JP2014122577A - Combustion control device of internal combustion engine - Google Patents

Abstract

Disclosed is a combustion control device capable of detecting plug deterioration at an early stage and preventing misfire.
Processing for determining a discharge time of a spark plug based on a detection signal acquired from a detection circuit, and determining whether the determined discharge time is below a limit value defined for each operating condition (ST1). ST2), processing for determining whether or not the spark plug has deteriorated beyond the use limit based on the total value of the determination results (ST3 to ST4), and when it is determined that the spark plug has deteriorated Then, the process (ST5) which aims at avoiding misfire by performing the combustion control which suppressed target value is provided.
[Selection] Figure 3

Description

  The present invention relates to a combustion control device for an internal combustion engine such as an automobile engine, and more particularly to a combustion control device that detects deterioration of a spark plug at an early stage and operates to prevent misfire.

  In the internal combustion engine, with the air-fuel mixture introduced into the combustion chamber, the ignition plug is ignited and discharged to start combustion of the air-fuel mixture. Thus, since the ignition plug repeats ignition discharge every ignition cycle, its deterioration is unavoidable and naturally has a use limit.

  However, since the driving mode and the driving environment are different for each user, the use limit of the spark plug cannot be simply defined based on the number of times of ignition or the like, and the deteriorated spark plug may continue to be used. .

  When the spark plug deteriorates, the dielectric breakdown voltage increases and the discharge time for sustaining the spark discharge is shortened by the wide plug gap of the spark plug. Therefore, for example, in a high EGR (Exhaust Gas Recirculation) region, a misfire condition tends to occur due to a high in-cylinder flow velocity. Further, in a high load region where the accelerator pedal is depressed, the cylinder pressure is high, so that the breakdown voltage is further increased and the discharge time is shortened. For this reason, for example, when an event occurs on a slope, it is very dangerous, and there is a possibility of developing a serious accident.

JP 2012-219688 PR JP 2012-197785 PR JP 2012-126189 A JP2012-092809 Japanese Laid-Open Patent Publication No. 2012-082712 JP2012-0777719

  Here, the occurrence of the misfire state itself can be detected based on the rotational fluctuation of the internal combustion engine, the behavior of the ions generated in the combustion chamber, the pressure detection of the intake pipe, etc. In view of the possibility of accidents as described above in Patent Document 6), combustion control that can prevent the occurrence of misfire is desired.

  The present invention has been made in view of the above-described problems, and detects plug deterioration at an early stage. If plug deterioration is recognized, special combustion control is realized to prevent misfire. An object of the present invention is to provide a combustion control device that can prevent the above.

  To achieve the above object, the present invention provides an ignition coil having a primary coil and a secondary coil, a switching element that controls energization of the primary coil, and an ON / OFF signal by supplying an ignition signal to the switching element. A control device that operates, a spark plug that performs a discharge operation in response to an induced voltage of the secondary coil, and a detection circuit that outputs a detection signal capable of specifying the discharge operation of the spark plug, After the ignition signal is supplied to the switching element, the discharge time of the spark plug is grasped based on the detection signal acquired from the detection circuit, and the grasped discharge time is less than a limit value defined for each operating condition. A first means for determining whether or not, a second means for determining whether or not the spark plug has deteriorated beyond the use limit based on the total value of the determination result of the first means, and a second means When the spark plug is determined has deteriorated I it is then is characterized in that it comprises a third means for achieving the avoidance of misfire by executing the combustion control that suppresses a target value.

  According to the study of the present inventor, as schematically shown in FIG. 1, the discharge time (duration duration) of the spark plug decreases as the operating load increases. The reason is that the higher the operating load, the higher the pressure inside the tube, and the higher the breakdown voltage. And when plug deterioration, it became clear that even if it is the same driving load and the charging energy charged to an ignition coil is the same, discharge time decreases. Further, as schematically shown in FIG. 1 (b), when the discharge time decreases corresponding to the flow velocity in the cylinder, it is clear that the discharge time decreases even when the plug is deteriorated even with the same operating load. It became.

  Therefore, according to the characteristic shown in FIG. 1 described above, when the plug is deteriorated, even if ignition discharge is realized, the duration is short and the possibility that the fire type disappears and misfires is high. However, in the present invention, plug deterioration is detected quickly, and control is performed without increasing the operating load (see the one-dot chain line in FIG. 1 (a)) and without increasing the in-cylinder flow velocity when the plug deteriorates. (See the alternate long and short dash line in FIG. 1B), the occurrence of misfire is prevented. In the present invention, when the plug is deteriorated, since the suppression control below the target value is executed, a dangerous state can be avoided while the original operation output cannot be obtained, but the driver is informed of the plug deterioration, By requesting replacement of the spark plug, an appropriate operating state can be recovered.

  In the present invention, the limit time of the discharge time of the spark plug is defined for each operating condition, and the operating condition is specified by, for example, the rotational speed of the internal combustion engine and the operating load. The operating load is specified by, for example, the intake pipe pressure when the third means is not functioning.

  The third means of the present invention is realized, for example, in an electronically controlled throttle system by suppressing the amount of intake air into the combustion chamber regardless of the amount of operation with respect to the accelerator pedal. Here, the electronically controlled throttle system means a mechanism that electrically connects and controls the accelerator pedal and the engine throttle, and in this embodiment, the intake air amount is lower than the original target value, so the cylinder pressure The ignition discharge is stabilized even in the deteriorated plug as much as the increase in the amount is suppressed, and the misfire state can be avoided in advance.

  The third means of the present invention is preferably realized by suppressing the amount of EGR in EGR control. Here, the EGR control means a control for taking out a part of the exhaust gas after combustion, guiding it to the intake side, and taking it in again, thereby reducing nitrogen oxides in the exhaust gas and improving fuel consumption. . If the EGR amount increases in this EGR control, the ignition spark may be blown off. In particular, since the discharge time is short when the plug is deteriorated, this possibility increases. In this embodiment, the EGR amount is suppressed. Therefore, the possibility of misfire can be reduced. Note that the present invention is applicable to both the external EGR and the internal EGR.

  The third means of the present invention is preferably realized by suppressing the control amount of the supercharging pressure control. Here, the supercharging pressure means compressed air pressure that is forcibly sent to the internal combustion engine by the supercharger. For example, in a reciprocating engine, a supercharger supplied from a supercharger such as a turbocharger or a supercharger. In general, the output increases as the supply pressure increases. However, in this embodiment, when the plug is deteriorated, the supply of the supercharging pressure is stopped or suppressed, so that the possibility of misfire due to the supercharging pressure is reliably reduced.

  In the present invention, after the ignition signal is supplied to the switching element, the discharge time of the spark plug is grasped based on the detection signal acquired from the detection circuit, and the grasped discharge time is defined for each operating condition. A fourth means for determining whether or not the reference value is exceeded, a fifth means for determining whether or not the spark plug has been replaced based on a total value of determination results of the fourth means, and a spark plug by the fifth means. After that, it is preferable to execute the determination process based on the updated limit value or reference value as necessary.

  The detection circuit of the present invention includes, for example, a configuration for detecting a voltage of a primary coil after ignition discharge is started, a configuration for detecting a current of a secondary coil after ignition discharge is started, and a combustion state of an internal combustion engine. It is effective to adopt a configuration that outputs a detection signal proportional to the ion current shown.

  According to the present invention described above, it is possible to realize the combustion control capable of preventing the occurrence of misfire by detecting the plug deterioration at an early stage and realizing the special combustion control if the plug deterioration is recognized. .

It is drawing explaining the principle of operation of this invention. It is a circuit diagram which shows the structure of the combustion control apparatus which concerns on 1st Example and 2nd Example. It is a flowchart explaining the operation | movement content of a combustion control apparatus. It is a circuit diagram which shows the structure of the combustion control apparatus of 3rd Example. It is a circuit diagram which shows the structure of the combustion control apparatus of 4th Example. It is a time chart which shows operation | movement of the detection circuit of 3rd Example. It is a time chart which shows operation | movement of the detection circuit of 4th Example.

  Hereinafter, examples will be described in more detail. FIGS. 2A and 2B are circuit diagrams showing the combustion control device CTL according to the first embodiment and the second embodiment.

  The combustion control device CTL shown in FIG. 2 is a transition operation based on 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 PLS received from the ECU. A switching element Q for controlling ON / OFF of the current of the primary coil L1, a spark plug PG that receives a voltage induced by the secondary coil L2, and performs a discharge operation; a detection circuit DET that can detect a discharge time of the spark plug PG; , It is structured around.

  Here, the ECU can determine whether the spark plug should be evaluated as being deteriorated or evaluated as having been replaced with a spark plug having a different characteristic in accordance with the operation conditions at that time. Is provided. The operating conditions are specified by, for example, the engine intake pipe pressure, the engine speed, and the like, and by searching the reference table TBL using these as search keys, the average discharge time at that time for each operating condition. (Reference value) and the minimum value (limit value) allowable as normal discharge time are specified. The reference table TBL is arranged in a rewritable nonvolatile memory, and when it is determined that the spark plug has been replaced, a reference value and a limit value are newly stored corresponding to the new spark plug. Is done.

  Although not particularly limited, for example, an IGBT (Insulated Gate Bipolar Transistor) is used as the switching element Q. In this case, the gate terminal of the switching element Q receives the ignition pulse PLS, and the collector terminal receives the battery voltage VB via the primary coil L1. The emitter terminal is connected to the ground.

  As illustrated, the detection circuit DET in FIG. 2A is configured to acquire a detection voltage from the collector terminal (detection point X) of the switching element Q. The potential at the detection point X is at the ground level when the switching element Q is turned on, but after the ignition pulse PLS is interrupted and the switching element Q is turned off, the detection point X has a discharge current flowing through the secondary coil L2. The primary back pressure corresponding to

  Thereafter, the potential at the detection point X converges to a steady level (VB) corresponding to the convergence of the discharge current. Therefore, the ECU specifies the discharge time of the spark plug PG based on the elapsed time from when the primary back pressure is generated and converged.

  On the other hand, the detection circuit DET in FIG. 2B is configured to acquire the voltage across the detection resistor Rs connected in series to the secondary coil L2 as the detection voltage. Since the potential at the detection point X is detected at a predetermined level during ignition discharge, the ECU specifies the ignition discharge time of the ignition plug PG based on the value.

  FIG. 3A is a flowchart for explaining the operation of the ECU, and shows the operation executed at the time of ignition discharge of the ignition coil. The ECU specifies the discharge time (discharge duration) based on the detection signal from the detection circuit DET (ST1). Next, with reference to the reference table TBL corresponding to the operation condition at that time, the reference value and the limit value are specified, and compared with the discharge time specified in the process of step ST1, and until that time, step ST3 Also, it is compared with the past data accumulated in the process of ST6 (ST2).

  If the discharge time is an abnormally low level that is less than the limit value, this is stored, and the discharge time of the abnormally low level accumulated so far is totaled to calculate a statistical value (ST3). The statistical value is not particularly limited, and the occurrence frequency of abnormally low level discharge time, the average value of abnormally low level discharge time, and the like correspond to this.

  Then, when the occurrence frequency of the discharge time below the limit value is high, or when the average value is abnormally low (ST4), it is evaluated that the plug is deteriorated and this is notified to the driver. In addition to notifying, in order to avoid misfire in the subsequent ignition cycle, the combustion control is changed to suppressed combustion control (ST5).

  As a result, in the subsequent ignition cycle, combustion control with the target value suppressed is executed. Specifically, (a) in the electronically controlled throttle system, suppressing the intake air amount to the combustion chamber irrespective of the operation amount with respect to the accelerator pedal, (b) suppressing the EGR amount in the EGR control, (c) excessive All or part of the control amount of the supply pressure control is appropriately selected and executed.

  On the other hand, in the comparison / determination of step ST2, if it is evaluated that the discharge time specified in the process of step ST1 greatly exceeds the reference value or is greatly improved from the past data, this is stored. The statistical values are calculated by collecting the abnormally high level discharge time accumulated so far (ST6). The statistical values in this case also correspond to, for example, the occurrence frequency of abnormally high level (improvement level) discharge times, the average value of abnormally high level discharge times, and the like.

  And when the occurrence frequency of the improvement level discharge time is high, or when the average value is abnormally high level (ST7), it is evaluated that the spark plug has been replaced. In order to change the reference value and the limit value, the data in the reference table TBL is rewritten (ST8). Further, when the combustion control suppressed until that time has been executed, normal combustion control is executed thereafter (ST8).

  As described above, according to the present embodiment, the deterioration of the plug can be detected at an early stage and the occurrence of misfire can be prevented, so that the occurrence of an accident due to an engine trouble can be prevented.

  By the way, the method for specifying the discharge time of the spark plug is not limited to the circuit configuration of FIG. FIG. 4 is a circuit diagram showing the detection circuit DET of the third embodiment, and shows current paths at the time of ignition discharge (a) and after the end of ignition discharge (b). The circuit configuration other than the detection circuit DET is the same as in the first and second embodiments.

  The illustrated detection circuit DET is configured to detect an ion signal Vo generated in the combustion chamber, and operates as an inverting amplifier, an OP amplifier AMP, a capacitor C1, a Zener diode ZD, diodes D1 and D2, and resistors R1 to R1. And R3. Here, a bias voltage at the time of ion signal detection is generated by a parallel circuit of the capacitor C1 and the Zener diode ZD.

  In the illustrated detection circuit DET, 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. 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 device CTL configured as described above, the ignition plug PG is discharged by the high voltage induced in the secondary coil L2 at the falling timing of the ignition pulse PLS (see FIG. 6A). Since this discharge current flows through the path of the ignition plug PG → secondary coil L2 → capacitor C1 → diode D1 (minus discharge path), the capacitor C1 is charged to a voltage value defined by the breakdown voltage of the Zener diode ZD. (See FIG. 4 (a)).

  When the air-fuel mixture in the combustion chamber is ignited by the discharge of the ignition plug PG, the combustion reaction proceeds rapidly thereafter, but the ionic current i is the current detection resistance R2 → current limiting resistance R1 → capacitor C1 → secondary coil L2. → Flows through the spark plug PG. Therefore, the output voltage Vo of the OP amplifier AMP is Vo = R2 * i, which is an ion signal proportional to the ion current i.

  FIG. 6 is a time chart showing the contents of this operation, and the timing at which the ion signal increases significantly means that the ignition discharge has ended. Therefore, in this embodiment, the discharge time is specified by the period from the time when the ignition pulse PLS falls to the timing when the ion signal exceeds the threshold TH of a predetermined level.

  Specifically, as shown in FIG. 3B, the discharge time specifying process (ST1) in the third embodiment is shown. After the ignition pulse is lowered, the ECU clears the variable i (ST11), and updates the variable i every sampling cycle (ST16), and executes the processes of steps ST12 to ST20.

  Specifically, first, the detection signal SG (i) as the ion signal Vo is acquired, and the detection signal SG (i) is converted into a pulse signal based on whether or not the threshold value TH is exceeded (ST12). If the pulse signal is at the L level, the determination flag FLG is set to 0, the variable i is incremented, and the process returns to step ST12.

  On the other hand, if an H-level pulse signal is obtained, it is next determined whether or not the determination flag FLG is 0 at that timing (ST17). Here, if FLG = 0, it means that the pulse signal has increased to the H level for the first time at this timing. In this case, therefore, the determination flag FLG is set to 1 and the value of the variable i is substituted into the variable ST that defines the start timing (ST18).

  Therefore, when the pulse signal obtained by pulsing the detection signal SG (i) sampled thereafter is at the H level, the process of step ST18 is skipped. If the sampling of the detection signal is repeated while repeating such processing, the difference between the variable i and the variable ST will eventually increase, so that the H level is continued beyond the reference width Δ. The discharge time is defined as i−Δ (ST20). The reason why the reference width Δ is provided is to prevent erroneous determination by eliminating the influence of noise.

  The detection circuit DET in FIG. 4 that realizes negative discharge has been described above. However, the detection circuit DET in FIG. 5 that realizes positive discharge can also be used. In this detection circuit, the discharge current due to the high voltage induced in the secondary coil L2 flows through the path of diode D1 → capacitor C1 → diode D2 → secondary coil L2 → ignition plug PG (plus discharge path). The battery is charged to a voltage value defined by the breakdown voltage of the Zener diode ZD (see FIG. 5A). At this time, since a current passing through the resistor R3 → the resistor R2 also flows, the output of the OP amplifier AMP becomes a positive saturation level (see FIG. 7).

  Thereafter, when the ignition discharge stops, an ion current i flows through a path of the resistor R3 → the resistor R2 → the capacitor C1 → the resistor R1 → the secondary coil L2 → the spark plug PG. However, there is a section where the current becomes zero for a short time before the ion current starts to flow (see FIG. 7). Therefore, in the detection circuit DET of the fourth embodiment, the detection signal SG (i) that is the ion signal Vo is acquired and converted into a pulse signal based on whether or not the threshold value TH is exceeded. The period until the first change to the L level can be specified as the ignition time.

  Then, the specified ignition time is evaluated through the processing of steps ST2 to ST8 in FIG. 3, and it is determined whether or not the spark plug is in a deteriorated state or whether or not the spark plug has been replaced. Moreover, since the combustion control corresponding to this evaluation result is executed, it is possible to prevent the occurrence of misfire.

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

L1 Primary coil L2 Secondary coil CL Ignition coil Q Switching element ECU Controller PG Spark plug DET Detection circuits ST1 to ST2 First means ST3 to ST4 Second means ST5 Third means

Claims (6)

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 supplies an ignition signal to the switching element to perform an ON / OFF operation, and induction of the secondary coil A spark plug that performs a discharge operation in response to a voltage, and a detection circuit that outputs a detection signal capable of specifying the discharge operation of the spark plug;
After the ignition signal is supplied to the switching element, the discharge time of the spark plug is grasped based on the detection signal acquired from the detection circuit, and the grasped discharge time is less than a limit value defined for each operating condition. A first means for determining whether or not;
Second means for determining whether or not the spark plug has deteriorated beyond the use limit based on the total value of the determination result of the first means;
If it is determined by the second means that the spark plug has deteriorated, thereafter, third means for avoiding misfire by executing combustion control with the target value being suppressed,
A combustion control device for an internal combustion engine, comprising:   The third means includes all or one of suppressing the intake air amount to the combustion chamber regardless of the artificial operation amount, suppressing the EGR amount in the EGR control, and suppressing the control amount of the supercharging pressure control. The combustion control device according to claim 1, which is realized by a unit. After the ignition signal is supplied to the switching element, the discharge time of the ignition plug is grasped based on the detection signal acquired from the detection circuit, and whether the grasped discharge time exceeds the reference value defined for each operating condition. A fourth means for determining whether or not;
Fifth means for determining whether or not the spark plug has been replaced based on the total value of the determination result of the fourth means;
3. The combustion control according to claim 1, wherein when it is determined that the spark plug has been replaced by the fifth means, thereafter, the determination process is executed based on the updated limit value or reference value as necessary. apparatus.   The combustion control device according to claim 1, wherein the detection circuit has a configuration for detecting a voltage of a primary coil after ignition discharge is started.   The combustion control device according to any one of claims 1 to 3, wherein the detection circuit has a configuration for detecting a current of a secondary coil after ignition discharge is started.   The combustion control device according to any one of claims 1 to 3, wherein the detection circuit is configured to output a detection signal proportional to an ion current indicating a combustion state of the internal combustion engine.

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