Method for determining a spark burning time during the operation of an ignition device

Abstract

Method for determining a spark burning time (Δt) during the operation of an ignition device (110) for an internal combustion engine (100) with a spark plug (130) and an ignition coil (120) with primary winding (121) and secondary winding (122), wherein for an ignition process, first, in an initial charging process (EL), the primary winding (121) is charged and a current flow in the primary winding (121) is interrupted, and subsequently, once or several times, in recharging processes (NL), the primary winding (122) is recharged and the current flow is interrupted, wherein during a charging of the primary winding (122) at least during one of the recharging processes (NL) a current flow (I) through the primary winding (121) is detected, and where, if an initial value of the current flow (I) through the primary winding (121) for the recharging process (NL) is below a predetermined threshold value (I S) is based on the time period between the interruption of the current flow in the primary winding (121) after the initial charging process (EL) and this recharging process (NL) the spark duration (Δt) is determined.

Description

[0001] The present invention relates to a method for determining a spark burning duration during the operation of an ignition device for an internal combustion engine, as well as a computing unit and a computer program for carrying it out. State of the art

[0002] In gasoline engines, such as those used in motor vehicles, or other internal combustion engines like gas turbines, ignition devices with a spark plug and an ignition coil are used to ignite a combustible fuel-air mixture at a desired time by generating a spark. The spark duration of such a spark, i.e., the length of time the spark burns at the spark plug after ignition begins, is an important parameter for controlling and evaluating ignition processes.

[0003] DE 10 2013 004 728 A1 discloses a method for operating an internal combustion engine in which the burning time of the first of several ignition sparks is determined and this spark is classified as a "gliding spark" or "air spark" based on its burning time in order to initiate measures to stabilize the combustion in the event of an accumulation of undesired gliding sparks.

[0004] DE 40 20 986 A1 discloses an electronic ignition system in which the duration of the ignition spark is determined from the voltage curve on the primary side of the ignition coil in order to enable a diagnosis of the ignition system.

[0005] DE 41 16 642 A1 discloses an ignition system for functional monitoring which measures both the ignition spark duration and the ignition voltage on the primary side and compares them with operating point-dependent limit values ​​in order to switch between different monitoring methods.

[0006] US 2018 / 0135590 A1 describes an ignition control system that directly measures the ignition spark duration by monitoring a voltage reflection on the primary side of the ignition coil and dynamically adjusts the coil dwell time to achieve and maintain a predetermined target spark duration. Disclosure of the invention

[0007] According to the invention, a method for determining a spark burning duration, as well as a computing unit and a computer program for carrying it out, are proposed, comprising the features of the independent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0008] The invention relates to a method for determining the spark duration during the operation of an ignition device for an internal combustion engine with a spark plug and an ignition coil with a primary winding (also referred to as the primary coil) and a secondary winding (also referred to as the secondary coil), as already mentioned above. Here, one ignition coil can be provided for several spark plugs, or—as is common for modern internal combustion engines—a separate ignition coil for each spark plug, which is then typically installed in a housing with the spark plug. Control (typically via a power stage) is generally effected by a corresponding processing unit, e.g., an engine control unit.

[0009] To generate a spark (in a classic coil ignition system), the ignition coil, or rather its primary winding, can be charged to a predetermined current or current value. During the charging process, the current increases from zero. At the desired ignition point, the current flow through the primary winding is interrupted, causing an oscillation in the secondary winding. This oscillation increases the secondary voltage (i.e., the voltage in the secondary winding) until breakdown occurs at the spark plug. The energy of the ignition coil is then discharged on the secondary side by driving the spark current (i.e., the current flowing across the spark gap) for a certain duration, which depends on the primary current (i.e., the current to which the primary winding was charged). The spark current decreases continuously until the spark extinguishes.

[0010] To detect faults in or around the ignition system, the spark duration can be determined by measuring the voltage feedback from the secondary winding to the primary winding. During the spark, the voltage at the collector of a driving stage is slightly higher than the supplying battery voltage. This voltage increase can be digitized using a voltage comparator, allowing the duration of this signal to be measured. An excessively short spark duration, for example, indicates potential ignition misfires. However, a disadvantage of this method is the need for a complex measurement of the (superimposed) voltage at the primary winding.

[0011] Another way to detect faults is to monitor the current flow or current profile in the primary winding during charging, for example, via a shunt in the primary winding circuit. This allows conclusions to be drawn about electrical faults in the primary winding (short circuit or open circuit). This method can therefore be used to suspend the ignition coil's control in the event of a fault, thus protecting the output stage. However, it cannot detect faults in the spark plug itself.

[0012] Against this background, the proposed method now determines the spark burning duration based on a subsequent spark ignition with a preferably shortened or minimal reloading time.

[0013] As with a conventional follow-up spark ignition system, the primary winding is first charged in an initial charging cycle. Then, at the desired ignition point, the current flow in the primary winding is interrupted. Subsequently, in one or more recharging cycles, the primary winding is recharged, extinguishing the ignition spark. During the recharging cycle, current flows into the primary coil for a certain period, which is then interrupted again for another ignition. A recharging cycle is preferably initiated before an ignition spark has extinguished.

[0014] As long as residual energy remains in the field of the ignition coil, the current during recharging processes does not start from zero, but jumps to an initial value that depends on the currently available residual energy.

[0015] The spark duration can now be easily determined if, during the successive spark ignition while charging the primary winding, a current flow through the primary winding is detected at least during one of the recharging cycles, for example, using the shunt mentioned above. As explained, the initial value of the current flow depends on the residual energy currently present. Therefore, as long as the initial value for a (specific) recharging cycle is above a predetermined threshold, e.g., 50 mA, there is still enough residual energy in the coil, and it can be assumed that the spark is still burning. If, on the other hand, the initial value is below the predetermined threshold (and thus almost zero), it can be assumed that the spark has extinguished.Then, based on the time period between the interruption of the current flow in the primary winding after the initial charging process and this recharging process, the spark duration is determined; in particular, this time period is defined as the spark duration.

[0016] The measuring method according to the invention can be used both selectively to measure the spark duration as needed or regularly. It can also be used in situations where a subsequent spark ignition occurs anyway, e.g., at low speeds, where the spark is then interrupted by the recharging process.

[0017] Especially when the measurement method is to be used in situations where no subsequent spark ignition occurs, it is advantageous if the influence of the measurement on the ignition is minimal. By reducing the recharge time, i.e., the duration of the recharge cycles, to very small values ​​(e.g., less than 50 µs or approximately 20 µs), the (noticeable) recharge of energy and thus the (unwanted) extension of the spark duration can be avoided. Then, the initial value of the current flow in the primary winding essentially corresponds (only) to that caused by the residual energy of the initial charge of the ignition coil. Therefore, if the initial current during a recharge cycle is zero or at least below the specified threshold during a sampling or measurement, it can be assumed that the spark has extinguished. This allows the spark duration to be determined.

[0018] The duration of the spark plug's burn time can be used to determine its functionality, including its condition (e.g., any contamination and / or aging), as well as the functionality of the primary and / or secondary windings. Conversely, it can also indicate a fault in the spark plug, primary winding, or secondary winding. If a fault is detected, a fault response is initiated, for example, to protect a control stage.

[0019] A computing unit according to the invention, e.g. a control unit of a motor vehicle, is, in particular in terms of programming, equipped to carry out a method according to the invention.

[0020] Implementing a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, as this incurs particularly low costs, especially if an executing control unit is already available for other tasks. Suitable data carriers for providing the computer program are, in particular, magnetic, optical, and electrical storage media, such as hard drives, flash memory, EEPROMs, DVDs, etc. Downloading a program via computer networks (Internet, intranet, etc.) is also possible.

[0021] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0022] The invention is schematically illustrated in the drawing using an exemplary embodiment and is described below with reference to the drawing. Brief description of the drawings Fig. Figure 1 schematically shows an ignition device in which a method according to the invention can be carried out. Fig. Figure 2 schematically shows the voltage and current curves for a conventional follow-up spark ignition. Fig. Figure 3 schematically shows a current flow in the primary winding in a preferred embodiment of a method according to the invention. embodiment(s) of the invention

[0023] In Fig. Figure 1 schematically depicts an ignition device 110 for an internal combustion engine 100, in which a method according to the invention can be carried out. The ignition device 110 has an ignition coil 120 with a primary winding 121 and a secondary winding 122.

[0024] The primary winding is connected to a power stage 106 of a computing unit 105 designed as a motor control unit. Current flow in the primary winding 121 can be detected, for example, by a current sensor 107 (e.g., by measuring a voltage drop across a shunt resistor), which can also be integrated into the motor control unit 105. The power stage can also be integrated with the coil, in which case the output of the motor control unit drives the power stage on the coil. The shunt could also then be integrated into the coil, and the measurement result would be sent to the motor control unit via an interface.

[0025] The secondary winding 122 is connected to ground at one end, the other end leads to a spark plug 130, which in turn is located in an internal combustion engine, specifically in a combustion chamber. This representation is only schematic, and the ignition coil can, as already mentioned, also be located in a housing that accommodates the spark plug.

[0026] In Fig. Figure 2 shows schematic diagrams of the voltage U and current I across the primary winding of the ignition coil over a time t in a conventional follow-up spark ignition system. The voltage U, as applied to the primary winding by the output stage, initially generates an increasing current, which drops when the ignition is interrupted, causing a voltage increase in the secondary winding and thus generating a spark.

[0027] The primary winding is then recharged before the spark has extinguished. Due to the residual energy in the ignition coil's field, the current does not rise from zero, but jumps to an initial value that depends on the residual energy remaining in the ignition coil and decreases slightly with each recharge cycle, as can be seen, which is due to the recharge strategy used.

[0028] In Fig. Figure 3 schematically shows the current I in the primary winding over time t in a preferred embodiment of a method according to the invention. The basic curve corresponds to that shown in Fig. 2. Course of the current shown.

[0029] At time t0, the initial charging process EL begins, during which the primary winding is charged. At time t1, the current flow in the primary winding is interrupted, thus ending the initial charging process. Subsequently, the primary winding is recharged several times, for example at times t2, t3, t4, t5, and t6, in recharging processes NL, each time for a very short duration, e.g., approximately 20 µs, after which the current flow is interrupted again.

[0030] Here too, the current decreases with each recharging process; however, due to the very short recharging times, the current measured in each instance corresponds to a value that depends on the remaining energy and thus on the instantaneous spark current. As soon as the current during a recharging process is zero, or at least below a certain threshold I, S If the spark has died, it can be assumed that the spark has gone out.

[0031] The spark duration Δt is thus derived from the time between the initial interruption of the current flow in the primary winding at time t1 and time t6 of the respective recharging process. Based on this spark duration, faults in the spark plug or in the primary winding can then be detected.

Claims

[1] Method for determining a spark duration (Δt) during the operation of an ignition device (110) for an internal combustion engine (100) with a spark plug (130) and an ignition coil (120) with primary winding (121) and secondary winding (122), wherein for an ignition process, first, in an initial charging process (EL), the primary winding (121) is charged and a current flow in the primary winding (121) is interrupted, and subsequently, once or several times, in recharging processes (NL), the primary winding (122) is recharged and the current flow is interrupted, wherein during a charging of the primary winding (122) at least during one of the recharging processes (NL) a current flow (I) through the primary winding (121) is detected, and where, if an initial value of the current flow (I) through the primary winding (121) for the recharging process (NL) is below a predetermined threshold value (I S) is based on the time period between the interruption of the current flow in the primary winding (121) after the initial charging process (EL) and this recharging process (NL) the spark duration (Δt) is determined. [2] Method according to claim 1, wherein the time period between the interruption of the current flow (I) in the primary winding (121) after the initial charging process (EL) and this recharging process (NL) is determined as the spark duration (Δt). [3] Method according to claim 1 or 2, wherein in the recharging processes (NL) the primary winding (121) is charged for a predetermined period of time, which preferably is at most 50 µs. [4] Method according to one of the preceding claims, wherein a recharging process (NL) is started each time before an ignition spark has been extinguished. [5] Method according to one of the preceding claims, wherein the functionality of the spark plug (130) is inferred from the determined spark duration (Δt). [6] Method according to one of the preceding claims, wherein the functionality of the primary winding (121) and / or the secondary winding (122) is determined based on the specified spark duration (Δt). [7] Method according to claim 5 or 6, wherein, if it is concluded that functionality is not present, a fault response is initiated. [8] Computing unit (105) which is configured to perform all the process steps of a process according to any of the preceding claims. [9] Computer program that causes a computing unit (105) to perform all the process steps of a method according to any one of claims 1 to 7 when executed on the computing unit (105). [10] Machine-readable storage medium with a computer program stored thereon according to claim 9.

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