JP2010059937A - Combustion control device for internal combustion engine - Google Patents

Abstract

Disclosed is a combustion control device capable of accurately extracting a peak position of an ion current regardless of an operating state of an internal combustion engine.
A control unit ECU for turning on / off a switching element Q for controlling energization of a primary coil L1, an ion current detection circuit ION for outputting a detection signal Vo proportional to an ion current indicating a combustion state of an internal combustion engine, , And is configured. The control device ECU analyzes an acquisition process (ST1) for acquiring the detection signal Vo when the switching element Q is in the OFF state, analyzes the waveform of the acquired detection signal Vo, and determines a valley having a depth greater than or equal to a predetermined time. A search process (ST4) for searching from the rear of the axis toward the front, a specific process (ST5) for searching the time axis backward from the first detected valley and identifying the peak position of the waveform of the detection signal; Processing for performing abnormality determination and / or combustion control based on the identified peak position (ST6, ST7).
[Selection] Figure 3

Description

  The present invention relates to an apparatus capable of appropriately controlling combustion in an internal combustion engine such as an automobile engine, and more particularly to a combustion control apparatus capable of accurately extracting a peak position of an ion current regardless of the operating state of the internal combustion engine.

The applicant has previously proposed a combustion control device that can accurately extract the peak position and peak value of the ion current regardless of the fluctuation of the operating state of the internal combustion engine (Patent Document 1).
JP 2007-270831 A

  In this invention, based on the data determination process for differentially calculating whether or not the calculation result exceeds a predetermined value, and the determination result in the data determination unit, the differential calculation of the ionic current signal at the time of primary coil cutoff, A first region where the differential calculation result generally indicates the first level and a second region where the second level generally indicates the second level are extracted, and the boundary between the first region and the second region is the second peak of the ion current. The location is specified.

  In general, when the internal combustion engine is burning normally, the ionic current shows a first peak, then decreases before the top dead center TDC, increases again, and near the crank angle at which the combustion pressure becomes maximum. It is known that the second peak of ion current is exhibited. Then, the occurrence of knocking can be detected by analyzing the waveform in the latter half from the position of the second peak.

  Also, appropriate MBT (Minimum Advance for the Best Torque) control can be performed based on the position of the second peak. Here, the MBT control means that the ignition timing is controlled so that the maximum torque can be obtained when the engine speed and the air-fuel ratio are constant. In general, when the ignition timing conforms to the MBT, The pressure peak position at which the maximum value of the combustion pressure coincides with a point delayed by a predetermined value (for example, 15 ° crank angle) from the top dead center TDC. On the other hand, the peak position of the combustion pressure and the second peak position of the ionic current substantially coincide.

  Therefore, if the second peak position of the ionic current can be accurately grasped, it is determined how much the second peak position is retarded or advanced from the top dead center TDC, and the ignition timing at that time is relative to the MBT. It is possible to determine how much the deviation has occurred.

  As described above, it is extremely important to accurately detect the second peak of the ion current. For example, in the operation region where the engine load is low, the second peak of the ion current is small. There was a problem that the first peak was erroneously determined as the second peak. FIG. 5 exemplifies an ion current waveform indicating a second peak that is difficult to detect. When the second peak is misidentified as a steep first peak rather than the original second peak. Is shown.

  In such a case, knocking is determined or MBT control is performed based on the misidentified second peak, and smooth combustion control cannot be realized.

  The present invention has been made paying attention to this problem, and an object of the present invention is to provide a combustion control device that can accurately extract the peak position of the ion current regardless of the operating state of the internal combustion engine.

  In order to achieve the above object, a combustion control apparatus according to the present invention provides an ignition coil composed of a primary coil and a secondary coil, a switching element for controlling energization of the primary coil, and an ignition signal to the switching element. Control device for ON / OFF operation, spark plug that performs discharge operation upon receiving the induced voltage of the secondary coil, and ion current detection circuit that outputs a detection signal proportional to the ion current indicating the combustion state of the internal combustion engine And the control device analyzes the waveform of the detection signal acquired by the acquisition means for acquiring the detection signal when the switching element is in the OFF state, and has a depth greater than or equal to a predetermined depth. A search means for searching for a valley having a length from the rear to the front of the time axis, and searching for the rear of the time axis from the valley first detected by the search means Specifying means for specifying a peak position of No. waveform based on the identified peak position, the abnormality determination, and / or configured to have a control means for performing combustion control, the.

  Typically, whether or not knocking has occurred is determined to be abnormal, and MTB control is employed as combustion control. In any case, in the present invention, the search means searches for a trough having a depth greater than or equal to a predetermined depth from the rear to the front of the time axis, so that the target peak position is determined regardless of the waveform of the detection signal. Accurate judgment and control are possible without overlooked.

However, when a noise component is superimposed on the detection signal, it is preferable to operate the search means after removing the noise component. The noise component to be removed is typically spike noise.
In the present invention, it is preferable to determine whether or not the valley has a predetermined depth or more based on a deviation between a level of the detection signal at the specific position and an average value of the levels of the detection signals before and after the specific position. The front and rear positions are determined based on the sampling period of the acquisition means, and the time width is preferably set to about 100 to 150 μS before and after.

  The deviation is preferably normalized and compared with a threshold value. It is preferable to provide an accumulating means for calculating a temporal accumulation value of the detection signal after the convergence of the vibration noise generated after the spark plug is discharged. In this case, the deviation is normalized by the accumulation value.

  According to the present invention described above, the peak position of the ion current can be accurately extracted regardless of the operating state of the internal combustion engine.

  Hereinafter, the present invention will be described in more detail based on examples. FIG. 1 is a circuit diagram showing a combustion control device IGN according to an embodiment, and FIG. 2 is a time chart showing schematic waveforms of respective parts of the combustion control device IGN.

  As shown in FIG. 1, this combustion control device IGN 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 ion current detection circuit ION is supplied to an A / D converter (not shown) of the ECU and stored as digital data in a memory of the ECU. Here, the output voltage Vo of the ionic current detection circuit ION is acquired in the data acquisition section that starts from the fall of the ignition pulse SG, and after all the data is acquired, the optimum data is obtained by software processing described later. An analysis interval is determined (see FIG. 2).

  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 shown, 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 IGN configured as described above, 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 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 along the path of 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.

  Then, the abnormality determination and combustion control method of a present Example are demonstrated. FIG. 3 is a flowchart for explaining the operation content of the ECU.

  The ECU lowers the ignition pulse SG (T0), cuts off the current of the primary coil L1, and then digitally converts the output voltage Vo of the ion current detection circuit ION for a predetermined data acquisition section. Is stored in the memory (ST1). The sampling frequency is not particularly limited, but is set to about 30 KHz in this embodiment. Note that the data acquisition section ends at the timing when the combustion reaction is surely completed, but this end END is experimentally determined in advance corresponding to the operating state.

  When the data acquisition process of the data acquisition section is completed, the acquired data is analyzed and the start time of the cut window WIN is determined (ST2). Specifically, the time when the residual magnetic noise due to the residual magnetism of the magnetic path of the ignition coil CL is detected is detected by software processing, and the timing is cut out and set to the start of the window WIN. The end of the extraction window WIN is the same as the end END of the data acquisition section. In addition, for example, the technique of Japanese Patent Application No. 2007-290609 is used to detect the convergence time of the residual magnetic noise.

  Next, if the noise component is included in all the data of the cut window WIN, it is removed by software processing (ST3). The noise component is typically corona noise, which appears in a spike shape, and can be detected based on its specifically narrow pulse width.

  When the noise component is removed, the data analysis sections DET to END are specified from the waveform characteristics of the data after the noise removal (ST4). Data analysis sections DET to END are sections for detecting the second peak position PEAK of the ion current waveform, and are sections for knocking determination.

  Next, the second peak position PEAK is specified by analyzing the data in the specified data analysis sections DET to END (ST5). Then, knocking determination is performed based on data after the second peak position PEAK (ST6). Further, based on the specified second peak position PEAK, MBT control is executed to optimize the next ignition timing (ST7).

  FIG. 4A is a flowchart for specifically explaining the processing contents from the identification processing (ST4) of the data analysis sections DET to END to the knocking processing (ST6).

  In the data analysis section specifying process (ST4), N pieces of data after noise removal included in the cutout window WIN are analyzed. For convenience of explanation, it is assumed that N pieces of data are stored in the arrays S (1) to S (N), i is a variable indicating the array number, and d is a data interval. ing.

  The data interval d is a parameter for determining the start DET of the data analysis interval, and is determined based on the frequency of the ion current and the sampling frequency. Here, since the sampling frequency is 33 kHz, the data separation distance d is set to d = 4. Therefore, in this embodiment, the data separation distance d is about ± 120 μS in terms of time.

  Based on the above, the flowchart of FIG. First, in order to execute the integration process of the ion current signal Vo, an accumulation operation is executed for N pieces of data S (i) in the window WIND (ST40). Specifically, for i = 1 to N, the sum ΣS (i) of the data S (i) is obtained, and this is set as the accumulated value INTG.

  Next, the waveform is checked in the reverse direction from the final data S (N) of the cut window WIND toward the first data S (1), and the valley of the waveform is detected (ST41 to ST46). Specifically, while reducing the variable i from i = N−d to i = d, for each data S (i), the data S (i + d) behind the time axis and the data S ( An average value of i−d) is obtained and set to an intermediate value {S (i + d) + S (id)} / 2 = MD (i) (ST42).

  Next, a deviation Δ (i) = MD (i) −S (i) between the calculated intermediate value MD (i) and the data S (i) is obtained, and this deviation Δ (i) is obtained from the ion current signal. Normalization is performed with the accumulated value INTG (ST43). For the normalization process, an operation of ΔS (i) = Δ (i) / INTG is used.

  Next, the normalized deviation ΔS (i) is compared with a predetermined threshold TH (ST44). If the normalized deviation ΔS (i) ≦ the threshold TH, the variable i is decreased. (ST45), the same processing is repeated.

  If such processing is repeated, data S (i) satisfying normalized deviation ΔS (i)> threshold value TH is eventually detected (ST44), and the data position i is stored in the variable DET. The process ends (ST47). Through the above processing, it is specified that the data analysis section is DET to END. In this embodiment, the point at which the slope of the ion current signal Vo suddenly changes from a large state in the negative direction to a small state in the positive direction in the time axis direction is detected from the rear to the front of the data, and is detected. The point is set as the start point DET of the data analysis section. The detected start point DET of the data start interval is none other than the end timing of the first peak of the ion current.

  Next, a slightly rear position is searched from the start point DET of the data analysis section, and the peak position PEAK is specified (ST5). FIG. 4B schematically shows the start point DET of the detected data analysis section and the identified peak position PEAK. Since the data analysis sections DET to END and the second peak position PEAK of the ionic current are determined by the above processing, the knocking processing is executed next.

  In the knocking process, first, data ahead of the peak position PEAK is linearly corrected in order to eliminate the data level difference at the peak position PEAK (ST61). FIGS. 3B and 3A show the ion current waveform including the correction state, and show a correction line that continues smoothly before and after the second peak position PEAK.

  Next, BPF (band pass filter) processing is executed for data after the peak position PEAK (ST62). This BPF process is a process of extracting a knock signal indicating the occurrence of knocking, and only a signal in a frequency band corresponding to the frequency of the knock signal specified in advance from the structure of the internal combustion engine is extracted.

  Then, it is determined whether knocking has occurred based on the extracted signal (ST63). FIGS. 3B and 3B show knock signals extracted from data after the second peak PEAK, and indicate that knocking has occurred.

  As described above, in this embodiment, the intermediate value MD (i) obtained from the previous and subsequent waveform data is compared with the data value S (i), and the position where the intermediate value MD (i) is much larger is determined. It is the end point of the first peak. The end point of the first peak is a point where the variation amount of the deviation is large, in short, a position where the deviation is suddenly changed from large to small. In the present embodiment, since the position where the deviation suddenly changes in the reverse direction from the final data is searched, the first peak is not erroneously determined as the second peak.

  Further, in the present embodiment, the deviation between the intermediate value MD (i) and the data value S (i) is normalized and compared with the threshold value TH, so that in the operation region where the second peak is small such as a low load. Can accurately detect the second peak.

  In addition, since the BPF process is executed by substantially removing data from the first peak to the second peak, only the target knock signal can be specifically extracted.

  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 ion current detection circuit is merely an example of the simplest circuit configuration, and of course, a more complicated circuit configuration may be adopted.

It is a circuit diagram which shows the structure of the combustion control apparatus which concerns on an Example. It is a time chart explaining operation | movement of the combustion control apparatus of FIG. It is the flowchart and time chart explaining operation | movement of the combustion control apparatus of FIG. It is a flowchart which shows a part of FIG. 3 in detail. It is a time chart explaining the problem of a prior art.

Explanation of symbols

EQ Combustion control device L1 Primary coil L2 Secondary coil CL Ignition coil Q Switching element ECU Control device Vo Detection signal ION Ion current detection circuit ST1 Acquisition means ST4 Search means ST5 Identification means ST6 Control means ST7 Control means

Claims (7)

An ignition coil composed of 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 An ignition plug that performs a discharge operation upon receiving a voltage, and an ion current detection circuit that outputs a detection signal proportional to the ion current indicating the combustion state of the internal combustion engine,
The control device includes:
Obtaining means for obtaining a detection signal when the switching element is in an OFF state;
A search means for analyzing the waveform of the detection signal acquired by the acquisition means, and searching for a trough having a depth greater than or equal to a predetermined depth from the rear to the front of the time axis;
The search means searches the time axis backward from the valley first detected, and specifies the peak position of the waveform of the detection signal;
Control means for executing abnormality determination and / or combustion control based on the identified peak position;
A combustion control apparatus for an internal combustion engine, comprising:   The combustion control apparatus according to claim 1, wherein when the noise component is superimposed on the detection signal, the search means is made to function after removing the noise component. Whether the valley is a predetermined depth or more,
The combustion control device according to claim 1 or 2, wherein the combustion control device is evaluated by a deviation between a level of the detection signal at the specific position and an average value of the levels of the detection signals before and after the specific position.   The combustion control apparatus according to claim 3, wherein the deviation is normalized and then compared with a threshold value. For the detection signal after the convergence of vibration noise generated after the discharge of the spark plug, a cumulative means for calculating a cumulative value over time is provided,
The combustion control apparatus according to claim 4, wherein the deviation is normalized by the accumulated value.   The combustion control device according to any one of claims 1 to 5, wherein it is determined whether or not knocking has occurred.   The combustion control device according to any one of claims 1 to 6, wherein MTB control is realized based on the specified peak position.