Method for operating an ignition system and a corresponding ignition system

Abstract

An ignition system and a method for suppressing an ignition spark discharge at a spark gap at an unsuitable time are provided. The method includes a recognition of a spark breakaway and/or a failed ignition and, in response thereto, by producing a conductive path via an ignition spark at the spark gap at a suitable time.

Claims

1. A method for operating an ignition system for an internal combustion engine, the ignition system including a voltage generator and a spark gap for producing an ignition spark, the method comprising: recognizing at least one of a spark breakaway and a failed ignition by performing the following: ascertaining a secondary-side current or a secondary-side voltage, ascertaining whether an exceeding condition is met by ascertaining whether a change in the secondary-side current or the secondary-side voltage exceeds a specified first threshold value, ascertaining whether an ignition condition is met by ascertaining whether no ignitable mixture is present in a combustion chamber of an internal combustion engine, the ignition condition being met if no ignitable mixture is present in the combustion engine of the internal combustion engine; and producing, in response thereto, a conductive path via an ignition spark at the spark gap in a working stroke (I, II, III, IV) of the internal combustion engine if the exceeding condition and the ignition condition are met, in which a combustion (III) and/or an ejection (IV) of fluid from a combustion chamber containing the spark gap takes place, and/or in which an intake (I) and/or compression (II) takes place, and in which residual energy stored in at least one electrical energy storage device of the ignition system is below a specified threshold value.

2. The method of claim 1, wherein the ignition system includes a step-up converter for maintaining an ignition spark that includes an electrical capacitance for the intermediate storage of ignition energy, and wherein the recognizing and producing tasks include the following: ascertaining whether a state condition is met by ascertaining whether the step-up converter of the ignition system is switched off, measuring an output voltage of the step-up converter, ascertaining whether an exceeding condition is met by ascertaining whether the measured output voltage exceeds a specified second threshold value, ascertaining whether an ignition condition is met by ascertaining whether no ignitable mixture is present in a combustion chamber of an internal combustion engine, and producing a conductive path via an ignition spark if the state condition, the exceeding condition, and the ignition condition are met.

3. The method of claim 1, wherein the ignition system includes a step-up converter for maintaining an ignition spark that includes an electrical capacitance for the intermediate storage of ignition energy, and wherein the recognizing and producing tasks include the following: ascertaining whether a state condition is met by ascertaining whether the step-up converter of the ignition system is switched on, measuring an ignition spark current, ascertaining whether a falling-below condition is met by ascertaining whether the measured ignition spark current falls below a specified third threshold value, ascertaining whether an exceeding condition is met by ascertaining whether a time difference between the time of the first falling below the third threshold value and an end of the operation of the step-up converter exceeds a specified fourth threshold value, ascertaining whether an ignition condition is met by ascertaining whether no ignitable mixture is present in a combustion chamber of an internal combustion engine, and producing a conductive path via an ignition spark when the falling-below condition, the state condition, the exceeding condition, and the ignition condition are met.

4. The method of claim 1, wherein the production of the conductive path occurs via the ignition spark at the spark gap following each ignition time of an operating state under consideration, or of all operating states, in particular with initiation of a signaling of a control device of the ignition system.

5. A machine-readable storage medium having a computer program, which is executable by a processor, comprising: a program code arrangement having program code for operating an ignition system for an internal combustion engine, the ignition system including a voltage generator and a spark gap for producing an ignition spark, by performing the following: recognizing, via the processor, at least one of a spark breakaway and a failed ignition by performing the following: ascertaining a secondary-side current or a secondary-side voltage, ascertaining whether an exceeding condition is met by ascertaining whether a change in the secondary-side current or the secondary-side voltage exceeds a specified first threshold value, ascertaining whether an ignition condition is met by ascertaining whether no ignitable mixture is present in a combustion chamber of an internal combustion engine, the ignition condition being met if no ignitable mixture is present in the combustion engine of the internal combustion engine; and producing, via the processor, in response thereto, a conductive path via an ignition spark at the spark gap in a working stroke (I, II, III, IV) of the internal combustion engine if the exceeding condition and the ignition condition are met, in which a combustion (III) and/or an ejection (IV) of fluid from a combustion chamber containing the spark gap takes place, and/or in which an intake (I) and/or compression (II) takes place, and in which residual energy stored in at least one electrical energy storage device of the ignition system is below a specified threshold value.

6. An ignition system for an internal combustion engine, comprising: an ignition device, including: a first electrode and a second electrode of a spark gap; a first voltage generator for producing an ignition spark; a control unit for controlling the voltage generator so as to operating the ignition device, the ignition system including the first voltage generator and the spark gap for producing the ignition spark, by performing the following: recognizing, via the processor, at least one of a spark breakaway and a failed ignition by performing the following: ascertaining a secondary-side current or a secondary-side voltage, ascertaining whether an exceeding condition is met by ascertaining whether a change in the secondary-side current or the secondary-side voltage exceeds a specified first threshold value, ascertaining whether an ignition condition is met by ascertaining whether no ignitable mixture is present in a combustion chamber of an internal combustion engine, the ignition condition being met if no ignitable mixture is present in the combustion engine of the internal combustion engine; and producing, via the processor, in response thereto, a conductive path via an ignition spark at the spark gap in a working stroke (I, II, III, IV) of the internal combustion engine if the exceeding condition and the ignition condition are met, in which a combustion (III) and/or an ejection (IV) of fluid from a combustion chamber containing the spark gap takes place, and/or in which an intake (I) and/or compression (II) takes place, and in which residual energy stored in at least one electrical energy storage device of the ignition system is below a specified threshold value.

7. The ignition system of claim 6, further comprising: a voltage sensor to detect, after an ignition time, an electrical voltage remaining in the ignition system, and to initiate, in response to an exceeding of a defined threshold value of the voltage and of a dead time, the production of the conductive path via the ignition spark at the spark gap.

8. The ignition system of claim 6, further comprising: a capacitance device that, in the case of an unsuccessful ignition, stores a voltage that is at least partly discharged via an ignition spark at the spark gap at a particular time.

9. The ignition system of claim 6, wherein the production of the conductive path via the ignition spark at the spark gap occurs via the same voltage generator that prepared the ignition spark discharge to be suppressed.

10. The method of claim 1, wherein the production of the conductive path via the ignition spark at the spark gap occurs via the same voltage generator that prepared the ignition spark discharge to be suppressed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic diagram of a part of an exemplary embodiment of an ignition system according to the present invention.

(2) FIG. 2 shows a schematic diagram of a part of an alternative exemplary embodiment of an ignition system according to the present invention.

(3) FIG. 3 shows a pressure-crankshaft angle diagram illustrating pressure relationships during various working strokes of an internal combustion engine.

(4) FIG. 4 shows a flow diagram illustrating steps of an exemplary embodiment of a method according to the present invention.

DETAILED DESCRIPTION

(5) FIG. 1 shows an ignition system 1 that has a transformer 2 having a primary side 3 and a secondary side 4 as voltage generator. Primary side 3 and secondary side 4 are magnetically coupled. Parallel to secondary side 4 are situated both a capacitance C and a spark gap F. Secondary side 4 is grounded to electrical ground 5 by an electrical contact.

(6) FIG. 2 shows an alternative exemplary embodiment of an ignition system 1 according to the present invention. In contrast to the configuration shown in FIG. 1, capacitance C is configured in series to secondary side 4 of transformer 2. Secondary side 4, capacitance C, and spark gap F are thus situated in a single common loop.

(7) FIG. 3 shows a schematic pressure curve in the combustion chamber of an internal combustion engine over the crank angle (measured in degrees crank angle). The four working strokes of an Otto engine are shown: intake I, compression II, combustion III, ejection IV. The strokes intake I and compression II represent a critical region X for the discharging of an uncontrolled spark. During a controlled ignition in the region of a transition from the second stroke compression II to the third stroke combustion III, a discharge of the ignition system according to the present invention should take place in the regions combustion III and ejection IV (as the recited suitable time). In this way, a discharge takes place before, via the remaining charge, in a following work cycle the critical region designated X enables a damaging, uncontrolled combustion. In regions I and II, a quenched spark can also be provoked; here care is to be taken that the discharge does not release enough energy to cause mixture combustion.

(8) FIG. 4 shows a flow diagram illustrating steps of an exemplary embodiment of a method according to the present invention.

(9) In step 100, an attempt is undertaken to ignite a mixture in the combustion chamber. The ignition attempt can fail, corresponding to a failed ignition, a critical spark current breakaway, or an excessive amount of remaining capacitively stored residual energy. This is recognized in step 200 by ascertaining and evaluating a secondary-side voltage and/or a secondary-side current. In the case of the evaluation of the secondary-side current, it is checked whether this current exceeds a specified threshold value. If this threshold value is exceeded, it is checked whether a suitable time is present for dismantling the residual energy, by ascertaining whether no ignitable mixture is present in a combustion chamber of an internal combustion engine. If no ignitable mixture is present in the combustion chamber, then in step 300 there takes place a second ignition, i.e. at a suitable time, which may take place in strokes III, IV (see FIG. 3).

(10) A core idea of the present invention is that after the combustion process, in an uncritical state, a discharge spark is produced at the spark plug electrodes in the combustion chamber, as can take place for example via a corresponding supply of current to, and switching off of, the primary coil of the ignition coil. Through the resulting discharge spark, there arises a conductive path via which the remaining energy of the capacitances of the secondary side of the ignition system can discharge. This process may be carried out with low turbulence in the combustion chamber. Due to the low turbulence, the spark breaks away at an uncritically low voltage value or current value. Thus, the stored energy is converted almost completely into spark. The residual energy corresponding to the low value of the spark current is below the energy required for an uncontrolled ignition. The method according to the present invention can be triggered optionally at each ignition, after a detected spark breakaway, or when there is a detected failed ignition (e.g. by omitting a main ignition in the region of top dead center, or of a spark breakaway).

(11) According to a first alternative, the production of an ignition spark in step 300 can take place internally in the ignition system, for example in an internal control device or in internal electronics modules. According to a second alternative, the production of an ignition spark can also be triggered by an external control device, for example an engine control device.

(12) In the exemplary embodiments according to FIG. 1 and FIG. 2, steps 200, 300 can include the following steps: the secondary-side current is ascertained and a spark breakaway and/or a failed ignition is recognized via an abrupt change in the secondary-side current. This takes place by checking whether the magnitude of the change of the secondary-side current exceeds a specified first threshold value. If this is the case, an exceeding condition is met.

(13) Instead of the secondary-side current, a secondary-side voltage can also be acquired that may be ascertained only after a specified temporal delay after a starting time of the method, in order to have a stationary state in the ignition system. The temporal delay is for example a function of rotational speed and/or is a function of a crankshaft angle. A spark breakaway and/or a failed ignition is recognized when the acquired secondary-side voltage exceeds a specified second threshold value. If this is the case, the exceeding condition is met.

(14) It is thereupon ascertained whether an ignition condition is met by checking whether no ignitable mixture is present in a combustion chamber of an internal combustion engine. If the exceeding condition and the ignition condition are met, in step 300 a conductive path is produced by an ignition spark.

(15) In a further exemplary embodiment, the ignition system additionally includes a step-up converter for maintaining an ignition spark. Such an ignition system having a step-up converter is disclosed for example in DE 10 2013 218227 A1, whose content is expressly incorporated in the disclosure of the present application.

(16) The step-up converter according to the present invention includes, as in DE 10 2013 218227 A1, an inductance, a switch, a capacitance C, and a diode. The inductance of the step-up converter is fashioned in the form of a transformer having a primary side and a secondary side. Here the inductance acts as an energy storage device for charging the capacitor. Capacitance C of the step-up converter is configured, as in FIG. 2, in series with secondary side 4 of transformer 2. The output power of the step-up converter is, with regard to FIG. 2, fed into secondary side 4 of ignition system 1 via a node point situated between secondary side 4 of transformer 2 and capacitance C, and is supplied to spark gap F. The output voltage of the step-up converter is correspondingly present at the stated node point.

(17) According to the present invention, in the further exemplary embodiment as well it is recognized that residual energy is present in an electrical capacitance C of the ignition system. Upon this recognition, at a suitable time an ignition spark is produced. Electrical capacitance C can be a capacitor of the step-up converter or a parasitic capacitance in the ignition system.

(18) In the exemplary embodiment having the step-up converter, step 200 includes the following steps: first, it is ascertained whether the step-up converter of the ignition system is switched off. If this is the case, an output voltage of the step-up converter is measured, in particular after expiration of a specified time period after the switching off of the step-up converter, in order to have a stationary state in the ignition system. Subsequently it is ascertained whether the measured output voltage exceeds a specified second threshold value. If the second threshold value is exceeded, an unsuccessful ignition can be inferred, because too much residual energy is stored in the capacitance of the step-up converter, so that there is the risk of an unintended ignition at an unsuitable time. Thereupon it is checked whether a suitable time for dismantling the residual energy is present, by ascertaining whether no ignitable mixture is present in a combustion chamber of an internal combustion engine. If no ignitable mixture is present in the combustion chamber, a suitable time is present and an ignition is initiated according to step 300.

(19) Alternatively, in the further exemplary embodiment the unsuccessful ignition can be determined by measuring an ignition spark current. In this case, step 200 includes the following steps: first, the ignition spark current is measured. Thereupon it is ascertained whether the measured ignition spark current falls below a specified third threshold value. If the current is below the third threshold value, an unsuccessful ignition can be inferred. Through the further operation of the step-up converter after the unsuccessful ignition, the voltage over the output capacitance of the step-up converter increases further, increasing the risk of an undesired spark discharge. Therefore, it is ascertained whether the unsuccessful ignition has taken place with switched-on or switched-off step-up converter. If the step-up converter is switched on, it is additionally ascertained whether a time difference between the time of the first falling below the second threshold value and a known end of the operation of the step-up converter exceeds a specified fourth threshold value. If the fourth threshold value has been exceeded, too much residual energy is stored in the capacitance of the step-up converter, so that there is the risk of an unintended ignition. Thereupon it is checked whether a suitable time is present for dismantling the residual energy, by ascertaining whether no ignitable mixture is present in a combustion chamber of the internal combustion engine. If no ignitable mixture is present in the combustion changer and the above conditions are met, the ignition is initiated according to step 300.

(20) A computer program can be provided that is set up to carry out all described steps of the method according to the present invention. The computer program is stored on a storage medium. Alternatively to the computer program, the method according to the present invention can be controlled by an electronic circuit provided in the ignition system, an analog circuit, or an ASIC or a microcontroller that is set up to carry out all described steps of the method according to the present invention.

(21) Although the aspects and advantageous specific embodiments according to the present invention have been described in detail on the basis of exemplary embodiments explained in connection with the accompanying drawings, a person skilled in the art will be capable of realizing modifications and combinations of features of the presented exemplary embodiments without departing from the scope of the present invention, whose scope of protection is defined by the entirety of the present application.