JP2017075591A - Ignition device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve ignition stability of an ignition plug using microwaves in an ignition device.SOLUTION: An ignition device comprises: a discharge section; a radiation section which radiates an electromagnetic wave to a space; an ignition plug provided with transmission means transmitting the electromagnetic wave to the radiation section; a detection section which detects a reflected wave from a reflection section; and a control section which controls amplitude of the electromagnetic wave supplied to the transmission means according to the amplitude of the reflected wave detected by the detection section. When the amplitude of the reflected wave detected by the detection section is larger than a predetermined value, the control section estimates that the space has too much plasma density and reduces power of the electromagnetic wave supplied to the transmission means.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a spark plug to which a high voltage pulse for spark discharge and an electromagnetic wave supplied as energy to the spark discharge are fed, and an ignition device including a control device for controlling the spark plug.

  2. Description of the Related Art Conventionally, an ignition plug has been developed in which local plasma is generated by using discharge of an ignition plug and the plasma is expanded by electromagnetic waves such as microwaves (for example, Patent Document 1 by the present applicant). In the spark plug disclosed in Patent Document 1, a high voltage pulse for spark discharge and microwave energy from a microwave oscillator are input to the spark plug. Then, a high voltage pulse for spark discharge is guided to the discharge electrode of the spark plug through the inside of the center electrode, and spark discharge is generated between the ground electrode. On the other hand, the microwave is guided to the tip of the spark plug through the outer surface of the center electrode, and the microwave is radiated from this tip. According to this spark plug, plasma is generated by spark discharge first, and then the microwave is radiated for a certain period, so that the plasma can be sustained for a certain period. This makes it possible to increase the combustion efficiency.

JP 2009-036198 A

  However, in the spark plug of Patent Document 1, when the microwave is emitted after the plasma is generated by spark discharge, if the density of the generated plasma is too high, the microwave is reflected by the plasma, and the reflected wave passes through the spark plug. The ignition (ignition) property may not be stable for reasons such as backflowing back to the microwave oscillator or interfering with the traveling wave of the microwave. Therefore, it is originally preferable to grasp the microwave irradiation conditions so that the microwaves are not reflected, and to set the magnitude and phase of the microwave supplied from the microwave oscillator to the ignition plug according to the conditions.

  However, the magnitude of the plasma density of the plasma actually generated in the combustion chamber varies depending on the pressure in the combustion chamber, the rotational speed, the flow of the air-fuel mixture, and the like. Therefore, it may be difficult to fix the microwave condition supplied to the spark plug to a preset value.

  The present invention has been made in view of the above points.

  The ignition device of the present invention includes a discharge unit, a radiating unit that radiates electromagnetic waves to space, a spark plug that includes a transmission means that transmits electromagnetic waves to the radiating unit, a detection unit that detects reflected waves from the radiating unit, A control unit is provided for controlling the magnitude of the electromagnetic wave supplied to the transmission means according to the magnitude of the reflected wave detected by the detection unit. In this case, the plasma density in the space is estimated to be excessive, and the power of the electromagnetic wave supplied to the transmission means is reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the stability of the ignition by the spark plug using a microwave can be improved.

1 is a schematic block diagram of an ignition device according to an embodiment of the present invention. The front view of the partial cross section of the spark plug which concerns on one Embodiment of this invention. The figure which shows the front-end | tip part of the said ignition plug.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the following embodiment is a preferable illustration, Comprising: It does not intend restrict | limiting the range of this invention, its application thing, or its use.

  Referring to FIG. 1, the ignition device of the present embodiment includes a control device 100, a high voltage pulse generator 150, a microwave generator 200, a mixer 300, and a spark plug 400. The spark plug 400 is a spark plug for creating a local plasma using spark discharge and expanding / maintaining this plasma with microwaves, and its configuration and structure will be described later.

  The high voltage pulse generator 150 includes an ignition coil that generates a high voltage pulse for spark discharge, and the high voltage pulse is input to the mixer 300.

  The microwave generator 200 is for generating the above-described microwave, and the generated microwave is input to the mixer 300. The microwave generator 200 includes a pulse generator 210, an amplifier 220, and a detector 230. The pulse generator 210 oscillates a microwave of about 2.5 GHz based on a command from the control device 100 and generates a microwave having a specified duty ratio or pulse pattern. The amplifier 220 amplifies the amplitude of the microwave generated by the pulse generator 210 to an appropriate value based on a command from the control device 100. The detector 230 receives a reflected wave from the spark plug 400 that passes through the mixer 300. The detector 230 detects the magnitude of the reflected wave and outputs it to the control device 100.

  Although not shown in FIG. 1, a directional coupler composed of a circulator or the like is provided at the output section of the microwave generator 200. Basically, the output (progression) from the amplifier 220 is provided. Wave) is output only to the mixer 300 side, and the output (reflected wave) from the mixer 300 is output only to the detector 230 side.

  The mixer 300 mixes the high voltage pulse from the high voltage pulse generator 150 and the microwave from the microwave generator 200 and outputs the mixed result to the spark plug 400. Referring to FIG. 2, the mixer 300 includes a microwave input terminal 310, a pulse input terminal 315, a mixed output terminal 340, a rod-shaped conductive member 320, an inner cylindrical conductive member 321, an outer cylindrical conductive member 330, and the like.

  The microwave from the microwave generator 200 is input to the microwave input terminal 310. The high voltage pulse from the high voltage pulse generator 150 is input to the pulse input terminal 315. A high voltage pulse and a microwave are output from the mixed output terminal 340 to the spark plug 400.

  The rod-shaped conductive member 320 has one end electrically connected to the pulse input terminal 315 and the other end electrically connected to the inner conductor 340a of the mixed output terminal.

  The inner cylindrical conductive member 321 surrounds the rod-shaped conductive member 320 with a space therebetween, is arranged coaxially with the rod-shaped conductive member 320, and is electrically connected to the inner conductor 310a of the microwave input terminal 310.

  The outer cylindrical conductive member 330 accommodates the inner cylindrical conductive member 321 and the like at an interval from the inner cylindrical conductive member 321 and is arranged coaxially with the inner cylindrical conductive member 321 and the like. The outer cylindrical conductive member 330 is electrically connected to the outer conductor 310b of the microwave input terminal 310 and the outer conductor 340b of the mixed output terminal 340, respectively.

  The microwave supplied from the microwave input terminal 310 configures a gap 322 between the inner cylindrical conductive member 321 and the outer cylindrical conductive member 330 as a resonator parallel to the axis (longitudinal direction). Further, the inner cylindrical conductive member 321 and the rod-shaped conductive member 320 are joined by capacitive coupling so that the microwave is supplied to the spark plug 400 via the rod-shaped conductive member 320.

  2 and 3, the spark plug 400 includes a center electrode 450, an insulator 480, a metal shell 470, a ground electrode 460, and a discharge part 490. The center electrode 450 is a cylindrical conductor, and transmits a high voltage pulse through its inner 450a, while transmitting microwaves through its outer surface 450b.

  The insulator 480 is a cylindrical insulator (for example, formed of ceramic), and has a shaft hole into which the center electrode 450 is fitted. The metal shell 470 is formed of a cylindrical metal conductor formed so as to surround the insulator 480. On the outer peripheral portion of the metal shell 470, a female screw portion (not shown) that is screwed into a spark plug mounting hole of a cylinder head of the internal combustion engine is provided. The discharge part 490 is an electrode part joined to the tip of the center electrode 450 and made of iridium or an iridium alloy in which tantalum or the like is mixed. One end of the ground electrode 460 is joined to the tip of the metal shell 470, and the other end faces the discharge part 490.

  When the high voltage pulse is transmitted from the center electrode 450 to the discharge unit 490, a spark discharge is generated due to a potential difference generated between the discharge unit 490 and the ground electrode 460. Further, the microwave transmitted through the outer surface 450 b of the center electrode 450 is radiated from the outer peripheral tip 450 c of the center electrode 450. As a result, it is possible to generate plasma at the tip of the spark plug 400.

  Here, originally, it is preferable that the plasma is further expanded / maintained by irradiating the plasma generated by spark discharge or the like with microwaves. However, when the plasma density of the plasma generated in the space near the tip of the spark plug 400 is too large, the microwave is reflected without being absorbed by the plasma even if the microwave is irradiated to the space. As a result, there is a disadvantage that the microwave flows back through the spark plug 400 and returns to the microwave oscillator 200 through the mixer 300. Conversely, if the plasma density of the plasma generated in the space is too small, the ignition (ignition) performance will be low. Therefore, the plasma density of the plasma generated in the space is preferably set to an intermediate value, that is, a size that does not reflect microwaves and can ensure ignition performance.

Therefore, the control device 100 of the ignition device of the present invention performs the following control as an example.
(1) First, control is performed to radiate microwaves from the radiation unit 490 so as to synchronize with the spark discharge from the discharge unit 490 or at a slightly later timing.
(2) In (1) above, the microwave output is usually set to a high level in order to perform reliable ignition, while the plasma density in the space is very high immediately after the spark discharge. Therefore, the microwave irradiated to the space is reflected by the plasma.
(3) As a result, when the detector 230 detects the reflected wave, the magnitude is digitized and output to the control device 100.
(4) In response to this, the control device 100 controls the amplifier 220 to lower the amplitude of the microwave by lowering the gain. Alternatively, the power of the microwave may be lowered by controlling the pulse generator 210 and lowering the duty ratio.
(5) The operations of (3) and (4) above are performed until the reflected wave becomes zero or until a preset value is reached, or the reflected wave detected at the first time of (3) is about 10%, for example. Repeat until it is.

In addition, it is assumed that said (1)-(5) is implemented at the following timings.
(A) When this ignition device is mounted on a new engine. For example, in the stage before shipment of the engine, the tests according to the above (1) to (5) are performed under a plurality of rotational speed and load conditions, and an appropriate microwave size and duty are set for each condition. Make a decision.
(A) After shipping the engine (automobile), the above (1) to (5) are adaptively performed during actual travel. For example, when the current rotation speed is 2000 rpm and when it becomes 2500 rpm according to the driver's instruction (further depression of the accelerator), the power of the microwave is first changed based on the prediction, and the reflected wave is temporarily large. If too much, the above operations (1) to (5) (particularly the above (4) and (5)) are performed.
(C) Since the plasma density is considered to vary depending on the outside air temperature (season and time zone such as day / night), the operations (1) to (5) are performed immediately after the start of driving of the automobile.

  The embodiment of the present invention has been described above. The scope of the present invention is determined based on the invention described in the claims, and should not be limited to the above embodiment.

For example, although microwaves have been described as an example of electromagnetic waves, electromagnetic waves in other wavelength ranges may be used.
Further, the internal combustion engine to which the present ignition device is applied is assumed to be a reciprocating gasoline engine or a rotary gasoline engine for automobiles, but may be applied to, for example, an engine using natural gas as fuel or an engine using light oil as fuel. .
In addition, the present invention is not limited to an ignition device, and may be applied to an electric device such as a microwave oven as a plasma device. In the above description, the outer surface 450b of the center electrode 450 is taken as an example of transmission means for transmitting electromagnetic waves to the radiating portion. However, the electromagnetic waves may be transmitted using a dedicated transmission line different from the center electrode 450. Good.

DESCRIPTION OF SYMBOLS 100 Controller 150 High voltage pulse generator 200 Microwave generator 210 Pulse generator 220 Amplifier 230 Detector 300 Mixer 400 Spark plug 450 Center electrode 460 Ground electrode 470 Main metal fitting

Claims (2)

A spark plug including a discharge unit, a radiating unit that radiates electromagnetic waves to space, and a transmission means that transmits electromagnetic waves to the radiating unit;
A detection unit for detecting a reflected wave from the radiation unit;
A control unit for controlling the magnitude of the electromagnetic wave supplied to the transmission means according to the magnitude of the reflected wave detected by the detection unit,
The control unit estimates that the plasma density in the space is excessive when the magnitude of the reflected wave detected by the detection unit is larger than a predetermined value, and reduces the magnitude of the electromagnetic wave supplied to the transmission unit. Ignition device. A radiation part that radiates electromagnetic waves into space;
A detection unit for detecting a reflected wave from the radiation unit;
A control unit for controlling the magnitude of the electromagnetic wave supplied to the transmission means according to the magnitude of the reflected wave detected by the detection unit,
The control unit estimates that the plasma density in the space is excessive when the magnitude of the reflected wave detected by the detection unit is larger than a predetermined value, and reduces the magnitude of the electromagnetic wave supplied to the transmission unit. Plasma equipment.