injection engine. Therefore, it is expected to be applied to stratified combustion that facilitates combustion by collecting a rich air-fuel mixture in the vicinity of the spark plug.

As such a plasma ignition device, Patent Document 1 discloses that a center electrode and an insulator provided with an insertion hole extending vertically and holding the center electrode in the center are provided in order to prevent contamination of the center electrode. A surface gap type spark plug is disclosed which is constituted by a ground electrode provided with an opening communicating with the insertion hole at the lower end of the cover, and in which a discharge gap is formed in the insertion hole.
US Pat. No. 3,581,141

However, in the conventional plasma ignition device 1h, as shown in FIG. 6 (b), the center electrode 110h is a cathode and the ground electrode 131h is an anode, so that a cation 50 having a large mass on the surface of the center electrode 110h. Cathodic sputtering that is decomposed by the collision of the metal is likely to occur. Due to this cathode sputtering, the surface of the center electrode 110h is severely eroded.
Along with the erosion of the center electrode 110h, the distance between the center electrode 110h and the ground electrode 131h, that is, the discharge distance 141h gradually increases, and the discharge voltage gradually increases in proportion to the discharge distance 141h. If the generated voltage is exceeded, discharge may not be possible and the internal combustion engine may misfire.

  Therefore, in view of such circumstances, the present invention provides a plasma ignition device excellent in durability that suppresses the consumption of the cathode due to cathode sputtering in the plasma ignition device, hardly raises the discharge voltage, and realizes stable ignition. It is intended to provide.

According to a first aspect of the present invention, in the first aspect of the invention, a plasma ignition plug in which a cylindrical insulating member that insulates between the center electrode and the ground electrode is disposed to form a discharge space in the insulating member. A plasma ignition device that performs ignition by injecting gas in the discharge space into a high-temperature and high-pressure plasma state into an internal combustion engine by a high voltage applied between the center electrode and the ground electrode. An erosion-resistant layer is formed on at least one of the center electrode and the ground electrode that covers the surface of the electrode facing the discharge space, and the erosion-resistant layer is formed from the outermost layer. The layers constituting the layers leading to the innermost layer have different thermal properties and are composed of a plurality of layers in which these layers are laminated, and the outermost layer is a high boiling point layer having the highest boiling point,
The innermost layer is a high thermal conductivity layer having the highest thermal conductivity, and the layer between the outermost layer and the innermost layer has a higher thermal conductivity from the outermost layer side toward the innermost layer side, It is provided so that the boiling point becomes higher from the innermost layer side toward the outermost layer side.

When a high voltage is applied in the discharge space, the gas in the discharge space becomes a plasma state, and a cation having a large mass at a very high temperature collides with the surface of the electrode serving as the cathode, thereby eroding the electrode surface. Although there is a possibility of causing sputtering, according to the invention of claim 1, the outermost layer of the erosion-resistant layer formed on the electrode surface is a high boiling point layer, has a high boiling point, and a high temperature gas converted into plasma It is hard to evaporate even if it collides.
In addition, since the erosion resistant layer is formed in a layered form in combination with the high boiling point layer and the high thermal conductivity layer, the thermal energy of the plasma gas is quickly released from the high boiling point layer to the high thermal conductivity layer, Since the temperature of the boiling point layer can be lowered, the electrode surface is further difficult to evaporate, and cathode sputtering is suppressed.
Therefore, the durability of the plasma ignition device can be improved.

  According to a second aspect of the present invention, the erosion resistant layer is an inclined material formed so that the thermal properties gradually change in layers from the outermost layer to the innermost layer.

  According to the invention of claim 2, the outermost layer has the highest boiling point, the innermost layer has the highest thermal conductivity, and the gradient material in which the thermal properties of the outermost layer and the innermost layer gradually change. Therefore, the generation of internal stress due to the difference in material characteristics can be suppressed, and a plasma ignition device having excellent durability can be realized.

  In the invention of claim 3, the gradient material is composed of a high boiling point material and a high thermal conductivity material, and the blending ratio of the high thermal conductivity material is increased from the outermost layer side toward the innermost layer side, and The inclined material is formed by gradually changing the blending ratio of each layer so that the blending ratio of the high boiling point material increases from the inner layer side toward the outermost layer side.

According to the invention of claim 3, it becomes possible to easily form an inclined material in which the thermal properties are gradually changed by changing the blending ratio of the high boiling point material and the high thermal conductivity material. An integrated corrosion resistant layer can be formed.
Therefore, it is possible to realize a plasma ignition device having excellent erosion resistance.

  In the invention of claim 4, the high boiling point material is a high boiling point material containing at least one or more of metals or metal compounds having a boiling point of 3500 ° C. or higher.

  According to the invention of claim 4, a high-boiling layer hardly evaporates, cathode sputtering is suppressed, and a highly durable plasma ignition device can be realized.

  According to a fifth aspect of the present invention, the high thermal conductivity material is a high thermal conductivity material containing at least one or more of metals, metal compounds, or carbon fibers having a thermal conductivity of 100 W / m · K or more.

  According to the invention of claim 5, the temperature of the high melting point layer can be quickly lowered, further, cathode sputtering is suppressed, and a highly durable plasma ignition device can be realized.

  According to a sixth aspect of the present invention, in the method of manufacturing a plasma ignition device according to any one of the first to fifth aspects, the step of forming the electrode to be the cathode includes the high boiling point material and the high thermal conductivity material. And a high-boiling-point material from the innermost layer side toward the outermost layer side, the blending ratio of the high thermal conductivity material increases from the outermost layer side toward the innermost layer side. The composition ratio of each layer is gradually changed so as to increase the composition ratio, and the mixture is filled in the mold, and compressed by the mold to form a compact, and the compact is further compressed by the mold. At the same time, a pulse current is applied to the molded body through the molding die, and the molded body is sintered by the thermal energy generated in the molded body to form the electrode serving as the cathode together with the erosion resistant layer. Including process .

According to the invention of claim 5, for the high boiling point material and the high thermal conductivity material, regardless of whether it is a metal, a metal compound or a carbon fiber material, the blending ratio of both materials is changed from the outermost layer side to the innermost layer side. The composition ratio of the high heat conductivity material is increased toward the outermost layer, and the composition ratio of the high boiling point material is increased from the innermost layer side toward the outermost layer side. Becomes easy.
Therefore, a highly durable plasma ignition device can be realized.

Below, 1st Embodiment of this invention is described with reference to FIG.
The plasma ignition device 1 according to this embodiment includes a high-voltage power source including a discharge power source 20 and a plasma generation power source 30 and a plasma ignition plug 10.
The plasma-type spark plug 10 has an axial center electrode 110, a cylindrical insulating member 120 that insulates and holds the center electrode 110, and a bottomed cylindrical shape that covers the insulating member 120, and a ground electrode 131 is formed at the tip. And a conductive housing 130.
On the surface of the ground electrode 131 facing the discharge space 140, an erosion resistant layer 150 including a high boiling point layer 151, an inclined layer 152, and a high thermal conductivity layer 153, which will be described later, is formed.

  The insulating member 120 is made of high-purity alumina or the like excellent in heat resistance, mechanical strength, high-temperature dielectric strength, thermal conductivity, and the like, and a cylindrical discharge space 140 that extends downward from the tip surface of the center electrode 110 on the tip side. A center electrode locking portion that locks the housing 130 via a packing member that maintains the airtightness between the insulating member 120 and the housing 130 is formed in the middle, and the base electrode 120 and the housing 130 are disposed on the base end side. An insulating member head portion 122 is formed to prevent the high voltage from escaping other than the electrodes.

A distal end of the housing 130 covers the insulating member 120, and an annular ground electrode 131 that is bent toward the inside is formed.
An inner periphery of the housing 130 is fixed to the wall surface (engine block 40) of the internal combustion engine so that the ground electrode 131 is exposed in the internal combustion engine (not shown), and the housing 130 and the engine block 40 are electrically grounded. A housing screw part 133 is formed, and a housing hexagonal part 134 for fastening the screw part 133 is formed on the outer peripheral part on the base end side.

The ground electrode 131 is formed with a ground electrode opening 132 that communicates with the inner diameter of the insulating member 120 and faces the discharge space 140.
Furthermore, an erosion-resistant layer 150 is formed on the ground electrode 131 so as to cover the surface facing the discharge space 140.
The erosion-resistant layer 150 is formed as an inclined material formed so that the thermal properties gradually change in layers from the outermost layer to the innermost layer.
Specifically, a high-boiling layer 151 is formed using a high-boiling material as the outermost layer, and an inclined layer 152 is formed on the back side by gradually changing the blending ratio of the high-boiling material and the high thermal conductive material. Further, a high thermal conductivity layer 153 is formed on the back surface using a high thermal conductivity material to constitute an erosion resistant layer 150.

Further, the erosion resistant layer 150 is composed of a high boiling point constituent material having a high boiling point thermal property and a high thermal conductivity constituent member having a high thermal conductivity thermal property. The layers may be stacked in combination so as to be different.
Further, in the erosion resistant layer 150, the blending ratio is adjusted so that the thermal conductivity of the constituent material constituting the layer becomes higher toward the innermost layer from the outermost layer, and the innermost layer moves from the innermost layer to the innermost layer. You may provide as a gradient material which adjusted the mixture ratio so that the boiling point of the structural material which comprises the layer may become high as a layer.

As the high boiling point material, a high boiling point material containing at least one of metals or metal compounds having a boiling point of 3500 ° C. or higher is used.
Specifically, it is preferable to use a noble metal material such as Co as the metal, a carbide or nitride such as TaC, HfC, TiC, or TiN, or a material obtained by mixing and alloying them as the metal compound.
As the high thermal conductivity material, for example, a high thermal conductivity material containing either a metal having a thermal conductivity of 100 W / m · K or more, a metal compound, or carbon fiber is used.
Specifically, it is preferable to use Cu, Ag, Au or the like as the metal, metal carbides such as SiC or WC as the metal compound, and carbon nanotube (CNT), carbon nanofiber (CNF) or the like as the carbon fiber. .
In particular, carbon fibers such as CNT and CNF have an extremely high thermal conductivity of 1000 W / m · K to 3000 W / m · K, and are extremely excellent in heat dissipation.

The front end side of the center electrode 110 is formed of a high melting point material such as W, Ta, Mo, Hf, TaC, or TiN, and a center electrode central shaft 111 made of a highly conductive metal material such as a steel material is formed therein. Has been.
A central electrode terminal portion 112 that is exposed from the insulating member 120 and connected to the external discharge power supply 20 and the plasma generation power supply 30 is formed on the proximal end side of the central electrode 110.

In the first embodiment of the present invention, as shown in FIG. 2A, the polarities of the discharge power supply 20 and the plasma generation power supply 30 are set so that the center electrode 110 side becomes an anode and the ground electrode 131 side becomes a cathode. It is configured.
The discharge power source 20 includes a first battery 21, an ignition key 22, an ignition coil 23, an igniter 24 including a transistor, and an electronic control device 25, and is connected to the plasma ignition plug 10 via a rectifying element 26. The first battery 21 is grounded on the anode side.

  The plasma generating power source 30 includes a second battery 31, a resistor 32, and a plasma generating capacitor 33, and is connected to the plasma ignition plug 10 via a rectifying element 34. The second battery 31 is grounded on the cathode side.

When the ignition switch 22 is turned on and a negative primary voltage is applied from the first battery 21 to the primary coil 231 of the ignition coil 23 by the ignition signal from the ECU 25, and the primary voltage is cut off by switching of the igniter 24. The magnetic field in the ignition coil 23 changes, and a positive secondary voltage of 10 to 30 kV is induced in the secondary coil 232 of the ignition coil 23 by the self-induction action.
On the other hand, the plasma generating capacitor 33 is charged by the second battery 31.

When the applied secondary voltage exceeds a discharge voltage proportional to the discharge distance 141 between the center electrode 110 and the ground electrode 131, a discharge is started between both electrodes, and the gas in the discharge space 140 is plasma in a small region. It becomes a state.
The gas in the plasma state in this small region has conductivity and causes the discharge of the electric charge stored between the two electrodes of the plasma generating capacitor 33, thereby inducing further plasma state of the gas in the discharge space 140. To enlarge.
This expanded plasma state gas becomes high temperature and high pressure and is injected into the combustion chamber of the internal combustion engine.

At this time, as shown in FIG. 2A, the gas in the discharge space 140 becomes a high-temperature and high-pressure plasma state, and the cation 50 having a large mass collides with the surface of the opening 132 provided in the ground electrode 131. .
However, the anti-erosion layer 150 including the high boiling point layer 151, the inclined layer 152, and the high thermal conductivity layer 153 described above is formed on the surface facing the discharge space 140.
Therefore, even when the high-temperature cation 50 collides with the high boiling point layer 151, in addition to the high boiling point layer 151 having a high boiling point, the high thermal conductivity layer 153 quickly dissipates heat and is cooled. Erosion on the surface of the ground electrode opening 132 can be suppressed.

On the other hand, the cations 50 do not collide with the surface of the central electrode 110 serving as the anode because they are electrically repelled, and only the light electrons 51 collide, so that direct erosion due to cathode sputtering does not occur.
In addition, since the center electrode 110 is formed using a high melting point material, it is protected from indirect erosion due to radiant heat from a gas in a plasma state.

  In the present embodiment, the erosion resistant layer 150 may be formed by separately forming the high boiling point layer 151, the gradient layer 152, and the high thermal conductivity layer 153, and layering these layers. Using the material and powdery high thermal conductivity material, the blending ratio is adjusted so that the thermal conductivity of the constituent material constituting the layer becomes higher as the layer goes from the outermost layer to the innermost layer. In addition, the high boiling point layer 151 and the high thermal conductivity layer 153 are formed by the gradient material in which the blending ratio is adjusted so that the boiling point of the constituent material constituting the layer becomes higher toward the outermost layer from the innermost layer to the higher gradient layer. And can be formed as an integral electrode that continuously changes.

At this time, as shown in FIG. 3 (a), the blending ratio of the high boiling point material on the outermost layer facing the discharge space is set highest, and the blending ratio of the high boiling point material gradually decreases toward the innermost layer. The gradient blending is performed so that the blending ratio of the conductivity material is gradually increased.
In addition, the blending ratio of the high boiling point material and the high thermal conductivity layer of the high boiling point layer and the high thermal conductivity layer does not necessarily change linearly, as shown in FIG. Inclination may be blended so that changes.

By using the plasma sintering apparatus 50 as shown in FIG. 4, the erosion resistant layer 150 and the ground electrode 131 made of layers having different characteristics from the high boiling point layer 151, the gradient layer 152, and the high thermal conductivity layer 131 b are formed. A fully integrated electrode can be easily formed.
A manufacturing process for forming the ground electrode 131 serving as the cathode and the erosion-resistant layer 150 completely in the following will be described in detail.
The metal material used as the ground electrode 131 and the material having the high boiling point material and the high thermal conductivity material used as the erosion resistant layer 150 are powders, and the high boiling point layer 151, the inclined layer 152, and the high thermal conductivity are formed so as to cover the ground electrode 131. In order to form the layer 131c, the blending ratio of the high thermal conductivity material increases from the outermost layer side to the innermost layer side of the erosion resistant layer 150, and the blending ratio of the high boiling point material increases from the innermost layer side to the outermost layer side. The blending ratio of each layer is gradually changed so as to increase, and the molding die composed of the upper punch 54a, the lower punch 54b, the molding die 56, and the core pin 55 placed in the vacuum chamber 58 is filled. .

Next, the material blended in the molding allowance 56 is pressed by the pressurizing device 53 through the upper punch 54a and the lower punch 54b to obtain a molded body.
Further, while pressurizing the compact with the pressurizing device 53 and monitoring the temperature with the temperature monitoring device 57, the electric energy generated by the DC pulse power source 51 is supplied to the compact through the electrodes 52a and 52b.
As a result, extremely high-temperature heat energy is generated in the molded body, and the molded body is sintered. Thus, an electrode sintered body in which the erosion-resistant layer 150 and the ground electrode 131 are completely integrated is obtained.
The electrode thus formed and the housing 130 can be integrated by laser welding or the like.

In the second embodiment of the present invention, as shown in FIG. 5A, the polarities of the discharge power supply 20b and the plasma generation power supply 30b are configured such that the center electrode 110 side is a cathode and the ground electrode 131 side is an anode. To do.
In the present embodiment, the basic configuration is the same as that of the first embodiment, so common portions are denoted by the same reference numerals and description thereof is omitted.
In the present embodiment, as shown in FIG. 5B, the erosion resistant layer 150 is formed so as to cover the surface of the center electrode 110B facing the discharge space 140.
The erosion resistant layer 150 is formed as a gradient material formed so that the thermal properties gradually change in layers from the outermost layer to the innermost layer, and the high boiling point layer 151, the gradient layer 152, and the high thermal conductivity layer 153 are formed. Consists of.

With such a configuration, even when the cation 50 collides with the surface of the erosion resistant layer 150, the high boiling point layer 151 is formed on the outermost layer, and the high thermal conductivity is provided on the back side through the inclined layer 152. Since the layer 153 is formed, in addition to the high boiling point layer 151 being difficult to evaporate, the thermal energy of the cation 50 is quickly released to the high thermal conductivity layer 153, and the temperature of the high boiling point layer 151 quickly decreases. To do.
Accordingly, it is possible to suppress electrode consumption due to cathode sputtering as in the first embodiment of the present invention.
In this embodiment, in order to integrally form the erosion resistant layer 150 and the center electrode 150B, a manufacturing method using the above-described plasma sintering apparatus 50 can be applied.
At this time, since the center electrode 110B has a columnar shape, the core pin 55 used when forming the annular ground electrode 131 covered with the erosion-resistant layer 150 in the first embodiment is unnecessary.

As a matter of course, the present invention is not limited to the above embodiment, and can be appropriately changed without departing from the gist of the present invention.
For example, in the above-described embodiment, the erosion-resistant layer 150 is provided only on the electrode serving as the cathode. However, the anode is formed by laminating the high melting point layer and the high thermal conductivity layer in the same manner by the same manufacturing method as the erosion-resistant layer 150. If formed, the durability of the anode can be improved.
Therefore, further improvement in the durability of the plasma ignition device can be expected.

  In the above-described embodiment, the plasma ignition device including one plasma ignition plug has been described. However, the present invention can also be applied to a multi-cylinder engine including a large number of ignition plugs.

The block diagram which shows the plasma type ignition device in 1st Embodiment of this invention. (A) is a circuit diagram in a 1st embodiment of the present invention, and (b) is an important section sectional view showing an effect in this figure. The compounding characteristic of the gradient material which changed the compounding ratio of the high boiling point material and high heat conductivity material used for this invention is shown, (a) shows the example which changes linearly, (b) shows curve An example of change is shown. The block diagram which shows the outline | summary of the plasma sintering apparatus used for the process of integrally forming the electrode used as the cathode of this invention, and an erosion-resistant layer. (A) is a circuit diagram in a 2nd embodiment of the present invention, and (b) is an important section sectional view showing the effect in this figure. (A) is a block diagram which shows the conventional plasma type ignition device, (b) is principal part sectional drawing which shows the problem in this figure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Plasma type ignition device 10 Plasma type spark plug 110 Center electrode 120 Insulating member 131 Ground electrode 132 Ground electrode opening 140 Discharge space 150 Corrosion resistant layer 151 High boiling point layer 152 Inclined layer 153 High thermal conductivity layer 20 Discharge power source 30 Plasma generation Power supply 40 Engine block (internal combustion engine)

Claims (6)

A cylindrical insulating member that insulates between the center electrode and the ground electrode is disposed, and includes a plasma ignition plug in which a discharge space is formed in the insulating member,
In a plasma ignition device that performs ignition by injecting a gas in the discharge space into a high-temperature and high-pressure plasma state into an internal combustion engine by a high voltage applied between the center electrode and the ground electrode,
An erosion-resistant layer is formed on at least one of the center electrode and the ground electrode, which covers the surface of the electrode facing the discharge space.
The erosion-resistant layer is a layer having different thermal properties of the constituent materials constituting each layer from the outermost layer to the innermost layer, and is composed of a plurality of layers in which these layers are laminated,
The outermost layer is a high boiling point layer having the highest boiling point,
The innermost layer is a high thermal conductivity layer with the highest thermal conductivity,
The layer between the outermost layer and the innermost layer has a higher thermal conductivity from the outermost layer side toward the innermost layer side, and has a higher boiling point from the innermost layer side toward the outermost layer side. A plasma ignition device characterized in that the plasma ignition device is provided.   2. The plasma ignition according to claim 1, wherein the erosion-resistant layer is a gradient material formed such that thermal properties gradually change in layers from the outermost layer to the innermost layer. apparatus. The gradient material is composed of a high boiling point material and a high thermal conductivity material,
Increase the blending ratio of the high thermal conductivity material from the outermost layer side toward the innermost layer side, and increase the blending ratio of the high boiling point material from the innermost layer side toward the outermost layer side. 3. The plasma ignition device according to claim 2, wherein the gradient material is formed by gradually changing the blending ratio.   4. The plasma ignition device according to claim 3, wherein the high boiling point material is a high boiling point material containing at least one of metals or metal compounds having a boiling point of 3500 ° C. or higher.   4. The plasma according to claim 3, wherein the high thermal conductivity material is a high thermal conductivity material containing at least one of a metal, a metal compound, or carbon fiber having a thermal conductivity of 100 W / m · K or more. Type ignition device. In the manufacturing method of the plasma type ignition device according to any one of claims 1 to 5,
The step of forming the electrode to be the cathode comprises
Using a material in which the high boiling point material and the high thermal conductivity material are in powder form,
Each layer so that the blending ratio of the high thermal conductivity material increases from the outermost layer side toward the innermost layer side, and the blending ratio of the high boiling point material increases from the innermost layer side toward the outermost layer side. Fill the mold by gradually changing the blending ratio of
The molded body is compressed by the molding die, the molded body is further compressed by the molding die, and a pulse current is applied to the molded body through the molding die to generate heat generated in the molded body. Sinter the molded body with energy,
A method of manufacturing a plasma ignition device, comprising a step of forming an electrode to be the cathode together with the erosion resistant layer.