JP2010138880A - Combustion control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combustion control device capable of realizing appropriate ignition control by detecting at an early stage whether ignition is realized or not in a multi-ignition method. <P>SOLUTION: This combustion control device includes: an ignition transformer T comprising a primary coil L1 and a secondary coil L2 electromagnetically connected with each other; a switching element Q for controlling ON/OFF of an electric current of the primary coil L1 a plurality of times in one ignition cycle; an ignition plug PG for performing spark discharge by receiving high pressure voltage induced by the secondary coil L2; a signal detecting part for detecting a secondary current and secondary voltage of the ignition transformer T; a level determining part (ST4) for determining whether or not a detection value detected by the detecting part exceeds a determination level in a capacity discharge section; and combustion determining parts (ST6, ST7) for determining the combustion state of a combustion chamber based on output of the level determining part (ST4). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a combustion control apparatus capable of detecting a combustion state at a quick timing in an internal combustion engine adopting a multiple ignition system, and enabling an appropriate control operation based on the detection result.

  In an internal combustion engine such as an automobile engine, an air / fuel mixture introduced into a combustion chamber is burned by ignition discharge of an ignition plug to generate energy. In such an internal combustion engine, a multiple ignition system is known in which a spark plug is discharged a plurality of times in one ignition cycle. In this multiple ignition method, by repeating the discharge operation a plurality of times intermittently, for example, the ignition operation can be stabilized even when the air-fuel ratio of the air-fuel mixture is lean or in a large amount of exhaust gas recirculation (EGR).

  However, in the multiple ignition system, there is a problem that the ignition plug and the ignition transformer that supplies a high voltage to the ignition plug are severely deteriorated as much as the discharge operation is executed a plurality of times in one ignition cycle. In the multiple ignition method, there is also an energy waste that repeats unnecessary discharge operations even when the air-fuel mixture is stably combusting.

  The present invention has been made in view of the above-described problems, and provides a combustion control device that can detect whether ignition has been realized at an early stage in the multiple ignition system and realize appropriate ignition control. The issue is to provide.

  In order to solve the above problems, the present invention provides an ignition transformer in which a primary coil and a secondary coil are electromagnetically coupled, and a switching element that controls ON / OFF of the current of the primary coil a plurality of times during one ignition cycle. An ignition plug that receives a high voltage induced in the secondary coil and sparks in the combustion chamber, a signal detection unit that detects a current and / or voltage of the ignition transformer, and the detection unit detects A level determination unit that determines whether a detected value of current and / or voltage exceeds a determination level in a capacity discharge section, and a combustion determination that determines the combustion state of the combustion chamber based on the output of the level determination unit And a portion. Exceeding the judgment level includes not only the case where the judgment level is exceeded but also the case where the judgment level is below the judgment level depending on the positive / negative level of the detection value. It means exceeding.

  In the present invention, the capacity discharge section means a section from when the spark plug is dielectrically broken until the secondary voltage of the ignition transformer finishes abruptly decreasing. In general, in this type of ignition circuit, as shown in FIG. 1A, when the secondary voltage of the ignition transformer reaches the breakdown voltage of the ignition plug, the electrostatic energy charged in the stray capacity until then is released at once. As a result, the secondary voltage drops rapidly (capacitive discharge), and the subsequent inductive discharge is continued.

  Based on the above, the present inventor has carefully examined the voltage waveform and current waveform of each part of the ignition transformer while repeatedly discharging the ignition plug. It was found that there was a significant difference immediately after dielectric breakdown of the spark plug.

  That is, according to the examination result of the present inventors, in the multiple ignition method, after the combustion is started, the primary voltage, secondary voltage, and secondary voltage of the ignition transformer in the capacity discharge section immediately after the dielectric breakdown are more than before. The secondary current was found to be significantly lower. In relation to this phenomenon, a binary signal (determination pulse) obtained by comparing the primary voltage, secondary voltage, or secondary current with a predetermined determination level (threshold) is also used after combustion is started. Has a narrower pulse width than before.

  Therefore, according to the configuration of the present invention, whether or not current or voltage exceeding the determination level is detected in the capacity discharge section by setting the determination level in the level determination unit to a relatively high appropriate value. Based on this, the combustion state can be detected. Alternatively, by setting the determination level in the level determination unit to a slightly lower appropriate value, the combustion state is determined based on whether or not the pulse width of the determination pulse indicating that the determination level is exceeded is narrower than the reference value. Can be detected.

  Note that the comparison processing with the determination level may be performed in the state of an analog signal as shown in FIG. 1A, or after the analog signal is converted into a digital signal as shown in FIG. Also good. In the former case, there is an advantage that high-speed processing is possible, and in the latter case, complicated and advanced comparison processing is possible.

  As described above, in the simplest case, when a current or voltage exceeding the determination level is not detected, it can be determined that the combustion state is present. This determination is preferably based on temporal transition, for example, until then, detection signals exceeding the determination level were continuously detected, but in the subsequent capacity discharge section, detection signals exceeding the determination level were detected. When it is no longer detected, it can be determined that combustion has started. Conversely, if a detection signal exceeding the determination level has not been detected so far, but a detection signal exceeding the determination level is detected in the subsequent capacity discharge section, it may be determined that a misfire state has been reached. it can.

  In any case, in such an embodiment, the level determination unit can be configured by an analog circuit, and can be processed quickly in real time within one ignition cycle without applying a control load to the computer circuit. It becomes. And when a combustion determination part determines with combustion having started reliably, the drive of a subsequent ignition coil can be stopped, for example. On the contrary, when the combustion determination unit determines that the misfire state is present, for example, it is possible to take measures to adjust the supply amount of the air-fuel mixture and the air fuel consumption.

  In the present invention, in order to increase the determination accuracy, the determination parameter calculated from the temporal transition of the voltage value or the current value is used instead of relying only on the level determination of the voltage peak value or the current peak value in the capacity discharge section. It is desirable to consider. For example, the combustion determination unit performs combustion based on one or more of the accumulated time of the excess section where the detected voltage exceeds the voltage determination level, the accumulated value of the detected voltage in the excess section, or the peak value of the detected voltage in the excess section. It is preferable to determine the state.

  Here, the excess section means the pulse width of the binary signal indicating that the detection signal exceeds the determination level. In the combustion state, the pulse width is narrower than that in the misfire state. Can be increased. Moreover, determination accuracy is further increased by evaluating a combination of a plurality of determination parameters.

  Similarly, in the combustion determination unit, based on one or more of the accumulated time of the excess section where the detected current exceeds the current determination level, the accumulated value of the detected current in the excess section, or the peak value of the detected current in the excess section. It is also preferable to determine the combustion state.

  Furthermore, the signal detection unit detects a detection voltage that is a primary side voltage or a secondary side voltage of the ignition transformer together with the secondary side current of the ignition transformer, and the combustion determination unit exceeds the detection voltage exceeding the voltage determination level. It is also effective to determine the combustion state based on the calculation result of the detected voltage and the secondary current in the section.

  Similarly, the signal detection unit detects a detection voltage which is the primary side voltage or the secondary side voltage of the ignition transformer together with the secondary side current of the ignition transformer, and the combustion side determination unit detects the current determination level of the secondary side current. It is also effective to determine the combustion state based on the calculation result of the detected voltage and the secondary current in the excess section. In any of the above cases, the calculation is preferably exemplified by an integration calculation that integrates the detection voltage and the secondary current.

  In addition, since combustion has not started until the first OFF transition of the switching element in one ignition cycle, the current value and voltage value of each part of the ignition transformer after the first OFF transition are almost significant. There is no difference. Therefore, it is effective that the combustion determination unit determines the combustion state based on the current value and / or the voltage value after the second OFF transition of the switching element during one ignition cycle.

  By the way, the state of the primary voltage, secondary voltage, or secondary current of the ignition transformer changes depending on the plug gap and the plug shape of the spark plug, so the determination level used in the level determination unit depends on the secular change of the spark plug, etc. Corresponding modifications should be made accordingly. Specifically, the computer circuit is equipped with a learning function that sequentially corrects the determination level by verifying whether the combustion determination using the determination level in the initial state is correct or not based on information from other sensors and detection circuits. Is preferred.

  According to the above-described combustion control device of the present invention, since the combustion state can be grasped at an early stage, unnecessary ignition operation can be suppressed, and the life of the spark plug and the ignition coil can be increased. Moreover, since stable lean combustion, large-volume EGR combustion, and the like can be realized, fuel consumption can be improved and environmental pollution can be prevented.

  Examples of the present invention will be described below. FIG. 2A illustrates a circuit configuration used in the basic experiment.

  The combustion control device shown in the figure is induced by an ignition transformer T in which a primary coil L1 and a secondary coil L2 are electromagnetically coupled, a switching element Q for ON / OFF control of the current of the primary coil L1, and a secondary coil L2. Spark plug PG that receives a high voltage and sparks in the combustion chamber, AD converters ADC1 and ADC2 that receive analog detection signals corresponding to secondary current I2 and secondary voltage V2 of ignition transformer T, and AD converter ADC1 , And a computer circuit COM that receives the digital detection signal from the ADC 2 and drives the switching element Q.

  In this combustion control device, a multiple ignition method is employed in which the discharge operation is repeated a plurality of times during one ignition cycle. That is, the computer circuit COM repeatedly supplies the ignition pulse SG to the gate terminal of the switching element (IGBT) Q a plurality of times during one ignition cycle. Although not particularly limited, the ignition pulse SG has a pulse period of about 200 μS to 400 μS, and its duty ratio is about 35% to 65%.

  As illustrated, the secondary voltage V2 supplied to the spark plug PG is supplied to the computer circuit COM via the step-down circuit DP and the AD converter ADC1. The secondary current I2 flowing through the secondary coil L2 is converted into a voltage across the shunt resistor RS, and then supplied to the computer circuit COM via the AD converter ADC2. In this embodiment, the level determination unit that determines whether or not the detection signal exceeds the determination level in the capacity discharge section, and the combustion determination unit that determines the combustion state based on the output of the level determination unit are both computers. The circuit COM is configured.

  In addition, the computer circuit COM operates the AD converter in the capacity discharge section to acquire a detection signal, while in the subsequent induction discharge section, performs combustion determination and combustion control based on the acquired detection signal. (See FIG. 2 (b)). The sampling period of the AD converter is preferably as short as possible. However, in order to realize precise combustion determination, for example, it is preferable to operate at about 0.1 μS.

  However, the AD converter is not necessarily essential. For example, as shown in FIG. 1B, a comparator that receives an analog detection signal and a reference voltage and outputs a binary signal may be used. In such a configuration, the peak value of the secondary voltage or secondary current cannot be acquired, but the pulse width of the binary signal indicating that the detection signal exceeds the reference voltage can be evaluated. The combustion state can be detected.

  The primary coil L1 and the secondary coil L2 constituting the ignition transformer T have coil windings wound in the same phase. Therefore, when the switching element Q is turned OFF and the current of the primary coil L1 is cut off, a high voltage in the direction shown in the figure is induced in the secondary coil L2. This induced voltage charges the stray capacitance C almost instantaneously. However, when the high voltage applied to the spark plug PG exceeds its breakdown voltage, the electrostatic energy charged in the stray capacitance C is instantaneously released. Capacitive discharge is performed. And after a secondary voltage falls to about several hundred volts by capacitive discharge, inductive discharge is continued.

  FIG. 3 is a time chart showing the relationship between the secondary voltage V2 of the ignition transformer T and the ignition pulse SG. FIG. 3B shows a combustion state in which the combustion started at the first falling edge of the ignition pulse SG is maintained thereafter. On the other hand, FIG. 3C shows a state where the air-fuel mixture is not combusted consistently regardless of the spark discharge of the spark plug PG.

  FIG. 4 is a time chart showing the relationship between the secondary current I2 of the ignition transformer T and the ignition pulse SG. As in the case of FIG. 3, the combustion state is consistent with the consistent combustion state (FIG. 4B). The misfire state (FIG. 4C) is shown. In this embodiment, the ignition pulse SG is repeatedly and intermittently supplied to the switching element Q at a pulse period τ (≈280 μS) after the first falling edge. The duty ratio is about 60%.

  As shown in FIGS. 3B and 3C, the voltage peak value of the secondary voltage V2 in the capacitive discharge section after the falling edge of the ignition pulse SG is significantly deeper at the time of misfire than at the time of combustion. Similarly, for the secondary current, the current peak value is significantly deeper during misfire than during combustion. 4B and 4C, the scale of the vertical axis is different, but the threshold value TH is the same value.

  As confirmed from FIGS. 3 to 4, the voltage peak value and the current peak value are significantly different between combustion and misfire. For example, if the determination threshold TH is appropriately set, the determination exceeds the determination threshold TH. Whether there is a misfire state or a combustion state can be determined based on whether a voltage peak or a current peak exists.

  If the combustion state is determined based on the accumulated time Wj of the excess section where the detected voltage exceeds the determination threshold TH or the accumulated value Sj of the detected voltage in the excess section in consideration of the temporal transition of the voltage value and the current value. Judgment accuracy is improved. FIG. 5A shows the cumulative secondary voltage V2 for the excess section exceeding the determination threshold TH (cumulative value ΣSj). Here, since the secondary voltage V2 in the excess section is accumulated for each ignition cycle τ of the spark plug SG, a staircase wave shape increasing for each ignition cycle τ is shown. On the other hand, FIG. 5 (b) is obtained by accumulating the excess section Wj for each ignition cycle τ (cumulative value ΣWj), and has the same staircase shape as in FIG. 5 (a).

  As is clear from FIG. 5, based on the cumulative value ΣWj of the excess section and the cumulative value ΣSj of the voltage value and current value in the excess section, it is possible to specify the combustion state or the misfire state with high accuracy. For example, for a plurality of ignition operations in one ignition cycle, if a threshold value THj is provided for each ignition operation, reliable combustion is performed based on whether the threshold value THj is continuously exceeded or continuously reduced. Judgment can be made. The threshold value THj is a value related to the cumulative value ΣWj and / or the cumulative value ΣSj.

  However, it is also preferable to determine combustion based on the same threshold value TH during each ignition operation. In this case, for example, until the middle of multiple ignition, the determination parameter Sj and / or the determination parameter Wj continuously exceeded the respective threshold values THa and THb, but thereafter, the threshold values THa and THb were exceeded. If it falls below, it can be determined that combustion has started.

  FIG. 6 is a flowchart showing the operation content during one ignition cycle of the combustion control device mounted on the internal combustion engine. Here, the computer COM performs the combustion control based on the secondary voltage V2 output from the AD converter ADC1. In the following description, it is assumed that this is the jth time in the multiple ignition operation.

  In this case, the computer circuit COM first determines whether or not the j-th falling timing of the ignition pulse SG has been reached (ST1), and starts the operation of the AD converter ADC1 when the falling timing is reached. (ST2).

  When the AD conversion operation is completed, the AD-converted secondary voltage V2 is sequentially acquired as a variable DTi (ST3). As described above, in the present embodiment, the AD conversion process (ST2), the conversion data DTi acquisition process (ST3), and the amplification cycle are repeated (ST4) until the capacitive discharge ends with certainty.

  Here, the data acquisition section determined in the process of step ST4 is a section that is sufficiently wider than the capacity discharge section specified experimentally in advance, and is set to, for example, around 20 μS. In addition, the sampling period of the AD converter ADC1 is set to about 0.1 μS so that the peak value of the secondary voltage V2 can be reliably identified.

  As described above, when the data acquisition process for the capacity discharge section is completed, each acquired data DTi (i = 0 to N) is compared with the threshold value TH for level determination and exceeds the threshold value TH. The excess section Wj (j = 1, 2,...) Is specified and stored in the memory (ST5). Further, the value of the acquired data DTi included in the excess section is accumulated (Sj ← Sj + DTi), and the accumulated value Sj as the addition result is stored in the memory (ST5).

  Next, the current (= j-th) excess section Wj calculated in step ST5 and the cumulative value Sj are comprehensively evaluated together with past calculation results to make a combustion determination (ST6). Although the method of comprehensive evaluation is not particularly limited, typically, a cumulative value with past calculation results (S1, S2,... / W1, W2,...) Is calculated, and based on the calculation results. Make a combustion judgment.

  For example, when the cumulative value Sj of the acquired data in the excess section during each ignition operation is sequentially added (ΣSj), a significant difference occurs depending on whether or not the combustion state exists as shown in FIG. Further, even if the excess sections Wj at the time of each ignition operation are sequentially added (ΣWj), a significant difference as shown in FIG.

  Therefore, appropriate combustion control is performed based on the determination result based on such determination parameters (ΣSj, ΣWj), and the j-th operation is finished (ST7). Specifically, when it is determined that combustion has not started, measures such as adjusting the air-fuel ratio of the air-fuel mixture or adjusting the pulse width and duty ratio of the ignition pulse SG are taken and processed, for example. Finish. Note that the processes of steps ST1 to ST7 are repeated in the same manner as described above for the j + 1th and subsequent times in the multiple ignition operation.

  It should be noted that the threshold value TH for level determination used in the process of step ST5 is corrected as appropriate in accordance with replacement of the spark plug, aging, and the like. For example, an ion current detection circuit that detects ions generated in the combustion chamber during combustion on the secondary side of the ignition transformer is provided, and the combustion determination based on the detected ion current is compared with the combustion determination based on the threshold value TH. The threshold value TH is appropriately corrected to the optimum level.

  As mentioned above, although the Example of this invention was described in detail, the concrete description content does not specifically limit this invention. For example, in the embodiment, the case where combustion is determined based on the secondary voltage is illustrated, but it is needless to say that the primary voltage V1 and the secondary current I2 can be used instead of the secondary voltage V2. Further, it is possible to make a combustion determination based on a determination parameter obtained by appropriately combining a plurality of detection values such as the secondary voltage V2, the secondary current I2, and the primary voltage V1, and these composite determination parameters include V2 * I2 and V1. * Calculated values such as I2 are preferably exemplified.

It is drawing explaining the basic composition of the present invention. It is a circuit block diagram explaining the combustion control device concerning an example. It is a time chart which shows the ignition pulse and secondary voltage at the time of multiple discharge. It is a time chart which shows the ignition pulse and secondary current at the time of multiple discharge. It is drawing which shows that combustion and misfire can be discriminate | determined with a specific determination parameter. 3 is a flowchart for explaining a control operation of the computer circuit of FIG. 1.

Explanation of symbols

L1 Primary coil L2 Secondary coil T Ignition transformer Q Switching element PG Spark plug

Claims (7)

An ignition transformer in which a primary coil and a secondary coil are electromagnetically coupled;
A switching element for ON / OFF controlling the current of the primary coil a plurality of times during one ignition cycle;
A spark plug that receives a high voltage induced in the secondary coil and sparks in the combustion chamber;
A signal detector for detecting the current and / or voltage of the ignition transformer;
A level determination unit that determines whether the detected value of the current and / or voltage detected by the detection unit exceeds a determination level in a capacity discharge section;
A combustion determination unit that determines the combustion state of the combustion chamber based on the output of the level determination unit;
A combustion control apparatus for an internal combustion engine, characterized by comprising:   The combustion control device according to claim 1, wherein the combustion determination unit determines a combustion state based on a current value and / or a voltage value in a time interval in which the detected value exceeds a determination level. The signal detection unit detects a detection voltage that is a primary side voltage or a secondary side voltage of the ignition transformer,
In the combustion determination unit, any one or more of the accumulated time of the excess section where the detected voltage exceeds the voltage determination level, the accumulated value of the detected voltage in the excess section, or the peak value of the detected voltage in the excess section The combustion control device according to claim 1, wherein the combustion state is determined based on the above. The signal detection unit detects a detection current which is a primary side current or a secondary side current of the ignition transformer,
In the combustion determination unit, any one or more of the accumulated time of the excess section where the detected current exceeds the current determination level, the accumulated value of the detected current in the excess section, or the peak value of the detected current in the excess section The combustion control device according to claim 1, wherein the combustion state is determined based on the above. The signal detection unit detects a detection voltage that is a primary side voltage or a secondary side voltage of the ignition transformer together with a secondary side current of the ignition transformer,
The combustion control according to claim 1 or 2, wherein the combustion determination unit determines a combustion state based on a calculation result of the detection voltage and the secondary current in an excess section where the detection voltage exceeds a voltage determination level. apparatus. The signal detection unit detects a detection voltage that is a primary side voltage or a secondary side voltage of the ignition transformer together with a secondary side current of the ignition transformer,
The combustion determination unit according to claim 1 or 2, wherein the combustion determination unit determines a combustion state based on a calculation result of the detection voltage and the secondary side current in an excess section where the secondary side current exceeds a current determination level. Combustion control device.   The said combustion determination part determines a combustion state based on the electric current value and / or voltage value after the second OFF transition of the said switching element in one ignition cycle. Combustion control device.

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