JP5560437B2 - Combustion control device for internal combustion engine - Google Patents

Description

  The present invention relates to a combustion control apparatus that optimizes combustion control at start-up in an internal combustion engine such as an automobile engine.

  Suppressing air pollution by automobiles is a global problem, and as a part of that, it is required to mount OBD (On Board Diagnosis) on automobiles. OBD means a vehicle-mounted fault diagnosis system. For example, when an abnormality occurs in a three-way catalyst or the like and the amount of harmful gas in the exhaust gas exceeds the OBD regulation value, a warning lamp is turned on to notify the driver. Thus, steady suppression of air pollution is achieved (Patent Document 1).

JP 2007-327351 A

However, at the time of cold start, since the three-way catalyst or the O ₂ sensor does not function effectively, there is a problem that it is not easy to realize an optimum operation that satisfies the OBD regulation value.

  That is, if the air-fuel ratio (A / F) is too lean during cold start, combustion deteriorates and start-up performance is significantly deteriorated, and unburned gas such as HC (Hydro Carbon) also increases. For this reason, the air-fuel ratio is excessively controlled to the rich side, but the fuel efficiency is deteriorated by that amount, and unburned gas is also generated.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a combustion control device that can realize optimal air-fuel ratio control during cold start.

  In order to achieve the above object, the present inventor has repeatedly controlled the combustion state by controlling the air-fuel ratio to the lean side and measuring the cylinder pressure of the internal combustion engine with a pressure sensor. As a result, at the time of critical lean combustion, there are a mixture of cases where normal output cannot be obtained due to poor combustion and cases where normal output can be obtained, and (2) ions generated in the internal combustion engine Focusing on the behavior of the current, it became clear that the combustion failure state at the time of lean combustion can be specified without using a pressure sensor.

The present invention is based on the above-described knowledge. In general, an ignition coil having a primary coil and a secondary coil, a switching element for controlling energization of the primary coil, and turning on / off the switching element. A control device that operates and performs air-fuel ratio control at the time of cold start, an ignition plug that performs ignition discharge in response to an induced voltage of the secondary coil generated in response to a transition operation of the switching element, and the ignition And a signal detecting circuit for detecting a current signal passing through the plug, and determining means for determining whether or not the combustion operation of the internal combustion engine is appropriate based on the current signal acquired at the time of air-fuel ratio control If, when the combustion operation by the determining means is determined to be proper, while advancing the air-fuel ratio leaner in subsequent ignition cycle, when it is determined not to be appropriate And changing means in the subsequent ignition cycle take recovery measures to improve combustion, but it is configured to function at cold start. Hereinafter, the contents of the reference technique not included in the scope of the present invention will be described with reference to FIGS.

  FIG. 1 illustrates an ion current detection signal Vo (hereinafter abbreviated as ion current Vo) when the air-fuel ratio is controlled to the lean side in the combustion control apparatus DET shown in FIG. Here, in the case where the internal combustion engine is operated at an air-fuel ratio A / F = 14.5 (FIG. 1 (a)) and the case where it is operated at an air-fuel ratio A / F = 17 (FIG. 1 (b)) Shows a typical waveform. In the circuit configuration of FIG. 7, the ignition pulse SG falls at the timing T0, and a high voltage is applied to the spark plug PG.

  Regardless of the air-fuel ratio, an LC oscillation section (discharge noise section) occurs after ignition discharge of the spark plug PG. When the peak position PK of the ion current Vo is evaluated except for this LC oscillation section, when lean combustion is performed. It is confirmed that the peak position PK is significantly delayed. Note that the end of the LC vibration section is simply determined by the elapsed time from the falling timing T0 of the ignition pulse SG. However, the determination may be made on the basis that the vibration period of the LC vibration wave is significantly different from the period of the ion current.

  When the peak position PK after the LC oscillation interval of the ionic current Vo is evaluated by the elapsed time τ from the ignition timing T0, the elapsed time τ is directly related to the air-fuel ratio A / F as shown in FIG. Confirmed to be related. FIG. 1C shows ion currents in a plurality of ignition cycles for five groups (A / F = 12, 14, 15.5, 16, 17) having different target values of the air-fuel ratio A / F. The elapsed time τ to the peak position PK of Vo is plotted. The elapsed time τ is the elapsed time from the ignition timing T0, and the air-fuel ratio at the plot position is the air-fuel ratio specified from the A / F sensor.

  Here, all the cases where the elapsed time τ to the peak position PK exceeds 12 mS belong to the group having the target air-fuel ratio of 17. However, as shown in FIG. 1C, for example, even if the air-fuel ratio is around 17, the elapsed time τ to the peak position PK is not uniform, and it is confirmed that the peak position PK varies greatly. .

  When the variation in the peak position PK was examined in comparison with the in-cylinder pressure measured in parallel with the ion current Vo, the combustion failure group having a low in-cylinder pressure had an elapsed time τ to the peak position of about 8 mS or more. (See FIGS. 2 (a) and 2 (b)). Therefore, the quality of combustion during lean combustion can be determined in real time by using the peak position PK of the ion current as a determination parameter. The peak position PK does not necessarily have to be based on the ignition timing T0, and may be based on a 0DC (Crank Angle) TDC (Top Dead Center).

  In any case, if it is determined that the combustion is poor, recovery measures may be taken to improve combustion. As recovery measures, for example, (a) the air-fuel ratio is changed to the fuel rich side to mitigate lean combustion, (b) the energization time of the primary coil is lengthened and ignition energy is increased, (c) ignition timing T0. Measures such as changing can be considered.

  By the way, when paying attention to the correlation diagram of FIG. 2B, even if the elapsed time τ to the peak position PK is short, there is a case where the in-cylinder pressure PR is low (see arrow), and detection failure may occur with respect to the combustion failure. Showing sex. Then, as a result of further examination, it became clear that a combustion failure can be detected with higher accuracy by determining a so-called afterburning section.

  FIG. 3A is a plot of the time integral value ITG obtained by accumulating the ion current Vo from 100 CA to 360 CA after the ignition timing T0 in relation to the air-fuel ratio A / F specified from the A / F sensor. is there. Similar to the case of FIG. 2, the time integration value ITG is not uniform even when the air-fuel ratio is around 17.

  FIG. 3B is a plot of the relationship between the time integrated value ITG and the air-fuel ratio A / F for only the measurement group in which the target air-fuel ratio A / F is 17. On the other hand, FIG. 3C is a plot of the in-cylinder pressure PR measured in parallel with the ion current Vo for the measurement group with the target air-fuel ratio A / F of 17 in relation to the time integral value ITG. . Here, it is confirmed that the combustion failure group having a low in-cylinder pressure matches the group having a large time integration value ITG.

  Therefore, the combustion failure state can be detected with high accuracy by analyzing the behavior of the subsequent region (for example, 100 to 360 CA) of the ion current Vo during lean combustion.

  Next, the present inventor has also studied various other determination parameters that can specify the combustion failure state with high accuracy. As a result, the ion current Vo is accumulated from the ignition timing T0 until the ion current surely disappears (360 CA) to calculate the total integral value TOTAL, and until the time integral value reaches a predetermined ratio of the total integral value TOTAL. It became clear that the elapsed time was also an effective determination parameter. In this case as well, the calculation base point of the total integral value TOTAL is not limited to the ignition timing T0 but may be TDC.

  FIG. 4A shows a time integrated value TOTAL of the entire region (T0 to 360CA) of the ion current Vo for a measurement group having a target air-fuel ratio A / F of 17, and a 50% level of the total integrated value TOTAL. The elapsed time τ ′ (50% position) until reaching (= TOTAL / 2) is illustrated. Also in this case, the in-cylinder pressure PR is measured in parallel, and FIG. 4B shows the relationship between the 50% position τ ′ and the in-cylinder pressure PR. Also in this combustion experiment, the combustion failure group with a low in-cylinder pressure PR coincided with the failure group with a large 50% position τ '. Therefore, the combustion failure state can be detected with high accuracy by using the 50% position as a determination parameter.

  Further, in order to more effectively detect the post-burning state, for example, it is also effective to compare the behavior of the former region of the ion current Vo with the behavior of the latter region. For example, the behavior of the front region is specified by the cumulative value (time integration value) of the ion current Vo from the ignition timing T0 to 100 CA, and the behavior of the rear region is specified by the cumulative value of the ion current Vo from 100 CA to 360 CA. The Note that the boundary position between the front and rear stages is not limited to 100 CA, and is set to an optimum value experimentally.

  As shown in FIG. 5 (a), in general, the lower the air-fuel ratio A / F and the worse the combustion, the smaller the initial combustion and the larger the afterburning. For this reason, the worse the combustion, the larger the time integral value in the rear region, while the smaller the time integral value in the front region.

  Therefore, for example, it is effective to use [time integrated value of the subsequent region] / [time integrated value of the previous region] as a determination parameter. FIG. 5B illustrates the relationship between the area ratio S of the time integral value and the measured air-fuel ratio A / F, with the ignition timing T0 to 100CA as the front stage and the 100CA to 360CA as the rear stage region. The larger the area ratio S, the more remarkable the tendency of afterburning.

  FIG. 5C illustrates the relationship between the in-cylinder pressure PR and the area ratio S measured in parallel for the same measurement group. Also in this combustion experiment, the poor combustion group having a low in-cylinder pressure PR coincided with a group having a large after-burning tendency and a large area ratio S. Therefore, it is also effective to use the area ratio of the time integral value as a determination parameter.

  Further, instead of making a determination based on a real-time value acquired in each ignition cycle, it is also preferable to use a statistical value obtained by integrating the acquired values in a plurality of ignition cycles as a determination parameter. As the statistical value, for the above-described determination parameter (for example, 50% position τ ′), a moving average, a standard deviation, a variation rate (= standard deviation / moving average), etc. in a plurality of ignition cycles can be exemplified. FIG. 6 illustrates the relationship between the air / fuel ratio A / F and the 50% position fluctuation rate VAR (= standard deviation / moving average) for the measurement group with a target air / fuel ratio of 17. Also in this case, when the fluctuation rate VAR exceeds a predetermined value, it can be determined that the combustion is insufficient and the engine output is insufficient.

  According to the present invention described above, it is possible to realize a combustion control device with improved start characteristics by realizing optimal air-fuel ratio control during cold start without using a pressure sensor or the like.

It is drawing explaining the general ion waveform at the time of lean combustion. It is drawing which shows that the peak position of an ion waveform shifts when the air-fuel ratio is changed. It is drawing which shows the relationship between an air fuel ratio, the integrated value of an ion waveform, and a cylinder pressure. It is drawing which shows the correlation with an air fuel ratio and the 50% position of the total integral value of an ion waveform. It is drawing which shows the correlation with an air-fuel ratio, the integration ratio of a front-and-rear stage, and a cylinder pressure. It is drawing which shows the relationship between the fluctuation rate computed from a statistical value, and an air fuel ratio. It is a circuit diagram which shows the structure of the combustion control apparatus used in an Example. It is a time chart explaining operation | movement of a combustion control apparatus. It is a flowchart of the 1st Example explaining air-fuel-ratio control at the time of cold start. It is a flowchart of the 2nd Example explaining air-fuel-ratio control at the time of cold start.

  Hereinafter, the present invention will be described in more detail based on examples. FIG. 7 is a circuit diagram showing the combustion control device DET according to the embodiment, and FIG. 8 is a time chart showing schematic waveforms of each part of the combustion control device DET.

  As shown in FIG. 7, this combustion control device DET includes an ECU (Engine Control Unit) which is an electronic control unit of an internal combustion engine, an ignition coil CL composed of a primary coil L1 and a secondary coil L2, and an ignition pulse SG received from the ECU. The switching element Q that controls ON / OFF of the current ic1 of the primary coil L1 by the transition operation based on the ignition plug PG that receives the induced voltage of the secondary coil L2 and discharges, and the ion current detection circuit ION. It is configured. The output voltage Vo of the ionic current detection circuit ION is supplied to an A / D converter (not shown) of the ECU, and is stored in a memory of the ECU as a digital level detection signal.

  Hereinafter, the circuit configuration will be described in detail. As the switching element Q, here, an IGBT (Insulated Gate Bipolar Transistor) is used. The collector terminal of the switching element Q receives the battery voltage VB via the primary coil L1, and the emitter terminal is connected to the ground.

  The ion current detection circuit ION is mainly configured by an OP amplifier AMP that functions as a current detection circuit, and includes a capacitor C1, a Zener diode ZD, diodes D1 and D2, and resistors R1 to R3. A bias circuit at the time of ion current detection is generated by a parallel circuit of the capacitor C1 and the Zener diode ZD.

  The high voltage terminal of the secondary coil L2 is connected to the spark plug PG, and the low voltage terminal is connected to a parallel circuit of the capacitor C1 and the Zener diode ZD that generate the bias voltage. The parallel circuit of the capacitor C1 and the Zener diode ZD is connected to the ground through the diode D1. As illustrated, the cathode terminal of the diode D1 is connected to the ground.

  On the other hand, the anode terminal of the diode D1 is connected to the inverting input terminal (−) of the OP amplifier via the current limiting resistor R1. A current detection resistor R2 is connected between the inverting input terminal (−) and the output terminal of the OP amplifier AMP, and a load resistor R3 is connected between the grounds of the output terminals. The non-inverting terminal (+) of the OP amplifier is connected to the ground, and the cathode terminal of the diode D2 is connected to the inverting terminal (−). The anode terminal of the diode D2 is connected to the ground.

  In the combustion control apparatus DET having the above-described configuration, when the ignition pulse SG changes from the H level to the L level at the timing T0, the ignition plug PG is discharged by the high voltage induced in the secondary coil L2. Since this discharge current flows through the path of the spark plug PG → secondary coil L2 → capacitor C1 → diode D1, the capacitor C1 is charged to a voltage value defined by the breakdown voltage of the Zener diode ZD.

  When the LC oscillation is started by the discharge of the spark plug PG and the air-fuel mixture in the combustion chamber is ignited, thereafter, the combustion reaction proceeds rapidly and ions are generated in the combustion chamber. For this reason, a closed circuit is formed through the ions, and the ionic current i flows through the path of the current detection resistor R2, the current limiting resistor R1, the capacitor C1, the secondary coil L2, and the spark plug PG. Therefore, the output voltage Vo of the ion current detection circuit ION is Vo = R2 * i, which is a value proportional to the ion current i.

  Next, air-fuel ratio control at the time of cold start performed in the above-described combustion control device DET will be described. This air-fuel ratio control suppresses generation of unburned gas at the cold start when the three-way catalyst or the like does not function effectively, and is therefore executed only for a predetermined time after the start of the internal combustion engine.

<First Example>
Based on the above, the first embodiment shown in FIG. 9 will be described. First, the ECU digitally converts the output voltage Vo of the ion current detection circuit ION and stores it in the memory as a detection signal Vo for a specified section in each ignition cycle (ST1). Note that the specified section is normally started from the falling timing (T0) of the ignition pulse SG, but may be started from TDC according to the determination parameter.

Next, an appropriate determination parameter is extracted from the detection signal acquired in the process of step ST1 (ST2). Of the determination parameters P1 to P4 shown below, the case where the determination parameter P3 is used is an example of the present invention, and the other is a reference example.

(P1) Peak position For the detection signal Vo that has finished the LC vibration section, the peak position at which the detection signal Vo indicates the peak value is extracted, and the elapsed time from the falling timing T0 of the ignition pulse SG to the peak position is used as a determination parameter. (See FIG. 2). Note that the elapsed time from the TDC may be used as the determination parameter.

(P2) Post-burn integration value (summation of the subsequent region)
The cumulative value of the subsequent region (for example, 100 to 360 CA) of the detection signal Vo is calculated and used as a determination parameter (see FIG. 3).

(P3) 50% position The elapsed time until the total integrated value of the detection signal Vo reaches a predetermined level (for example, 50%) is used as a determination parameter (see FIG. 4). The base point of the cumulative calculation of all integral values is the falling timing T0 of the TDC or ignition pulse SG, and the end point is, for example, 360 CA where the detection signal disappears reliably.

(P4) Area ratio For each of the preceding region (for example, 0 to 100 CA) and the subsequent region (for example, 100 to 360 CA) of the detection signal Vo, the cumulative calculation is executed to calculate the initial combustion integrated value and the afterburning integrated value. To do. Then, the ratio between the initial combustion integral value and the afterburning integral value is used as a determination parameter (see FIG. 5).

  For any of the determination parameters P1 to P4 described above, the limit values predicted to be insufficient for the output of the internal combustion engine are each experimentally specified as the threshold value TH.

  Therefore, when the process of step ST2 is completed, the extracted determination parameter is compared with the threshold value TH (ST3). If the determination parameter is a normal level, in the next ignition cycle, a preparatory operation necessary to further control the air-fuel ratio to the lean side by a predetermined level is executed (ST4).

  On the other hand, if the determination parameter is a dangerous level, a preparatory operation necessary to improve the combustion state is executed in the next ignition cycle (ST5). For example, measures such as changing the air-fuel ratio to the fuel rich side to mitigate lean combustion, (b) increasing the energization time by extending the energization time of the primary coil, and (c) changing the ignition timing T0 are considered. It is done. As described above, in this embodiment, the optimal air-fuel ratio control can be realized at the cold start without arranging the in-cylinder pressure sensor or the like, and the generation of unburned gas can be suppressed.

  As described above, the embodiment in which the air-fuel ratio control is executed for the next ignition cycle based on the real-time value acquired for each ignition cycle has been described. However, it is also preferable to accumulate a real-time value, calculate a statistical value, and execute air-fuel ratio control based on the statistical value.

<Second Example>
FIG. 10 is a flowchart showing the second embodiment. Here, in order to save the determination parameter DA in each ignition cycle, a buffer area divided into N areas from the start area BUF (TOP) to the final area BUF (BTM) is provided. In addition, a pointer PT is provided to specify the storage destination BUF (TOP) of the time integral value.

Based on the above, the processing content of FIG. 10 will be described. Similarly to the case of FIG. 9, a predetermined determination parameter DA is obtained from the detection signal Vo in the specified section (ST10 to ST11), and is stored in the buffer area BUF (TOP) indicated by the pointer PT (ST12). Also in this case, among the determination parameters P1 to P4 shown below, the case where the determination parameter P3 is used is an example of the present invention, and the other is a reference example.

  In any case, when the storage process in step ST12 is completed, it is next determined whether or not the value of the pointer PT matches the head position TOP. If PT> TOP and does not match, the pointer PT is stored. The value is decremented (−1) and the process is terminated (ST14). In this way, by repeating the processes of steps ST10 to ST14, the determination parameter DA for N ignition cycles is stored in the buffer area from the final area BUF (BTM) to the leading area BUF (TOP). The

  Since the value of the pointer PT matches the value of the head position TOP at the timing when the N determination parameters DA are stored in the N partitioned buffer areas, the moving average value AV of the N determination parameters DA. And standard deviation σ are calculated (ST16). Further, N-1 data of BUF (PT) to BUF (BTM-1) are shifted by one area and moved from BUF (PT + 1) to BUF (BTM) (ST17).

  Next, based on the moving average value AV and the standard deviation σ calculated in step ST16, the variation rate VAR is calculated as VAR = σ / AV, and the calculated variation rate VAR is compared with a predetermined threshold TH (ST18). ). If the fluctuation rate VAR is at a normal level, a preparatory operation necessary to make the air-fuel ratio leaner by a predetermined level Δ is executed in the next ignition cycle (ST19). On the other hand, if the fluctuation rate VAR is at a dangerous level, a preparatory operation necessary for relaxing the air-fuel ratio control is executed in the next ignition cycle (ST15).

  Thus, in the second embodiment, since the statistical value of the determination parameter is evaluated, the determination accuracy can be improved as compared with the case where the determination parameter calculated in real time for each ignition cycle is used. In the determination of step ST18, the variation rate VAR and the threshold value TH are compared. However, the determination is based on the standard deviation σ and moving average value AV of the determination parameter described above, or the standard deviation σ and moving average value AV. It is also preferable to make an abnormality determination based on other statistical values using. In addition, it goes without saying that the above-described evaluation values (including determination parameters) may be used in appropriate combinations.

  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 simplest circuit configuration is illustrated as the ion current detection circuit, but it is needless to say that a more complicated circuit configuration may be adopted.

  In the above-described embodiments, the ECU has been described so as to execute the operations of FIGS. 9 and 10. However, it is also preferable that these processes are performed by a dedicated computer circuit. Preferred examples of the dedicated computer circuit include a DSP (Digital Signal Processor), a one-chip microcomputer, a one-chip microcontroller, and the like.

EQ Combustion control device L1 Primary coil L2 Secondary coil CL Ignition coil Q Switching element ECU Control device Vo Current signal ION Signal detection circuits ST1 to ST3 Determination means ST4 to ST5 Change means

Claims (2)

An ignition coil having a primary coil and a secondary coil, a switching element that controls energization of the primary coil, a control device that performs ON / OFF operation of the switching element, and that performs air-fuel ratio control during cold start, A spark plug that performs ignition discharge in response to an induced voltage of the secondary coil generated in response to a transition operation of the switching element; and a signal detection circuit that detects a current signal that passes through the spark plug. Configured,
Determination means for determining whether or not the combustion operation of the internal combustion engine is appropriate based on the current signal acquired at the time of cold start;
If it is determined by the determination means that the combustion operation is appropriate, the air-fuel ratio control is advanced to the lean side in the subsequent ignition cycle, while if it is determined that the combustion operation is not appropriate, recovery measures to improve combustion in the subsequent ignition cycle are taken. Change means to take,
Is configured to function during cold start,
The determination means is obtained by time-integrating the current signal from the calculation base point set at the ignition timing at which the spark plug ignites and discharges or the TDC (Top Dead Center) of the crank angle until the ionic current disappears reliably. For the total integral value, specify the elapsed time until the time integral value from the calculation base point reaches a predetermined ratio of the total integral value, and whether the combustion operation at the cold start is appropriate based on the elapsed time A combustion control apparatus characterized by determining whether or not . The determination means determines whether or not the combustion operation at the cold start is appropriate by comparing a statistical value relating to the elapsed time calculated from the measured values in a plurality of ignition cycles with a predetermined limit value. The combustion control device according to claim 1.