DE102006037038B4 - High frequency ignition device for high frequency plasma ignition - Google Patents

Abstract

High-frequency ignition device for a high-frequency plasma ignition, comprising a primary electrode (1) and a plurality of secondary electrodes (2), wherein the secondary electrodes (2) are electrically insulated from one another and from a collecting electrode (5) and capacitively connected to the collecting electrode (5) Capacitance (C) are connected, characterized in that the impedance of the capacitance (C) in the region of an excitation frequency of the plasma (6) is large compared to the impedance of the forming during the flashover plasma (6).

Description

The The present invention relates to a high-frequency ignition device for one High-frequency plasma ignition with the features of the preamble of claim 1.

to Ignition of inert fuel-air mixtures in internal combustion engines, in particular of lean or extremely rich mixtures as well as mixtures with a high proportion of exhaust gas or fuels that a high flash point (such as CNG compressed natural gas) must have a very high energy is introduced into the gas mixture and / or a larger mixture volume are inflamed when this z. As in stoichiometric gasoline-air mixtures necessary is.

A known Zündmöglichkeit that offers these features is the high-frequency plasma ignition, as shown for example in the DE 10 2004 058 925 is described. In this case, a resonant circuit or resonator, consisting of a coil inductively and a capacitor excited by a high-frequency source resonant until the capacitance representing electrodes ignites a high-frequency plasma flashover. The design used so far is based on the conventional spark plug, ie it consists of an external ground electrode connected to the screwed connection and an insulated central rod electrode. The coupling of higher energy at the same boundary conditions leads to a greatly increased electrode wear. A consequent shorter service life compared to conventional ignition systems is disadvantageous for series production, especially in motor vehicles.

at Conventionally operated ignition systems could by combining high melting point materials and materials with good thermal conductivity the life of the spark plug electrodes Values of more than 1000 operating hours can be improved. In the RF plasma ignition in the form known in the prior art are those with However, these materials reached a long service life, so that optimization of electrode materials is not sufficient increase the lifetime promises.

One Main reason for the spark plug electrode wear is the Material removal by a thermal overload of the electrode material at the bottom of the plasma flashover.

One known way of reducing the point load on the electrodes is to divide the plasma flashover into two or more plasma flashovers. By dividing the plasma flashover into several channels, the energies in the individual plasma flashovers and thus the thermal load of the individual foot points decrease. Such a division of a spark on a plurality of ground electrodes is for conventional spark plugs z. B. from the DE 696 06 686 T2 known.

Furthermore, from the DE 25 41 937 A1 discloses a method and apparatus for igniting a fuel-air mixture. In particular, a corona electrode for enriching fuel droplets is shown. A corresponding ignition should lead to an arc discharge. Such an ignition system is associated with a distribution of the corresponding ignitable mixture to the entire system of the electrode or the electrodes. Overall, the illustration refers to discharge devices of a general nature. A plasma discharge is not addressed.

In the DE 38 78 336 T2 a spark plug is described, which is to learn by means of auxiliary electrodes, a lighter ignition. In this case, an auxiliary spark gap is formed, at which a first capacitive discharge is caused.

there is for the auxiliary spark gap requires a lower voltage than for a normal one Radio link. A plasma ignition is not disclosed in this document.

adversely in such known in the art spark plugs is that a plasma flashover Only bad and uneven on several Plasma arcing divides. A plasma can be described primarily as a highly nonlinear resistor become. Therefore, usually only one conductive channel is formed, there in an ignited Plasma rollover a lower resistance than in the corresponding air gap.

It is therefore an object of the present invention, an ignition device for one High-frequency plasma ignition indicate that the electrode load is significantly reduced.

These Task is by an igniter solved with the features of claim 1. Advantageous developments are in the subclaims specified.

Advantageously, in a spark plug according to the invention by the capacitive coupling via the capacitance C, a current divider with complex resistors for the high-frequency Anregegungswechselstrom the high-frequency plasma ignition formed and unlike a purely resistive current divider, the currents are proportional to the complex resistors on the multiple secondary electrodes. As soon as a plasma flashover forms, it does not already create a current path through it with very low resistance to the other options.

In better embodiment is the impedance of the capacitance C in the frequency range of the plasma large compared to the impedance of the flashover forming plasma.

By properly sized capacities C, with which the secondary electrodes coupled to the collecting electrode, it is possible to increase the impedance of the capacitance C in the region high opposite the excitation frequency the impedance of the plasma flashover to keep. The impedance of the capacitance C is then dominant over the of the ignited Plasmas and thus will be the impedance of the system, plasma channel and capacity C for coupling, linearized and forms a complex flow divider, the easy and reliable Way leads to multiple plasma flashovers.

In advantageous embodiment is the primary electrode in the center, d. H. arranged in the symmetry axis of the ignition device.

The central arrangement allows starting from the middle of several rollover routes to the edge of the ignition device out.

In better embodiment can the multiple secondary electrodes segments separated by slots arranged around the center electrode Secondary electrode cylinder be, each having a capacity C with another the secondary electrode cylinder form surrounding collecting electrode cylinder as collecting electrode.

The Segmentation of the secondary electrode in two or more parts, each of which with the collecting electrode through a capacity C is coupled a simple structure, because the opposite surfaces of the Secondary electrode cylinder and the collecting electrode cylinder already assigned to each capacity C form.

Of the Collecting electrode cylinder can with the mass of the igniter be connected.

The secondary electrodes can with the collecting electrode outside the ignition device be connected capacitively.

It is also possible connections from the ignition device to lead out and the capacities C completely or partly outside the ignition device to arrange.

The The present invention will be described below by means of an embodiment with the attached Drawing closer explained. It shows

1 schematically the electrode assembly of a spark plug according to the invention.

1 shows schematically the electrode assembly of a spark plug according to the invention. A primary electrode 1 is arranged centrally in the axis of the ignition device according to the invention in this schematic view. Three secondary electrodes 2 here consist of segments separated by slots concentric with the primary electrode 1 arranged secondary electrode cylinder 3 , Another concentric to the primary electrode 1 and outside the secondary electrode cylinder 3 arranged collecting electrode cylinder 4 serves as a collecting electrode 5 and is connected to the ground in the present embodiment. The secondary electrodes 2 form with the concentric and spaced collecting electrode 5 each a capacity C, as indicated by the symbols in the drawing.

By properly dimensioned capacitances C, with which the secondary electrodes 2 to the collecting electrode 5 coupled, it is possible, the impedance of the capacitance C in the region of the excitation frequency high compared to the impedance of one between the primary electrode 1 and the secondary electrode 2 forming plasma flashover 6 to keep. The impedances of the capacitances C are then dominant over that of the ignited plasma flashover 6 and form a current divider with complex resistances, which in a simple and reliable way to several plasma flashovers 6 leads.

As a result, a long service life of the electrodes can be achieved because a selective thermal overload of the primary electrode 1 and the secondary electrodes 2 is avoided. Through a spatial distribution to several plasma flashovers 6 a more even and thus faster heating of the air in the ignition of the ignition device is possible. With the same service life is the use of cheaper or better to process materials for primary electrode 1 and / or secondary electrodes 2 conceivable.

By the choice of different capacities C for the individual secondary electrodes is also an adaptation to non-symmetrical geometry ratios possible.

1

primary electrode

2

secondary electrode

3

Secondary electrode cylinder

4

Collecting electrode cylinder

5

collecting electrode

6

Plasma rollover

C

capacity

Claims (6)

High-frequency ignition device for a high-frequency plasma ignition, having a primary electrode ( 1 ) and a plurality of secondary electrodes ( 2 ), the secondary electrodes ( 2 ) with each other and with respect to a collecting electrode ( 5 ) are electrically isolated and with the collecting electrode ( 5 ) are capacitively connected via a capacitance (C), characterized in that the impedance of the capacitance (C) in the region of an excitation frequency of the plasma ( 6 ) is large compared to the impedance of the plasma forming during the flashover ( 6 ). Ignition device according to claim 1, characterized in that the primary electrode ( 1 ) is arranged in the center, ie in the symmetry axis of the ignition device. Ignition device according to claim 2, characterized in that the plurality of secondary electrodes ( 2 ) segments separated by slots around the primary electrode ( 1 ) arranged secondary electrode cylinder ( 3 ), each having a capacity (C) with another, the secondary electrode cylinder ( 3 ), collecting electrode cylinders ( 4 ) as a collecting electrode ( 5 ) form. Ignition device according to claim 3, characterized in that the collecting electrode cylinder ( 4 ) is connected to the mass of the ignition device. detonator according to one of the preceding claims, characterized that the secondary electrodes with the collecting electrode outside the ignition device capacitively connected. Method for generating plasma flashovers in a high frequency plasma ignition device having a primary electrode ( 1 ) and a plurality of secondary electrodes ( 2 ) for the multiple formation of plasma peaks, characterized in that - the secondary electrodes ( 2 ) with each other and with respect to a collecting electrode ( 5 ) are electrically isolated and with the collecting electrode ( 5 ) are each connected capacitively via a capacitor (C) and - the capacitances (C) with which the secondary electrodes ( 2 ) to the collecting electrode ( 5 ) are designed such that the impedance of the capacitance (C) in the region of an excitation frequency is high compared to the impedance of the plasma forming during the flashover (FIG. 6 ), so that the impedance of the capacitance (C) is dominant over that of the ignited plasma.