JP2010053782A - Knock detection device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a knock detection device of an internal combustion engine which allows accurate knock determination even at a preignition. <P>SOLUTION: The device comprises an ECU, an ion current detection circuit ION and a knocking sensor SE. The ECU consists of a first means (ST14) for determining a level of a detection signal Vo from the ion current detection circuit to determine whether or not a combustion state starts when a switching element Q is turned on, and a second means (ST16) for determining that knocking occurs or determining whether or not the knocking occurs by starting an output level determination process of the knocking sensor after the OFF transition operation of the switching element, when it is determined that the combustion state is started by the first means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a knock detection device for an internal combustion engine that realizes accurate knock determination based on ion current.

Knocking (hereinafter abbreviated as “knock”) generally means a phenomenon in which a metallic striking sound is generated due to abnormal combustion of an air-fuel mixture in a combustion chamber of an internal combustion engine. And if this is left unattended, it will lead to further troubles such as the fatigue deterioration of the engine wall surface being promoted, and therefore various methods for reliably detecting knock have been proposed (Patent Document 1).
11-508666

  In the invention described in Patent Document 1, abnormal vibration is detected by a knock sensor disposed in a cylinder of an internal combustion engine, and the presence or absence of knock energy is determined by integrating a knock sensor signal in a predetermined measurement window.

  However, at the time of pre-ignition that occurs when the air-fuel mixture is ignited at an early stage, it is often followed by a knocking state. However, in the fixed measurement window in the prior art, pre-ignition (hereinafter referred to as pre-ignition) The subsequent knock cannot be detected. If the occurrence of knocking is overlooked and this is left unattended, the temperature of the wall in the combustion chamber rises, so that an environment in which plague is more likely to occur is generated, which may seriously damage the internal combustion engine.

Here, although a method for detecting the occurrence of pragging based on the output of the knock sensor is known (Patent Document 2), there is no meaning if the abnormal output of the knock sensor is missed.
JP-A-11-247750

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a knock detection device for an internal combustion engine that enables accurate knock determination even during pre-ignition.

  In order to solve the above problems, a knock detection device for an internal combustion engine according to the present invention includes an ignition coil including a primary coil and a secondary coil, a switching element for controlling energization of the primary coil, and an ignition for the switching element. A control circuit that supplies a signal to perform an ON / OFF operation, an ignition plug that performs a discharge operation by receiving an induced voltage of the secondary coil, and an ion that outputs a detection signal proportional to an ion current indicating a combustion state of the internal combustion engine A control circuit configured to determine a level of the detection signal when the switching element is turned on. A first means for determining whether or not the combustion state is started, and knocking when it is determined by the first means that the combustion state is started. A second means for determining whether or not knocking occurs by starting determination processing of the output level of the knock sensor following the OFF transition operation of the switching element; Are provided.

  The first means of the present invention is: (1) a duration in which the detection signal continuously exceeds a predetermined level, (2) an integrated value of the detection signal that continuously exceeds the predetermined level, and (3) a continuous detection signal. Thus, it is effective to determine the combustion state based on all or part of the excess number exceeding the predetermined level.

  The first means preferably acquires the detection signal for each sampling period, and if the acquired data DT exceeds a predetermined level TH, the first means acquires it in the storage area VOL (i) corresponding to the acquisition number i. While the data is added, if the acquired data DT does not exceed the predetermined level TH, the acquisition number i is increased.

  Alternatively, the first means preferably acquires the detection signal for each sampling period, and when the acquired data DT exceeds a predetermined level TH, the timer variable T is increased while the timer variable T is increased. The value is stored in the storage location TM (i) corresponding to the acquisition number i, and then the acquisition number i is incremented.

  According to the above-described present invention, it is possible to accurately perform knock determination even during pre-ignition and maintain an appropriate operation of the internal combustion engine.

  Hereinafter, the present invention will be described in more detail based on examples. FIG. 1 is a circuit diagram illustrating a knock detection device IGN according to an embodiment.

  As shown in the figure, this knock detection device IGN is based on an ECU (Engine Control Unit) which is an electronic control unit of an internal combustion engine, an ignition coil CL comprising 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 of the primary coil L1 by the transition operation, the spark plug PG that receives the induced voltage of the secondary coil L2, and performs the discharging operation, and the knock detection signal Vo that is proportional to the ion current are output. An ionic current detection circuit ION and a knock sensor SE (not shown) arranged at appropriate positions of the internal combustion engine are mainly configured.

  As shown in the figure, the ECU receives the knock detection signal Vo of the ion current detection circuit ION and the output of the knock sensor SE, but the ECU is configured to store each signal after AD conversion by the built-in AD converter. Has been.

  Here, an IGBT (Insulated Gate Bipolar Transistor) is used as the switching element Q. 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 voltage at the time of detecting an ionic current 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 shown, the cathode terminal of the diode D1 is connected to the ground.

  On the other hand, the cathode 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 a diode D2 is connected between the inverting terminal and the non-inverting terminal.

  2 to 4 are diagrams for explaining the operation contents of the ion current detection circuit ION described above. First, at the ON transition time (timing T0) when the ignition pulse SG changes from the L level to the H level, the switching element Q is turned on, so that the coil current ic1 starts to flow through the primary coil L1. As shown in FIG. 3, at the time of this ON transition, an induced voltage is generated in the secondary coil L so that the high voltage terminal is at a positive level. Flowing.

  Since this transient current also flows through the current detection resistor R2, the output voltage Vo of the OP amplifier AMP becomes a high level only for a short time (see timing T0 in FIG. 2C). At this timing, since the internal combustion engine is in the compression process, the air-fuel mixture introduced into the combustion chamber tends to rise in temperature when pressurized. On the other hand, the voltage across the spark plug PG seems to maintain the high voltage state charged at the timing T0.

  And in the combustion control circuit shown in FIG. 1, in order to make an ion current detection circuit function, the diode which prevents reverse discharge cannot be provided. Therefore, in some cases, the spark plug may discharge in the reverse direction when the switching element is in the ON state and the primary coil is energized.

  As shown in FIG. 2C, it is assumed here that reverse discharge has occurred at the timing of T1. When such reverse discharge occurs, for example, the air-fuel mixture may be ignited at the timing when the temperature of the air-fuel mixture in the compression process further rises, and the combustion reaction may start. When the combustion state is started, an ionic current flows in the direction of the arrow in FIG.

  As described above, FIG. 2 illustrates the case where the pre-ignition occurs due to the reverse discharge. However, even if the reverse discharge does not occur, if the heat source such as carbon sludge exists in the combustion chamber, the compression stroke The air-fuel mixture may be self-ignited by this heat source and become pre-ignited.

  Continuing with FIG. 2, when the ignition pulse SG changes from the H level to the L level at the timing of T3, the switching element Q transitions to the OFF state, and the secondary coil L2 has a high voltage terminal having a negative high voltage. A voltage is induced (see FIG. 4). For this reason, a positive direction discharge current shown in FIG. 4 flows, and the combustion reaction is started when this ignition discharge occurs. However, in the embodiment shown in FIG. 2, the combustion reaction has already started at the timing T2. The reason why the combustion waveform caused by the Plague is interrupted at the timing of T3 is that a plug discharge current at a level much higher than the ion current flows through the path of FIG.

  The capacitor C1 is charged by this plug discharge. Since the Zener diode ZD is connected in parallel to the capacitor C1, the voltage across the capacitor C1 is a constant voltage defined by the breakdown voltage of the Zener diode ZD. Become.

  Thereafter, from timing T3, residual magnetic noise (discharge noise) is generated by the magnetism remaining in the iron core forming the magnetic paths of the primary coil L1 and the secondary coil L2, and after the residual magnetic noise converges, the original combustion reaction Is detected from the ion current detection circuit ION.

  Based on the above operation contents, a preg and knock detection algorithm will be described. FIG. 5A is a flowchart for explaining this detection algorithm. This process is executed in the section of the measurement window WIN shown in FIG. That is, this detection process is started at the timing when the transient current is considered to have converged after the switching element Q is turned ON, and is ended immediately before the switching element Q is turned OFF.

  In the flowchart of FIG. 5A, the variable i is the detection number of the ion detection signal Vo, VOL (i) is an array that stores the accumulated value (integrated value) of the ion detection signal Vo, and TM (i) is significant. An array for storing the duration of the ion detection signal Vo at the level, TH is a threshold value for pre-detection, variable DT is the acquired data obtained by AD conversion of the ion detection signal Vo, and variable T is the duration of the ion detection signal Vo at the significant level The variable FLG is a flag indicating the transition of the H / L level of the ion detection signal Vo.

  Based on the above, FIG. 5A will be described. First, all areas of the array VOL and the array TM are cleared to zero, and the variable i is initialized to 1 (ST1). Next, the flag FLG and the timer variable T are cleared to zero (ST2).

  When the above initial processing is completed, it is determined whether or not the present time is the pre-jugation determination time (ST3). The pre-judge determination time is the end of the measurement window WIN and means the timing immediately before the timing T3 shown in FIG.

  If it is not reached at the time of pre-judge determination, it is determined whether or not the present time is the acquisition timing of the ion detection signal Vo (ST4). For example, when the sampling frequency is set to 30 kHz, whether or not the sampling period (= 1/30 mS) has been reached is determined in the process of step ST4. Note that the arrival of the sampling period is detected by, for example, whether or not a timer interrupt with an interrupt period of 1/30 mS has occurred.

  When the data acquisition timing is reached, the AD converter is activated by software (ST5) and waits for the started AD conversion processing to end (ST6). When the end of AD conversion is confirmed, the ion detection signal Vo subjected to AD conversion is acquired as a variable DT (ST7).

  Next, the acquired data DT is compared with the threshold value TH (ST8). If the acquired data DT is smaller than the threshold value TH (DT <TH), the process proceeds to step ST10 and the value of the flag FLG is determined. (ST10). Since the threshold value TH is set to a sufficiently high level, if the ion detection signal Vo is a simple noise level, DT <TH and the value of the flag FLG is determined.

  The flag FLG is set to zero in the initial stage (ST2), but after the ion detection signal Vo exceeds the threshold, the flag FLG is 1 (ST9). Therefore, if FLG = 0, it means that the ion detection signal Vo is continuously at a low level. Therefore, the process proceeds to step ST3 and waits until the next data acquisition timing is reached.

  On the other hand, if FLG = 1 at the timing of step ST10, it means that the ion detection signal Vo that has once increased to a high level has subsequently decreased to a low level. Therefore, in this case, the duration measured by the timer variable T in a state where the ion detection signal Vo is maintained at a high level is stored as the i-th element of the array TM (ST11). With this process, since the process for the i-th significant data regarding the ion detection signal Vo is completed, the variable i is incremented and the process proceeds to step ST2 (ST11). As a result, the timer variable T is initialized to zero, and the flag FLG is also initialized to zero (ST2).

  By the way, when it is determined in step ST8 that the acquired value DT of the ion detection signal Vo is equal to or greater than the threshold value TH, the acquired value DT is added to the i-th element of the array VOL (ST9). . By this processing, the total value (integrated value) of the ion detection signal Vo that continuously shows a significant level is stored in the array VOL (i).

  In step ST9, the flag FLG is set to 1, and the timer variable T is incremented, and the process returns to step ST3. The increment process of the timer variable T in step ST9 is nothing but the process of measuring the time during which the ion detection signal Vo continues to show a significant level, and the measured duration is stored in the timer variable T. This duration is stored in the array TM (i) by the process of step ST11 at the moment when the ion detection signal Vo falls.

  If the above processing is repeated, it will eventually reach the pre-judge determination time (ST3). At this preg determination timing, first, the value of the flag FLG is determined (ST12). If FLG = 1, the duration time measured by the process of step ST9 is stored in the array TM (i). (ST13).

  The value of the variable i at this timing indicates how many ion detection signals Vo having a significant level exceeding the threshold value TH are detected in the section of the measurement window WIN. In the normal operation state, the detected number i is 0, but i ≠ 0 at the time of abnormality in which reverse discharge shown in FIG.

  For example, if the detected number i = 1, it can be estimated that reverse discharge (on-time discharge) has occurred but has not reached the pre-ignition. Alternatively, when the detected number i = 1, reverse discharge (on-time discharge) does not occur, and there is a possibility of reaching the pre-ignition.

  However, which situation has occurred can be estimated from the duration TM (1) when the ion detection signal Vo has a significant level or the integral value VOL (1).

  Further, if the detected number i = 2, it can be estimated that reverse discharge (on-time discharge) has occurred and then has reached the pre-ignition.

  Therefore, the value n of the variable i, the values of the arrays TM (1) to TM (n), and the values of the arrays VOL (1) to VOL (n) are comprehensively evaluated. It is determined whether or not it has occurred (ST14). If it is determined that the occurrence of pre-ignition has occurred, there is a high possibility that a knock will occur thereafter, so that the determination window for the knock sensor is corrected to the front side of the time axis so that the knock is not overlooked ( ST16). The start period of this acquisition window is set, for example, at a timing T3 shown in FIG.

  As a result, the knock sensor does not miss the knock signal generated prior to the residual magnetic noise. It should be noted that knocking occurs with a very high probability following the occurrence of preg. Therefore, it is also preferable to execute the subsequent combustion control by assuming that knocking has occurred when authorizing the occurrence of preg.

  On the other hand, when it is concluded by the determination in step ST14 that no paging has occurred, the knock sensor signal is acquired in a normal determination window. In this case, the start of the determination window is the peak position of the ion detection signal after the residual magnetic noise generated after the switching element Q is turned off. Further, the end is the position where the ion detection signal converges. Both the start time and the end time are experimentally determined corresponding to the operating state of the internal combustion engine, and a value corresponding to the operating state at that time is selected.

  FIG. 5B illustrates an ion detection signal and an output waveform of the knock sensor. As shown in the figure, the output amplitude of the knock sensor is remarkably increased after the play, and it is confirmed that knocking has occurred. In the normal case, since the output of the knock sensor is not acquired until after the residual magnetic noise has converged, the occurrence of knocking may be overlooked. There is no oversight.

  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, the prag detection method shown in FIG. 5 is merely an example, and it goes without saying that other methods may be adopted. Further, the circuit configuration of the ion current detection circuit may be changed as appropriate.

It is a circuit diagram which shows the structure of the knock detection apparatus based on an Example. It is a time chart explaining operation | movement of the knock detection apparatus of FIG. It is a figure explaining the abnormal operation at the time of ON transition of a switching element, and after that. It is drawing explaining the operation | movement at the time of OFF transition of a switching element. It is a flowchart explaining the operation | movement content of the knock detection apparatus shown in FIG.

Explanation of symbols

L1 Primary coil L2 Secondary coil CL Ignition coil ECU Controller SG Ignition signal Q Switching element PG Ignition plug ION Ion current detection circuit SE Knock sensor ST14 First means ST16 Second means

Claims (4)

An ignition coil composed of a primary coil and a secondary coil, a switching element for controlling energization of the primary coil, a control circuit for supplying an ignition signal to the switching element to perform an ON / OFF operation, and induction of the secondary coil An ignition plug that receives a voltage to perform a discharging operation, an ion current detection circuit that outputs a detection signal proportional to an ion current indicating a combustion state of the internal combustion engine, a knock sensor that is disposed at a proper position of the internal combustion engine and detects vibration Configured with
The control circuit includes:
A first means for determining a level of the detection signal during an ON operation of the switching element to determine whether or not a combustion state is started;
When it is determined that the combustion state is started by the first means, it is determined that knocking has occurred, or the output level of the knock sensor is determined following the OFF transition operation of the switching element. A second means for starting the determination process and determining whether knocking occurs;
A knock detection device for an internal combustion engine, comprising: The first means includes
Duration for which the detection signal continuously exceeds a predetermined level,
An integral value of the detection signal continuously exceeding a predetermined level,
The number of times that the detection signal continuously exceeds a predetermined level,
The knock detection device according to claim 1, wherein the combustion state is determined based on all or a part of. The first means includes
The detection signal is acquired every sampling period,
When the acquired data DT exceeds the predetermined level TH, the acquired data is added to the storage area VOL (i) corresponding to the acquisition number i. On the other hand, when the acquired data DT does not exceed the predetermined level TH, the acquisition number The knock detection device according to claim 1 or 2, wherein i is increased. The first means includes
The detection signal is acquired every sampling period,
When the acquired data DT exceeds the predetermined level TH, the timer variable T is increased, while the value of the timer variable T is stored in the storage location TM (i) corresponding to the acquisition number i, and then acquired. The knock detection device according to claim 1, wherein the number i is increased.

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