Method for controlling a corona ignition device

Abstract

Disclosed is an inventive method for controlling a corona ignition device of an internal combustion engine. A corona discharge, which ignites fuel in a combustion chamber of the engine, is generated by applying a voltage to the corona ignition device. An actual value that is characteristic of the nitrogen oxide concentration of the exhaust gas is compared with a setpoint value, and, if the actual value deviates from the setpoint value by more than a specified threshold value and the actual value is greater than the setpoint value, the voltage is reduced after the comparison.

Claims

1. A method for controlling a corona ignition device of an internal combustion engine, the method comprising: applying a voltage to the corona ignition device and thereby generating a corona discharge, the corona discharge igniting fuel in a combustion chamber of the engine; determining nitrogen oxide concentration in exhaust gas of the internal combustion engine; comparing the determined nitrogen oxide concentration with a setpoint value for nitrogen oxide concentration in the exhaust gas; and reducing the voltage applied to the corona ignition device after the comparison when the determined nitrogen oxide concentration is greater than the setpoint value by more than a first predetermined threshold amount and thereby reducing the amount of nitrogen oxide in the exhaust gas.

2. The method according to claim 1, wherein the step of determining nitrogen oxide concentration comprises measuring nitrogen oxide concentration using a sensor.

3. The method according to claim 1, wherein the step of determining nitrogen oxide concentration comprises calculating nitrogen oxide concentration from engine operating data.

4. The method according to claim 3, wherein the engine operating data includes combustion temperature or ignition delay.

5. The method according to claim 1, wherein the voltage is changed in steps as a result of the comparison of the determined nitrogen oxide concentration and the setpoint value, the size of the steps being independent of the extent of deviation of the determined nitrogen oxide concentration from the setpoint value.

6. The method according to claim 1, wherein the voltage applied to the corona ignition device is a high-frequency alternating voltage generated from a primary voltage using a voltage converter.

7. A method for controlling a corona ignition device of an internal combustion engine, the method comprising: applying a voltage to the corona ignition device and thereby generating a corona discharge, the corona discharge igniting fuel in a combustion chamber of the engine; determining nitrogen oxide concentration in exhaust gas of the internal combustion engine; comparing the determined nitrogen oxide concentration with a setpoint value for nitrogen oxide concentration in the exhaust gas; and increasing the voltage applied to the corona ignition device after the comparison when the determined nitrogen oxide concentration is less than the setpoint value by more than a first predetermined threshold amount and thereby increasing the amount of nitrogen oxide in the exhaust gas.

8. The method according to claim 7, wherein the step of determining nitrogen oxide concentration comprises measuring nitrogen oxide concentration using a sensor.

9. The method according to claim 7, wherein the step of determining nitrogen oxide concentration comprises calculating nitrogen oxide concentration from engine operating data.

10. The method according to claim 9, wherein the engine operating data includes combustion temperature or ignition delay.

11. The method according to claim 7, further comprising specifying a maximum value of the voltage not to be exceeded, independently of the determined nitrogen oxide concentration.

12. The method according to claim 11, wherein the maximum value of the voltage not to be exceeded is determined dynamically by evaluating electrical characteristic variables of an oscillator circuit in the corona ignition device.

13. The method according to claim 7, wherein the voltage is changed in steps as a result of the comparison of the determined nitrogen oxide concentration and the setpoint value, the size of the steps being independent of the extent of deviation of the determined nitrogen oxide concentration from the setpoint value.

14. The method according to claim 7, wherein the voltage applied to the corona ignition device is a high-frequency alternating voltage generated from a primary voltage using a voltage converter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 schematically shows the structure of an ignition system for an internal combustion engine.

DETAILED DESCRIPTION

(3) The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure.

(4) FIG. 1 shows a combustion chamber 1, which is delimited by walls 2, 3 and 4, which are at ground potential. An ignition electrode 5 projects into the combustion chamber 1 from above, said ignition electrode being surrounded over some of its length by an insulator 6, with which it is guided in an electrically insulated manner through the upper wall 2 into the combustion chamber 1. The ignition electrode 5 and the walls 2 to 4 of the combustion chamber 1 are part of an oscillator circuit 7, which also includes a capacitor 8 and an inductance 9. Of course, the oscillator circuit 7 can have further inductances and/or capacitors and other components that are known to a person skilled in the art as possible components of oscillator circuits.

(5) To excite the oscillator circuit 7, a DC/AC converter is provided, which in the example shown is formed by a high-frequency generator 10, which has a DC voltage source 11 and a transformer 12, which has a central pickup 13 on its primary side, as a result of which two primary windings 14 and 15 meet at the central pickup 13. To generate a corona discharge, a primary voltage is applied to the DC/AC converter, specifically to the central pickup 13. The primary voltage can be generated from the voltage of the DC voltage source 11, for example by a pulse-width modulation process, and thus adjusted to a desired value.

(6) The effective value of this primary voltage can be regarded as the voltage that is applied to the corona ignition device and reduced when an actual value that is characteristic of the nitrogen oxide concentration of the exhaust gas deviates by more than a specified threshold value from a setpoint value and the actual value is greater than the setpoint value. It is also possible for the primary voltage to be generated with a further voltage converter, which is supplied with a DC voltage or an alternating voltage, which can originate for example from the general electricity grid in the case of a stationary engine. If the voltage converter is not regarded as part of the corona ignition device, the high-frequency alternating voltage with which the oscillator circuit is excited can be regarded as the voltage that is applied to the corona ignition device and reduced when an actual value that is characteristic of the nitrogen oxide concentration of the exhaust gas deviates by more than a specified threshold value from a setpoint value and the actual value is greater than the setpoint value.

(7) The ends of the primary windings 14 and 15 remote from the central pickup 13 are connected alternately to earth by means of a high-frequency selector switch 16. The switching frequency of the high-frequency selector switch 16 defines the frequency at which the series oscillator circuit 7 is excited and is variable. The secondary winding 17 of the transformer 12 supplies the series oscillator circuit 7 at point A. The high-frequency selector switch 16 is controlled with the aid of a regulating circuit such that the oscillator circuit is excited at its resonant frequency. The voltage between the tip of the ignition electrode 5 and the walls 2 to 4 at earth potential is then at its greatest.

(8) While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

REFERENCE NUMBERS

(9) 1 Combustion chamber 2 Wall of combustion chamber 3 Wall of combustion chamber 4 Wall of combustion chamber, top of piston 18 5 Ignition electrode 6 Insulator 7 Oscillator circuit, series oscillator circuit 8 Capacitor 9 Inductance 10 High-frequency generator 11 DC voltage source 12 Transformer 13 Central pickup 14 Primary winding 15 Primary winding 16 High-frequency selector switch 17 Secondary winding