EP1979608B1 - Arrangement for detecting a measuring signal on a high voltage side, in particular a signal corresponding to ion current between sparking plug electrodes of an internal combustion engine - Google Patents

Description

The invention relates to an arrangement for high-voltage side detection of a broadband measurement signal, in particular a signal corresponding to the ion current between the electrodes of a spark plug of an internal combustion engine. The arrangement has at least one first current path, in which at least the secondary winding of the ignition transformer is arranged, and a second current path, in which at least the spark gap formed by at least two electrodes of a spark plug is arranged.

The combustion process of a gasoline-air mixture in internal combustion engines, especially in gasoline engine engines, is initiated by a spark generated by a high voltage applied between two electrodes of a spark plug. When reaching a breakdown voltage is between the Electrodes generated as a result of an arc discharge an arc, which is also referred to as a spark. By the arc discharge, by the resulting during the discharge of UV radiation and by the combustion process of the gasoline-air mixture, a chemical and thermal ionization, and it will be generated in the combustion chamber charge carriers, which even after the arc in the area between the electrodes Spark plug are available. The number and distribution of these charge carriers is particularly dependent on the internal pressure in the cylinder and the combustion process itself.

In the combustion process, a thermal-chemical chain reaction is initiated, in which so-called radicals are formed in addition to the ions. In chemistry, radicals are atoms and molecules with at least one unpaired electron, which usually have a high reactivity. Due to this reactivity, radicals usually only exist for a very short time. By a voltage applied to the electrodes of the spark plug, the reaction sequence can be measured as a current flow. This reaction process is very fast. As a result, the ion current generated between the electrodes contains high frequency components. In order to obtain the most informative information possible about the combustion process, a broadband measurement signal must be determined. In known measuring arrangements, the evaluation circuit is arranged in series with the secondary coil, whereby the secondary coil acts as a low-pass filter. As a result, not all frequency components of the ionic current can be determined and evaluated. Furthermore, in known systems, the measurement circuit affects the available spark energy.

From the document WO 97/22803 A2 an arrangement for high-voltage side detection of the broadband measurement signal with three parallel current paths is known. In the first current path, the secondary winding of an ignition transformer and in the second current path, the spark gaps formed by at least two electrodes of the spark plug is arranged. In the third current path a measuring resistor is arranged.

The object of the invention is to provide an arrangement in which a broadband measurement signal determined in a simple manner high voltage side and at the energy available for generating the arc is not or only slightly reduced.

This object is achieved by an arrangement for high-voltage side detection of a broadband measurement signal having the features of patent claim 1. Advantageous developments of the invention are specified in the dependent claims.

The arrangement with the features of claim 1 ensures that the electrodes of the spark plug, a relatively large amount of energy for generating the arc can be supplied while measuring ion currents and other high-frequency signal components precise high-voltage side. An irregular fuel combustion in internal combustion engines, which is also referred to as knocking, can be reliably detected by this arrangement in the entire speed-load range of an internal combustion engine, since the available measurement bandwidth is certainly greater than the acoustic resonance frequency of the combustion chamber. As a result, even when using the high-voltage side measuring circuit in the entire speed-load range, sufficient energy is available for initiating safe combustion.

If the measuring voltage is provided, for example, by means of a capacitor which is charged by the high voltage generated by means of the ignition transformer, only relatively little energy is withdrawn for generating the measuring voltage. The decoupling of the measuring circuit from the secondary coil preferably uses a diode which is present in known circuit arrangements and serves there to suppress the switch-on pulse. In the suppression of the switch-on pulse, a secondary-side high voltage is prevented as a result of the primary-side connection of the supply voltage.

A second aspect of the invention relates to a further arrangement for high-voltage side detection of a broadband measurement signal, in particular a signal corresponding to the ion current between the electrodes of a spark plug of an internal combustion engine. The arrangement has three parallel current paths, wherein at least the secondary winding of an ignition transformer and in the second current path at least the spark gap formed by at least two electrodes of the spark plug are arranged in the first current path. In the third current path at least one measuring resistor is arranged. At least in a range between the connection of the secondary winding and the measuring resistor is used at least a portion of a transformer core of the ignition transformer as an electrical conductor.

By this arrangement it is achieved that a broadband measurement signal can be determined without the energy provided by the secondary coil of the Zündtransformators for generating an arc with the aid of the spark plug is not or only slightly reduced by the measuring circuit, a space-saving arrangement of the elements in particular it is possible that the transformer core is used as an electrical conductor.

Fig. 1

einen Stromlaufplan einer bekannten Schaltungsanordnung zum Erfassen eines Ionenstroms zwischen den Elektroden einer Zündkerze einer Brennkraftmaschine;

Fig. 2

den Stromlaufplan einer Schaltungsanordnung zum Erfassen eines breitbandigen Messsignals gemäß einer ersten Ausführungsform der Erfindung;

Fig. 3

einen Stromlaufplan einer Schaltungsanordnung zum Erfassen eines breitbandigen Messsignals gemäß einer zweiten Ausführungsform der Erfindung; und

Fig. 4

einen weiteren Stromlaufplan einer Schaltungsanordnung zum Erfassen eines Messsignals.

For a better understanding of the present invention, reference will now be made to the preferred embodiments illustrated in the drawings, which are described by reference to specific terminology. It is to be understood, however, that the scope of the invention should not be so limited since such changes and other modifications to the illustrated devices, as well as such other uses of the invention as set forth herein, are deemed to be common current or future knowledge of a person skilled in the art , The figures show embodiments of the invention, namely:

Fig. 1

a circuit diagram of a known circuit arrangement for detecting an ion current between the electrodes of a spark plug of an internal combustion engine;

Fig. 2

the circuit diagram of a circuit arrangement for detecting a broadband measurement signal according to a first embodiment of the invention;

Fig. 3

a circuit diagram of a circuit arrangement for detecting a broadband measurement signal according to a second embodiment of the invention; and

Fig. 4

a further circuit diagram of a circuit arrangement for detecting a measurement signal.

In Fig. 1 a circuit diagram of a known circuit arrangement for generating a Zündlichtbogens, the so-called spark, using a spark plug 10 is shown. The high voltage required to generate the arc is generated by means of a transformer 20. The transformer 20 has a primary winding 12 and a secondary winding 14, which are magnetically coupled together via an iron core 13. One terminal of the primary winding 12 is permanently connected to the positive pole of the battery voltage Ubatt of a battery 16 of a motor vehicle. The negative pole of the battery 16 is connected to the ground of the motor vehicle, which serves as a reference potential. An electronic control unit 18 generates drive pulses for driving a power output stage formed by an IGBT power transistor and supplies these control pulses as a drive signal to a control terminal (gate) of the IGBT power transistor via a series resistor Rz.

Depending on the drive signal, the IGBT power transistor connects the second terminal of the primary winding 12 to the ground. A first terminal of the secondary winding 14 is connected to the high voltage electrode of the spark plug 10. Another electrode of the spark plug 10 is connected to the vehicle ground. The two electrodes are arranged at a distance from each other and form a spark gap over which an arc is generated with the aid of the high voltage generated by the ignition transformer 20. The second terminal of the secondary winding 14 is connected to a measuring circuit 22, which contains a power source 24 and a measuring resistor Rm. The energy source 24 comprises a capacitor C1 and a varistor ZPD arranged parallel to the capacitor C1. The power source 24, the measuring resistor Rm, the secondary winding 14 and the spark gap of the spark plug 10 are connected in series and form a closed circuit via the vehicle ground.

The control unit 18 generates a drive signal, by which the IGBT power transistor connects the second terminal of the primary winding 12 to ground, so that a closed circuit is formed, through which the battery voltage Ubatt is applied to the primary winding 12. As a result, a primary current flows through the primary winding 12. This primary current generates a magnetic field, by which a magnetic flux is generated. When the magnetic field builds up after the primary current flows, the magnetic flux caused by the magnetic field changes. The change in the magnetic flux induces a voltage in the secondary winding 14. This induced voltage is applied to the electrodes of the spark plug 10. If the induced voltage is small enough, ie, as long as the induced voltage has not reached the required breakdown voltage of the spark plug 10, no spark is generated. By the inserted diode D1, however, prevents the voltage induced in the secondary winding 14 at all applied to the electrodes of the spark plug 10, whereby a spark when switching on the primary winding 12 regardless of the height of the induced voltage is reliably prevented.

To generate the spark, the controller 18 drives the IGBT power transistor to disconnect the ground and primary winding 12. Due to the separation, the primary current flowing through the primary winding 12 is interrupted abruptly, whereby the magnetic field caused by the primary current collapses. The magnetic flux in the magnetic circuit of the ignition transformer 20 is thereby rapidly changed relatively strong. This change in the magnetic flux causes the induction of a high voltage in the secondary winding 14, whereby the voltage applied between the electrodes of the spark plug 10 exceeds the breakdown voltage of the spark plug 10 and causes a high voltage discharge.

By the secondary side induced high voltage and the capacitor C1 of the power source 24 is charged, the voltage drop across the varistor ZPD determines the charging voltage of the capacitor C1. Furthermore, the measuring resistor Rm and the varistor ZPD affect the current flow in the secondary circuit during the application of the high voltage, whereby the energy available for generating the arc in the secondary circuit is considerably reduced. After the arc is torn between the electrodes of the spark plug 10, the power source 24 feeds the secondary circuit, whereby a current flows through the secondary winding 14 via the electrodes of the spark plug 10, the ground connection of the motor vehicle and the measuring resistor Rm. By means of the voltage drop generated thereby via the measuring resistor Rm, an ion current present between the electrodes of the spark plug 10 can be detected. The secondary circuit serves as a measuring circuit. In this measuring circuit, the secondary winding 14 of the transformer 20 is arranged in series with the measuring resistor Rm and the spark gap of the spark plug 10. Due to the inductance of the secondary winding 14, short-term, ie relatively high-frequency, fluctuations of the charge carriers present between the electrodes of the spark plug 10, in particular of the ion current, do not become effective at the measuring resistor Rm. The secondary winding 14 thus serves as a low-pass filter, whereby only a relatively narrowband signal of the ion current between the electrodes of the spark plug 10 is available. The signal thus only reflects low-frequency changes in the ion current.

In Fig. 2 a circuit diagram of a circuit arrangement according to a first embodiment of the invention is shown. Like elements have the same reference numerals. The primary-side wiring of the transformer 20 agrees with the in Fig. 1 shown wiring. The secondary circuit, ie the high-voltage circuit, has three parallel current paths, the secondary winding 14 of the transformer 20 being arranged in the first current path, and the energy source 24 and the spark gap formed by the electrodes of the spark plug 10 being arranged in the second current path. In the third current path, a voltage divider formed from three resistors R1, R2 and Rm is arranged. The iron core 13 of the ignition transformer 20 is used as an electrical conductor for connecting the resistors R1 and R2. The iron core 13 thus forms a portion of the third current path. Further, in the first current path, a diode D1 is arranged in series with the secondary winding 14, which conducts current through the already associated with Fig. 1 described switch-on prevents.

Further, the diode D1 prevents current flow through the first path when, with the aid of the power source 24, a measuring voltage is applied in a measuring circuit formed by the spark plug 10 electrodes and the voltage divider formed by the resistors R1, R2 and Rm. The measuring circuit is thus decoupled by means of the diode D1 from the secondary winding 14, so that the secondary winding 14, in contrast to the in Fig. 1 shown circuit arrangement does not act as a low-pass filter.

The voltage divider formed by the resistor R1 and the total resistance of the resistors R2 and Rm sets the potential of the iron core 13 of the transformer 20 during the application of the high voltage in the secondary circuit. The sum of the resistors R1, R2 and Rm should be ≥ 1 megohm to reduce the current flow across this third current path, thus providing the spark plug 10 with sufficient energy to generate the arc. Preferably, the resistance of the sum of the resistors R1, R2 and Rm is in the range of 10 to 100 megohms, and the resistance of the resistor R1 may be 0 ohms, as hereinafter FIG. 3 explained. With the aid of the voltage divider formed from the resistors R1 and the total resistance of the resistors R2 and Rm, the potential of the iron core 13 can be easily adjusted. For example, the resistors R1 and the total resistance of the resistors R2 and Rm can be made the same size, so that the iron core 13 has approximately a high voltage potential, which corresponds to a floating core in the prior art.

In particular, in the case of rod transformers which are plugged directly onto the spark plug screwed into a cylinder head of a motor vehicle, the measurement signal can be simply passed from one end of the iron core 13 to the other end of the iron core 13 via the iron core 13 serving as an electrical conductor, thereby providing a simple structural design of the bar transformer is possible without requiring additional signal lines for conducting the measurement signal from one end of the bar transformer to the other end.

In Fig. 3 a circuit arrangement according to a second embodiment of the invention is shown, which is similar to the circuit arrangement according to Fig. 2 is. Unlike the in Fig. 2 shown circuit arrangement omitted in the circuit arrangement Fig. 3 the resistance R1, so that the iron core 13 has substantially the high voltage potential generated by the secondary winding 14. Specifically, the iron core 13 has a potential during an ignition process, which is compared to the high voltage potential of the secondary winding 14 by the voltage drop of the diode D1, that is reduced by 0.7 volts. During the measuring process, ie following the ignition process, the iron core 13 then has the potential of the measurement voltage generated by the energy source 24. As already mentioned, the turn-on pulse is blocked by the diode D1 in the secondary circuit, so that the voltage generated by the turn-on pulse in the secondary coil 14 is not applied to the iron core 13 of the transformer 20. Furthermore, diode D1 serves as decoupling means for decoupling the measuring circuit consisting of spark plug 10, voltage source 24, and resistors R2 and Rm or R1, R2 and Rm from secondary winding 14 during a current flow in the measuring circuit caused by voltage source 24. By the diode D1 is thus prevented that when feeding the measuring circuit with the measuring voltage, a current flows through the secondary winding 14.

The measuring signal is preferably conducted via a path parallel to the secondary winding 14. The resistance values of the tension divider formed from the resistors R1 and the total resistance from the resistors R2 and Rm should be chosen so large that the capacitive coupling of the iron core 13 is maintained. As an alternative to the resistors R1 or R2, a resistive bobbin or coating of the iron core 13 or a portion of the iron core 13 may also be provided with a resistive material, i. with a resistive coating, whereby further constructive advantages are achieved.

With the help of in the Figures 2 and 3 Circuit arrangements shown, it is possible to use ignition transformers 20 with spark energies of> 35 mJ and yet ion currents and other high-frequency signal components high voltage side to eat. A knock detection in the occurrence of explosive burns, which is too fast for the mechanical movement of the piston, can be determined automatically with the aid of the circuit arrangements according to the invention with conventional ignition transformers, in particular with Stabzündtransformatoren. Even with these conventional ignition transformers, despite the measuring circuit, sufficient spark energy is provided over the entire speed-load range of the internal combustion engine. For generating the measuring voltage by means of the energy source 24, only relatively little energy is withdrawn from the secondary circuit for charging the capacitor C1 of the energy source 24.

The secondary-side high voltage is measured in the third branch directly via the ohmic voltage divider R1, R2, Rm or R2, Rm. Thus, the inductance of the secondary coil 14 is not in the measuring branch and thereby does not act as a low-pass filter. The measurable frequency components of the spark plug voltage, which can be detected by means of the voltage drop across the measuring resistor Rm, are limited only by the capacitive coupling of the iron core 13 of the ignition transformer 20 and by the resistors of the voltage divider R1, R2, Rm and R2, Rm. As a result, the bandwidth of the measured signal is essentially limited only by the capacitive coupling of the iron core 13 of the ignition transformer 20 and by the resistors of the voltage divider R1, R2, Rm and R2, Rm,

The in the Fig. 2 and 3 Circuit arrangements shown serve as measuring circuits by which the curves of the voltage applied between the electrodes of the spark plug 10 candle voltage can be precisely detected. As a result, both the burning time, the burning voltage, the breakdown voltage and the rise in the spark plug voltage before the flashover, ie before the arc, between the electrodes of the spark plug 10 can be detected exactly.

In Fig. 4 is a circuit diagram of another embodiment of a control of an evaluation circuit shown. Unlike the arrangements after Fig. 2 and 3 is in the first current path, a varistor VAR1 arranged, the additional one Voltage drop in the first current path causes. This voltage drop then causes a reduction of the spark plug 10 available ignition energy. Furthermore, the measuring signal via the measuring resistor Rm or the high voltage potential applied to the varistor VDR1, in particular in the case of bar transformers, has to be guided relatively costly to a connection region of the bar transformer.

LIST OF REFERENCE NUMBERS

10

spark plug

12

primary

13

iron core

14

secondary winding

16

battery

18

control unit

20

transformer

22

measuring circuit

24

Energy source / voltage source

IGBT

power transistor

March

dropping resistor

U_batt

battery voltage

C1

capacitor

ZPD, ZPD1, ZPD3

varistor

R1, R2

resistance

rm

measuring resistor

D1,

diode

Claims (18)

1. Arrangement for detecting a broad-band measuring signal on a high-voltage side,
   comprising three parallel current paths,
   wherein in the first current path at least the secondary winding (14) of an ignition transformer (20) is arranged,
   wherein in the second current path at least the spark gap of the ignition plug (10) formed by at least two electrodes (10) is arranged, and
   wherein in the third current path at least one measuring resistor (Rm) is arranged,
   characterized in that at least in a region between a connection of the secondary winding (14) and the measuring resistor (Rm) at least a portion of the transformer core (13) of the ignition transformer (20) serves as electric conductor.
2. Arrangement according to claim 1, characterized in that the transformer core (13) is an iron core.
3. Arrangement according to claim 1 or 2, characterized in that between the connections of the secondary winding (14) and the ends of the third current path no variable resistor is arranged.
4. Arrangement according to one of the preceding claims, characterized in that the voltage drop via the measuring resistor (Rm) serves as a signal for detecting the ion current between the electrodes of the ignition plug (10), and that preferably an evaluation circuit for detecting the voltage drop via the resistor (Rm) is provided.
5. Arrangement according to one of the preceding claims, characterized in that an energy source (24) for producing the energy required for detection of the broad-band measuring signal is provided.
6. Arrangement according to claim 5, characterized in that the energy source (24) is arranged in the second or third current path, preferably in the second current path in a row with regard to the spark gap formed by the electrodes of the ignition plug (10).
7. Arrangement according to claim 5 or 6, characterized in that the energy source (24) is provided with a condenser (C1) that is preferably also charged during the presence of high-voltage at the electrodes of the ignition plug (10).
8. Arrangement according to claim 7, characterized in that parallel to the condenser (C1) a component (ZPD) for limiting the charging voltage of the condenser (C1) is provided, wherein this component (ZPD) is preferably a varistor.
9. Arrangement according to claim 7 or 8, characterized in that the condenser (C1) is connected in series with the spark gap of the ignition plug (10).
10. Arrangement according to one of the preceding claims, characterized in that in the first current path a diode (D1) is connected in series with the secondary winding (14) in order to prevent a current flow through the secondary winding (14) during the detection of the broad-band measuring signal and/or the signal corresponding to the ion current between the electrodes of the ignition plug (10).
11. Arrangement according to one of the preceding claims, characterized in that in the third current path at least a second resistor (R1, R2) is connected in series with the measuring resistor (Rm) that together with the measuring resistor forms a voltage divider.
12. Arrangement according to claim 11, characterized in that the measuring resistor (Rm) and the second resistor are connected electrically conductive via the transformer core (13) of the ignition transformer (20).
13. Arrangement according to claim 11, characterized in that the second resistor (R1) and a high-voltage connection of the secondary winding (14) are connected electrically via the transformer core (13) of the ignition transformer (20).
14. Arrangement according to claim 11, characterized in that in the third current path at least a third resistor (R1) is connected in series with the second resistor (R2) and the measuring resistor (Rm), wherein the second resistor (R2) and the third resistor (R1) are connected electrically via the transformer core (13) of the ignition transformer (20).
15. Arrangement according to claim 14, characterized in that the third resistor (R1) is arranged between a first connection of the secondary winding (14) and the transformer core (13) of the ignition transformer (20) and that the measuring resistor (Rm) and the second resistor (R2) are arranged between the transformer core (13) of the ignition transformer (20) and the second connection of the secondary winding (14), wherein preferably the second connection of the secondary winding (14) is connected with a reference potential.
16. Arrangement according to claim 15, characterized in that the third resistor and the total resistance of the second resistor (R2) and the measuring resistor (Rm) form a voltage divider via which the potential of the transformer core (13) of the ignition transformer (20) is determined.
17. Arrangement according to one of the preceding claims, characterized in that the second resistor (R2) and/or the third resistor (R1) and/or the measuring resistor (Rm) are formed by means of a resistive coating on the lateral surface of the iron core (13).
18. Arrangement according to one of the preceding claims, characterized in that the ends of the third current path are directly connected via a diode (D1) with each connection of the secondary winding (14) of the ignition transformer (20).

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