DE2739413A1 - SPARK PLUG - Google Patents

Description

Dnimler-Benz Aktiengesellschaft Daitn 11

Stuttgart August 31, 1977

¹¹ spark plug "

The invention relates to a spark plug for internal combustion engines.

Fuel-air mixtures in gasoline engines are generally used by means of a spark discharge between the electrodes of a spark plug at an optimal point in time for engine operation inflamed. This spark discharge is fed by a high-voltage pulse from a suitable ignition system. Conventional Ignition systems and spark plugs with electrode spacings between 0.7 and 1.5 now ignite fuel-air mixtures with stoichiometric mixing ratio (air ratio \ * l) or a small excess of fuel ("rich" area, λ ^ l) problem-free.

Now the working range for minimal emission of harmful exhaust gases (CO ₁ NO, CH) and for low specific fuel consumption is not in the range of greatest IN safety, but in the so-called "lean" range (air ratio λ> 1). The operation of the engine in this inherently advantageous range requires increased ignition reliability in order to avoid misfires.

In practice, inhomogeneities in the mixture cannot be ruled out.

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ßen, βο that at times in the area of the hot spark piaemas no an ignitable mixture is present, which causes inflammation may occur. The likelihood of such phenomena increases as the fuel-air mixture becomes lean. In this case, it is obvious and customary to use the initial volume that is essential for the ignition process, the generated by the ignition spark. This is generally done by the distance between the electrodes (length of the Spark) and / or provided per spark event « Energy can be increased. For practical reasons, there is a limit (1.5 mm) to the increase in the distance between the electrodes. because the ignition voltage requirement is too high to cope with the conventional technology in the engine area can be mastered without any problems. The energy to be supplied to the spark is im generally increased by lengthening the burning time of the spark, so that due to the possibly very violent movement of the charge the probability is increased in the combustion chamber, while the "burning" spark "an ignitable mixture in its effective range respectively.

In the timing of the spark, different Recognize stages. If there are no subtleties, a distinction is made between "spark head" and "spark tail".

The spark head is the phase of the spark breakdown, in which the capacitances in the vicinity of the electrode discharge. The spark tail consists of a transition phase and the subsequent glow discharge.

The discharge currents in the spark head are relatively high (anipere area) and peak values can be up to several depending on the arrangement

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1OO A. Because especially in the beginning phase of the breakthroughs If the spark voltage is still very high, the plasma is supplied with high amounts of energy, which are primarily in the form of potential energy (dissociation, excitation and ionization in multiple stages) is stored and later the expanding Spark channel feeds. In contrast, the spark plasma becomes energy in the later stages of the discharge (glow phase) fed in a more uneconomic way, as loss processes increase and above all about half of the electrically supplied power drops at the electrodes and is dissipated there in the form of heat which is thus lost to the plasma. The initial volume generated by a "normal" spark head is in Expansion and temperature for a successful ignition sufficient. With times of the order of magnitude of approximately 10 μs, this initial volume is clearly of the electrically generated volume hot plasma volume can be distinguished, provided that an ignitable mixture is present in the area of the plasma volume during this time was. An increased energy supply in the initial phase (enlargement of the spark head) increases the initial volume of the Spark plasma and influences the subsequent ignition, so that the probability of ignition increases to the same extent how the activated volume that has arisen up to the onset of the exothermic reaction has increased.

Now, as a result of the movement of the charge in the engine compartment, flow velocities can occur occur, the ζ.Π. Only after 1 ms do the ignitable mixture enter the electrode area again. Therefore it can be advantageous if the spark tail continues at least in the form of a glow discharge in order to activate an Maintain plasma volume. If one generates with conventional

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nellen ignition systems a reinforced point head through redistribution the energy stored in the ignition system and thus given, may be due to the shortened energy supply (Spark duration) the profit can be nullified again because longer-lasting ignition conditions would be required. Ignition systems with which several spark heads can be generated one after the other are then of great advantage. the number and the repetition frequency can possibly be adapted to the motor conditions. The technical The prerequisites for this are met by modern semiconductor electronics, so that solutions are also tolerable in practice Effort can be realized.

Since, as already mentioned above, a short spark head with times around 10 us also has a volume with a diameter of mm range and can generate sufficiently high temperatures, it is desirable to keep the spark head as short as possible to design.

It is therefore the object of the invention to redesign the known design of conventional spark plugs so that an ignition spark can be generated with a short spark head and the smallest possible spark or no spark tail.

This object is achieved in that at least one spark gap is provided and each spark gap is coupled to the ignition voltage source with a large impedance.

Further details can be found in the following description and drawing of an exemplary embodiment. It deals a spark plug with three spark gaps.

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In the drawing show: Fig. 1 is a basic circuit diagram and

Fig. 2 shows a spark plug in plan and section.

The basic circuit diagram of Fig. 1 shows three capacitive to the ignition voltage source U coupled spark gaps. The capacitances 1 shown in dashed lines are the electrode capacitances and the capacities labeled 2 represent the coupling capacities, the coupling capacitance should be greater than the electrode capacity.

Fig. 2 shows a spark plug according to the invention in plan and in section. The outer shape of the metallic housing 3 of the spark plug is adapted to the dimensions of conventional spark plugs. A number of counter-electrodes k corresponding to the number of spark gaps in the spark plug are attached to the end of the screw-in thread 5 in the usual manner. The electrodes 6 opposing them are fitted in the plug insulator 7, electrically insulated from one another. In the upper part of the insulator, they each form the inner conductor of a coaxial capacitor 2, which is separated from the outer electrodes 9 by a dielectric 8. The outer electrodes 9 are connected to a common connection 10, which represents the feed to the ignition system in a known Veise.

Of course, it is also conceivable to separate the coupling capacitances from the spark plug in a plug

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plug to mount and the multi-spark spark plug with a to contact the appropriate multi-pole high-voltage plug. In this case, the part of the spark plug protruding into the combustion chamber remains unchanged from that in FIG. Only the upper part of the plug insulator is designed in such a way that a multi-pole plug connection to the plug connector arises. The upper end of each electrode is designed as a plug contact. The switching elements for decoupling the individual spark gaps on the one hand and for coupling to the ignition system on the other hand then contains the spark plug connector. This arrangement offers the advantage over that shown in FIG. 2 that the switching elements can be varied more widely given is.

Instead of a capacitor, the coupling impedance can also be a voltage-dependent resistor - VDR.

The investigations with spark plugs designed in this way in the laboratory * have shown that in the case of the supply, for example, with a conventional coil ignition, the ignition sparks at each pair of electrodes consist of spark head-like ones that follow one another in time Discharges exist, their mechanism of origin is similar to that of the known tilting oscillations. The total duration of a spark event is of course versus that shortened with a conventional spark plug. But now it is easily possible to determine the number of successive spark heads to be influenced in a targeted manner, as has already been mentioned above in the description. The duration of the spark event can thus be adapted to changing engine conditions.

The advantages of the ignition device explained in the description

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with capacitive coupling (high impedance, i.e. relatively small capacitance) can be summarized as follows:

1. Short spark heads are created that enable effective energy transfer to allow the spark plasma.

2. With an arbitrarily selectable (programmable) duration of the spark process (serial multiple sparks), the entire Power consumption of the system within limits.

3. There can be several geometrically spaced spark gaps are ignited at the same time (parallel multiple sparks).

In this way, several initial volumes can be activated at the same time, so that the ignition reliability is increased accordingly and "leaner" mixtures are ignited more reliably.

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Claims (6)

Daimler-Benz Aktiengesellschaft Daim 11 651 / fr Stuttgart 3I.8.77 "Spark plug" Claims Spark plug for internal combustion engines, characterized in that at least one spark gap ( k , 6) is provided and each spark gap is coupled to the ignition voltage source with a high impedance. 2. Spark plug according to claim 1, characterized in that the impedance is a capacitor. 3 · Spark plug according to claim 2, characterized in that the Capacitor is designed as a cylinder capacitor. k. Spark plug according to Claim 3, characterized in that the capacitor is designed as a coaxial capacitor (6, 9), the inner conductor (6) of which forms the one electrode, the outer conductor of which is connected to the ignition cable connection (10) and its dielectric (8) of the ceramic Material of the insulator (7) is formed. 5 «Spark plug according to Claim 1, 2 or 3, characterized in that that the impedance is arranged in the spark plug connector. 909810/0377 ORfGINAL! - 2 - daim 11 6. Spark plug according to claim 1, 2 or 3i, characterized in that that the impedance is a voltage-dependent resistance element - VDR - with a suitably selected breakdown voltage. 909810/0377