Ignition system and method for checking electrodes of a spark plug of an internal combustion engine

Abstract

A method for checking electrodes of a spark gap of an ignition system for a combustion chamber of an internal combustion engine with an externally provided ignition includes generating a spark at the spark gap in an operating state without ignition of an ignitable mixture in the combustion chamber; ascertaining a parameter or characteristic function representing the spark current, the spark voltage, and/or the spark duration; comparing the parameter or the characteristic function to a reference; adapting an energy for a voltage buildup for a further spark generation for the mixture ignition and/or for maintaining an ignition spark for the mixture ignition, in particular for a future ignition process, as a function of a difference between the parameter or the characteristic function and the reference.

Claims

1. A method for operating an ignition system for generating a spark at a spark gap in a combustion chamber of an internal combustion engine with an externally supplied ignition, the method comprising: generating the spark at the spark gap in an operating state without ignition of an ignitable mixture in the combustion chamber; ascertaining, by an evaluation unit, a parameter or characteristic function representing at least one of the spark current, the spark voltage, and the spark duration; comparing, by the evaluation unit, the parameter or the characteristic function to a reference; adapting, by the evaluation unit, at least one of an amount and a duration of voltage at the spark gap for at least one of generating and maintaining a further ignition spark for ignition of the mixture as a function of a difference between the parameter or the characteristic function and the reference, determined as a result of the comparison; and generating and maintaining the further ignition spark at the spark gap for the ignition of the mixture, using the adapted voltage; wherein the generation of the further ignition spark is performed with a primary voltage generator, and wherein the further ignition spark is maintained using a step-up chopper.

2. The method of claim 1, wherein the reference is a first threshold value which is specified on the basis of the spark gap at an initial operation of the ignition system and while taking a maximally permitted wear into account.

3. The method of claim 1, wherein the voltage is adapted by increasing a voltage availability through the primary voltage generator or through the step-up chopper.

4. The method of claim 3, wherein: the reference is a first threshold value which is specified on the basis of the spark gap at an initial operation of the ignition system and while taking a maximally permitted wear into account; and the voltage availability at electrodes that are at the spark gap is increased in a step-by-step manner until a predefined second threshold value has been reached.

5. The method of claim 4, wherein, after the predefined second threshold value has been exceeded, a fault signal is output which indicates that an exchange of the electrodes is required.

6. The method of claim 1, wherein the comparing includes evaluating a profile of the characteristic function over the time.

7. The method of claim 1, wherein the spark that is generated at the spark gap in the operating state without the ignition is generated at an instant without a presence of an ignitable mixture.

8. The method of claim 1, wherein the spark that is generated at the spark gap in the operating state without the ignition is generated at an instant that is without a presence of an ignitable mixture and that features low turbulence in the combustion chamber.

9. The method of claim 1, wherein the spark that is generated at the spark gap in the operating state without the ignition is generated in an exhaust working stroke of the internal combustion engine.

10. The method of claim 1, wherein the spark that is generated at the spark gap in the operating state without the ignition is generated in an exhaust working stroke with closed intake valves of the internal combustion engine.

11. The method of claim 1, wherein the further ignition spark is maintained using a constant electrical power of a step-up chopper.

12. The method of claim 1, wherein the parameter is ascertained in an essentially stationary state.

13. The method of claim 1, wherein an electrical voltage is used as reference, the method further comprising: ascertaining whether an overshooting condition is satisfied by determining whether the spark voltage exceeds the reference; and at least one of increasing a voltage availability for spark generation and increasing an output power of a primary voltage generator or a step-up chopper if the overshooting condition is satisfied.

14. The method of claim 13, wherein the increasing of the output power of the step-up chopper is performed, the increasing being by increasing at least one of a spark current and an output current of the step-up chopper.

15. The method of claim 1, wherein an electrical current is used as reference, the method further comprising: ascertaining whether an undershooting condition is satisfied by determining whether the spark current or an output current of a step-up chopper undershoots the reference; and at least one of increasing a voltage availability for spark generation and increasing an output power of a primary voltage generator or a step-up chopper if the undershooting condition is satisfied.

16. The method of claim 15, wherein the increasing of the output power of the step-up chopper is performed, the increasing being by increasing at least one of a spark current and an output current of the step-up chopper.

17. The method as recited in claim 1, wherein the evaluation unit includes one of: (i) a programmable processor, (ii) a programmable controller, (iii) an ASIC, or (iv) a Field Programmable Gate Array.

18. The method as recited in claim 1, the adapting includes increasing the at least one of the amount and the duration of the voltage at the spark gap using a step-up chopper.

19. An ignition system for an internal combustion engine with externally provided ignition, the ignition system comprising: a spark gap; a primary voltage generator; and an evaluation unit, wherein the evaluation unit is configured to: use the primary voltage generator to generate a spark at the spark gap in an operating state without ignition of an ignitable mixture in the combustion chamber; ascertain a parameter or characteristic function representing at least one of the spark current, the spark voltage, and the spark duration; compare the parameter or the characteristic function to a reference; adapt at least one of an amount and a duration of voltage at the spark gap for at least one of generating and maintaining a further ignition spark for ignition of the mixture as a function of a difference between the parameter or the characteristic function and the reference, determined as a result of the comparison; and generate and maintain the further ignition spark at the spark gap for the ignition of the mixture, using the adapted voltage; wherein the generation of the further ignition spark is performed with a primary voltage generator, and wherein the further ignition spark is maintained using a step-up chopper.

20. The ignition system of claim 19, furthermore comprising: a step-up chopper whose output lies in an electrical loop with the spark gap and that is configured to inject a predefined electrical quantity in order to maintain the further ignition spark.

21. The ignition system of claim 20, wherein the predefined electrical quantity is at least one of an output current, an output voltage, and an output power into the spark gap.

22. The ignition system of claim 19, wherein the evaluation unit is configured to adapt an operating mode of the step-up chopper or a primary voltage generator in response to the result of the comparison.

23. The ignition system as recited in claim 19, wherein the evaluation unit includes one of: (i) a programmable processor, (ii) a programmable controller, (iii) an ASIC, or (iv) a Field Programmable Gate Array.

24. The ignition system as recited in claim 19, wherein the primary voltage generator provides at least one of an increased voltage, an increased current, and an increased power, to electrodes at the spark gap to generate the further ignition spark at the spark gap.

25. A method for operating an ignition system for generating a spark at a spark gap in a combustion chamber of an internal combustion engine having externally supplied ignition, the method comprising: generating the spark at the spark gap using a primary voltage generator; ascertaining a parameter; comparing the parameter to a reference; adapting an energy, as a function of a difference between the parameter and the reference, for at least one of: (i) a voltage buildup for the spark generation, and (ii) maintaining an ignition spark for ignition of an ignitable mixture in the combustion chamber, as a function of a difference between the parameter and the reference, wherein the adapting is for a future ignition process; wherein, in the generating step, the spark at the spark gap is generated in an operating state without ignition of the ignitable mixture in the combustion chamber and is maintained by a step-up chopper so that the parameter correlates with an electrode state or electrode gap at the spark gap; wherein, in the ascertaining step, at least one of a spark current and the spark voltage is ascertained as the parameter; and wherein a value of the reference is a first threshold value which is specified based on the electrode gap at an initial operation of the ignition system and while taking a maximally permitted wear into account; and wherein the method further comprises using the adapted energy in the future ignition process to at least one of generate and maintain a further ignition spark at the spark gap for the ignition of the mixture.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 a circuit diagram of an ignition system according to an example embodiment of the present invention.

(2) FIG. 2 illustrates crank-angle ranges in which the ignition spark is advantageously able to be generated according to an example embodiment of the present invention.

(3) FIG. 3 a flow diagram that illustrates steps of an exemplary embodiment of a method according to an example embodiment of the present invention.

DETAILED DESCRIPTION

(4) FIG. 1 shows a circuit of an ignition system 1, which includes a step-up transformer 2 as a high-voltage generator, whose primary side 3 is able to be supplied with electrical energy from an electrical energy source 5 via a first switch 30. Secondary side 4 of step-up transformer 2 is supplied with electrical energy via an inductive coupling of primary coil 8 and secondary coil 9 and has a diode 23, known from the related art, for a switch-on spark suppression; this diode 23 may alternatively be replaced with diode 21. A spark gap 6 relative to ground 14, via which ignition current i.sub.2 is to ignite the combustible gas mixture, is provided in a loop with secondary coil 9 and diode 23. After an ignition has taken place, a usually fluctuating spark voltage U.sub.brenn is applied at spark gap 6. According to the present invention, a step-up chopper 7 is provided between electrical energy source 5 and secondary side 4 of step-up transformer 2. Furthermore, an inductivity 15 is connected with a capacity 10 via a switch 22 and a diode 16. One end of capacity 10 is connected to secondary coil 9 and its other end is connected to electrical ground 14. The inductivity serves as an energy store in this case for maintaining a current flow. Diode 16 is conductively oriented in the direction of capacity 10. A shunt 19 as a current-measuring means or a voltage-measuring means is provided between capacity 10 and secondary coil 9, its measuring signal being supplied to switch 22 as well as to switch 27. In this way switches 22, 27 are designed to react to a defined range of current intensity i.sub.2 through secondary coil 9. The terminal of switch 22 facing diode 16 is able to be connected to electrical ground 14 via a further switch 27. To protect capacity 10, a Zener diode 21 is switched in parallel with capacity 10 in the reverse direction. In addition, switch signals 28, 29 are sketched through which switches 22, 27 are able to be controlled. While switch signal 28 represents a switch-on and remain closed for an entire ignition cycle, switch signal 29 sketches a simultaneous alternating signal between closed and open. With a closed switch 22, inductivity 15 is supplied with a current via electrical energy source 5, the current flowing directly to electrical ground 14 when switches 22, 27 are closed. Given an open switch 27, the current is forwarded to capacitor 10 via diode 16. The voltage that comes about in response to the current into capacitor 10 is added to the voltage dropping over secondary coil 9 of step-up transformer 2, whereby the arc at spark gap 6 is supported. However, capacitor 10 is discharged in the process so that by closing switch 27, energy is able to be brought into the magnetic field of inductivity 15 in order to charge this energy back to capacitor 10 in a renewed opening of switch 27. As can be seen, actuation 31 of switch 30 provided in primary side 3 is kept clearly shorter than is the case for switches 22 and 27. Since switch 22 does not assume any essential function for the processes according to the present invention but simply switches the circuit on or off, it is optional and can therefore also be omitted. If an instant at which spark voltage U.sub.brenn is essentially independent of the gas mixture inside the combustion chamber is selected for the generation of the spark at spark gap 6 according to the present invention, electrical parameters at spark gap 6 are able to be evaluated in evaluation unit 36 of the ignition system, e.g., via shunt 19, in order to draw conclusions with regard to the electrode gap. Through output-side capacity 10, step-up chopper 7 provides an electrical power at P0 adapted in response to the aforementioned evaluation in order to bring the duration of the ignition spark as well as spark current i.sub.2 into value ranges that are suitable for a reliable mixture ignition.

(5) FIG. 2 shows suitable ranges, relative to the crank angle, for generating the spark proposed according to an example embodiment. While the sparks illustrated for the mixture ignition at a crank angle of 0 and a crank angle of 720 are used for igniting the mixture, marked crank angle ranges 13 between 180 and 360 as well as between 900 and 1080 are suitable for generating a spark at the spark gap without igniting an ignitable mixture in the combustion chamber. In particular, relatively low pressures and turbulences prevail in these crank angle ranges so that relatively little energy is required to generate the spark.

(6) FIG. 3 shows steps of an exemplary embodiment of a method according to the present invention. In step 100, a spark at the spark gap is generated in an operating state without ignition of an ignitable mixture in the combustion chamber. Preferably, the spark is therefore generated in an exhaust working stroke. In step 200, a characteristic function that represents the spark current is ascertained over the time and compared with a predefined reference in step 300. In the process, the necessity for increasing the spark current in step 400 is determined due to a greater electrode gap as a result of erosion; this is accomplished by increasing the output power of a step-up chopper used for maintaining the ignition spark. In order to document the advanced state of erosion of the electrodes despite a maintained operational readiness of the ignition system according to the present invention, in step 500 an entry in a fault memory is made, which suggests an exchange of the spark plugs during the next service appointment.

(7) According to the present invention, the forwarding of the wear information to the onboard diagnosis (OBD), for example, may be used for a need-based exchange of the spark plugs and otherwise for an adaptation of the electrical parameters of the ignition system to the current wear state. In addition, the present invention makes it possible to reduce the provision of additional electrical energy that is always required according to the related art for ensuring a proper ignition process. The analysis according to the present invention makes it possible to reduce these safety reserves and thus to increase the efficiency of the ignition system. Furthermore, a need-based supply of electrical energy reduces the spark erosion at the electrodes. The thermal and electrical loading of the components of the ignition system are able to be reduced as well.

(8) In real applications, for example, the method according to the present invention is able to be carried out every 1000 km of driving distance for vehicles equipped with the ignition system according to the present invention. For internal combustion engines used in a stationary manner, an execution every 5 to 10 hours of service, for example, may be provided. Of decisive importance is to ensure that the conditions in the combustion chamber are constant in each case. In other words, the temperature, pressure, and the flow rate must be known or predictable, at least within narrow limits. A suitable operating state is an idling state with a predefined oil/cooling water temperature, for instance.

(9) Notwithstanding the fact that the aspects of the present invention and the advantageous specific embodiments have been described in detail on the basis of the exemplary embodiments in conjunction with the figures of the drawing, one skilled in the art will derive modifications and combinations of features in the exemplary embodiments illustrated without departing from the scope of the present invention, whose protective scope is defined by the attached claims.