JP4637038B2 - Knocking control device for internal combustion engine - Google Patents

Description

  The present invention relates to a knocking control device that enables optimal knocking control by accurately extracting a knocking signal in an internal combustion engine such as an automobile engine.

It is generally known that ions are generated when an air-fuel mixture is burned in a combustion chamber of an internal combustion engine. Recently, research on combustion control focusing on the ion current corresponding to this ion has been actively conducted, and an attempt has been made to extract a knock signal superimposed on the ion current and perform combustion control such as retardation control (Patent Literature). 1).
JP 9-338295 A

  This Patent Document 1 discloses a knock intensity detecting means for detecting the strength of knocking generated in an internal combustion engine, an ignition timing retarding means for retarding the engine ignition timing according to the knock intensity during operation, and a response according to the knock intensity during operation. When the engine knock is detected by the valve timing retarding means for retarding the opening / closing timing of the engine intake valve and the knock intensity detecting means, the engine has priority over the ignition timing retarding means when the knock intensity is smaller than a predetermined judgment value. An internal combustion engine knock control device comprising: a valve timing retarding means that operates the ignition timing retarding means in preference to the valve timing retarding means when the valve timing retarding means is greater than or equal to a determination value. Are listed.

  By adopting such a configuration, it is possible to prevent engine damage by suppressing engine knocking, and to minimize the occurrence of engine output decline, fuel consumption deterioration, exhaust temperature rise, etc. It is said to be.

  However, the combustion control as described above is based on the premise that a knock signal can be accurately extracted. If this premise is lacking, the control performance as intended cannot be realized. However, the conventional circuit configuration and extraction method may not be able to accurately extract the knock signal.

  FIG. 8 shows an example of a conventional circuit configuration for extracting a knock signal. This knock signal extraction circuit includes an ion current detection circuit 50 provided between the secondary side of the ignition coil and the spark plug, and a one-chip microcomputer 51 that extracts a knock signal from the detection signal SG of the ion current detection circuit 50. It is structured at the center. The one-chip microcomputer 51 has a built-in AD converter (AD converter), and extracts a knock signal by subjecting the detection signal SG of the ion current detection circuit 50 to BPF (Band Pass Filter) processing. Note that the ion current detection circuit 50 has, for example, the same circuit configuration as that of FIG. 1, and a detection signal SG proportional to the ion current is obtained. In addition, a sample-and-hold (S & H) circuit that holds the detection signal SG at a constant value during the sampling period τ is provided in the preceding stage of the AD converter.

  As shown in FIG. 8, the ion current is generated with a predetermined time delay from the ignition pulse in accordance with the engine operating conditions. When a knocking phenomenon occurs, a knock signal is superimposed on the ionic current drop. Therefore, an extraction window Win having an appropriate time width is determined in advance, and a detection signal SG in the extraction window Win is acquired by AD conversion, and BPF processing corresponding to the frequency of the knock signal is performed on the acquired data. Has been given. That is, since the frequency of the knock signal is specified in advance according to the structure of the internal combustion engine, the knock signal can be extracted by BPF processing corresponding to the frequency of the knock signal.

  However, since the positional relationship between the detection signal SG of the ion current detection circuit and the extraction window Win varies irregularly depending on the operating conditions of the engine, a sudden rising portion as shown in the figure is formed at the head of the window Win. If it is included, this part greatly affects the BPF processing and cannot be distinguished from the original knock signal. Note that it is possible to perform LPF (Low Pass Filter) processing by hardware or software in order to eliminate the sudden rise part, but in this case, the extraction window Win is appropriate and the sudden rise part is removed. In a normal state that does not include, the original knock signal is blunted by LPF processing, and the knock signal cannot be extracted accurately.

  The present invention has been made in view of these problems, and an object thereof is to provide a knock control device for an internal combustion engine that can accurately extract only a knock signal.

In order to achieve the above object, the knocking control apparatus for an internal combustion engine according to the present invention is configured to increase the secondary coil high voltage generated when the primary coil current of the ignition coil in which the primary coil and the secondary coil are electromagnetically coupled is cut off. Based on the above, in an internal combustion engine in which the spark plug is ignited and discharged, and the air-fuel mixture in the combustion chamber is combusted, a signal detection unit for detecting an ion current corresponding to ions generated in the combustion chamber at the time of combustion of the air-fuel mixture is provided. a detection signal after ignition discharge section outputs, a signal input data in a predetermined cut window obtained for each sampling period and differential operation, whether the operation result exceeds a predetermined value binary manner The first means for storing the determination result FG (i) , the determination result FG (i) by the first means is evaluated in the negative direction on the time axis, and each determination result FG (i) First The second means for determining whether the level is the bell or the second level, and when the second means determines that the first level is reached, the first continuous number of the first level determination is increased to increase the first The second means for determining the second level when the second means determines that the second number is the third means for storing the continuous number as the evaluation value CT (i) for the determination result FG (i). Either the continuous number or the third continuous number whose evaluation value has not changed continuously is evaluated, and if the continuous number does not exceed the limit value, the first continuous number is maintained, while the limit value is maintained. A fourth means for returning the first continuous number to the initial value when the value exceeds the initial value and storing the first continuous number maintained or returned to the initial value as the evaluation value CT (i) for the determination result FG (i); , Corresponding to the maximum value CT (X) among all evaluation values CT (1) to CT (N) 5th means for specifying the time position of the signal input data as the peak position, and after correcting the signal input data before the peak position specified by the 5th means, the corrected signal input data is filtered and knocked It is configured to include a sixth means for extracting a signal.

Here, it is preferable that the seventh means matches all the previous signal input data with the level of the signal input data at the peak position based on the peak position specified by the sixth means .

  In the present invention, the limit value is typically determined in accordance with the knock frequency determined based on the structure of the internal combustion engine. Further, the present invention provides a data table for specifying a relationship between an operating condition of an internal combustion engine and an ionic current generated under the operating condition, and the data table is set based on a dynamically changing operating condition. It is effective to realize the differential operation by referring to the fundamental wave period of the ionic current at that time and executing the difference operation with the difference time width determined corresponding to the grasped fundamental wave period. It is.

  According to the present invention described above, it is possible to realize a knocking control device that can always accurately extract a knock signal regardless of fluctuations in the operating state of the internal combustion engine. That is, until the ion current reaches the peak value, the level is maintained at a constant value, so that a sudden rising portion does not occur in the region of the BPF process, and only the knock signal can always be extracted.

  Hereinafter, the present invention will be described in detail based on examples.

  FIG. 1A is a circuit diagram illustrating a knock control device EQU for an internal combustion engine according to an embodiment. This knocking control unit EQU is connected to an ignition coil 1 in which a primary coil 1P and a secondary coil 1S are electromagnetically coupled, a switching transistor 2 that intermittently drives the ignition coil 1, and a secondary coil 1S of the ignition coil. And the one-chip microcomputer 4 that controls the ON / OFF of the switching transistor 2 and receives the analog detection signal SG from the ion current detection circuit 3. A spark plug 5 is connected between the secondary coil 1S of the ignition coil and the ground line.

  As shown, the base terminal of the switching transistor 2 is connected to the one-chip microcomputer 4, the collector terminal is connected to the primary coil 1P of the ignition coil, and the emitter terminal is connected to the ground line.

  The ion current detection circuit 3 includes a bias capacitor C that is charged by the discharge current of the spark plug 5, a chainer diode ZD that is connected in parallel to the capacitor C and regulates the charging voltage of the capacitor C, and a chainer diode ZD. The diode D1 is connected in series, and the amplification unit AMP is connected to both ends of the diode D1.

  The anode terminals of the Zener diode ZD and the diode D1 are directly connected to each other, and the cathode terminal of the diode D1 is connected to the ground line. The cathode terminal of the Zener diode ZD is connected to the secondary coil 1S.

  The amplification unit AMP of the ion current detection circuit 3 includes an amplification element Q1 having an inverting terminal, a non-inverting terminal, and an output terminal, an input resistor R1 connected to the inverting terminal of the amplification element Q1, and an inverting terminal of the amplification element Q1. The feedback resistor R2 is connected between the output terminals. A diode D2 for protecting the amplifying element Q1 may be connected between the inverting terminal of the amplifying element Q1 and the ground line.

  In this embodiment, an OP amplifier is used as the amplifying element Q1. The input impedance of the OP amplifier is almost infinite (≈∞), and the inverting terminal and the non-inverting terminal are virtually short-circuited (imaginary short). Therefore, the current I shown in FIG. 1B flows in common to the input resistor R1 and the feedback resistor R2, and the output voltage Vout of the amplifier AMP is the product of the current I and the feedback resistor R2 (Vout = I * R2). That is, in this amplification unit AMP, the feedback resistor R2 functions as a detection resistor for the input current I.

  In the circuit configuration of FIG. 1, when a negative high voltage is generated in the secondary coil 1S, the spark plug 5 is ignited and the ignition current charges the capacitor C as shown in FIG. At this time, since the Zener diode ZD is connected in parallel to the capacitor C, the voltage across the capacitor C matches the breakdown voltage Vz of the Zener diode ZD. During this discharge, the diode D1 is short-circuited (ON), so that the current flowing through the input resistor R1 and other circuit elements can be ignored.

  After that, when the high voltage of the secondary coil 1S disappears (see FIG. 1D), the bias voltage charged in the capacitor C is discharged through the path shown in FIG. This discharge current is nothing but the ionic current I (see FIG. 1 (e)). The ionic current I is the output terminal of the amplifying element Q1, the feedback resistance R2, the input resistance R1, the capacitor C, the secondary coil 1S, and the ignition. It flows through the path of the plug 5. As described above, since the relationship of the output voltage Vout = R2 × I is established, a voltage proportional to the ion current I is obtained from the amplifying unit AMP.

  The one-chip microcomputer 4 includes a CPU core 4a, an A / D converter 4b, an output port 4c, and a memory unit 4d. The A / D converter 4b directly receives the analog detection signal SG from the ion current detection circuit 3 and converts it into digital data. Further, an ignition pulse is output from the output port 4 c toward the base terminal of the switching transistor 2. In the illustrated knocking control device EQU, the ion current detection circuit 3 and the one-chip microcomputer 4 are directly connected, but a sample hold circuit or the like may be provided in the middle.

  When the knock signal is extracted with the circuit configuration as described above, the knock signal generally exists in a level drop region after the peak position of the ion current, and therefore it is important to accurately extract the peak position. However, even if the peak position is simply obtained from the differential value of the input signal SG, the peak position of the knock signal and other peak positions are extracted, so that only the peak position of the ion current is specifically extracted. It is not possible. Therefore, in this embodiment, as shown in the flowchart of FIG. 2A, the peak position of the ion current is accurately extracted by a specific difference calculation (differential calculation) and a special count calculation (ST1 to ST1). ST5). The extracted data before the peak position is subjected to BPF processing assuming that the peak value is constantly maintained (ST6). Therefore, a knock signal can be accurately extracted regardless of the start position of the BPF process.

  Specifically, as shown in FIGS. 1 and 2A, first, the one-chip microcomputer 4 receives the analog detection signal SG obtained from the ion current detection circuit 3 directly by the A / D converter 4b. The digitally converted data is stored in the memory unit 4d (ST1). The sampling frequency at the time of data acquisition is set to about 30 KHz, for example, and in this embodiment, the sampling period τ is 33 μS. The actually acquired data is data in a range (T + α) that is slightly wider than the range (T) of the cut window Win shown in FIG. 2B, but for convenience of explanation, FIG. All the data of +25 mS from the falling timing of the ignition pulse (t = 0) are shown.

  If the data acquisition of the necessary range is completed by the processing of step ST1 in FIG. 2A, next, the N signal input data S (i) in the extraction window Win stored in the memory unit 4d will be represented by D (i ) <-Differentiation is performed by the difference calculation of S (i) -S (ia) (ST2). Here, the position of the cutout window Win and its time width T (= 33 μS × (N−1)) are set so that the generated ionic current can be reliably captured.

  The ion current is generated after the discharge of the spark plug 5 is completed (see FIG. 1 (e)). The discharge timing of the spark plug 5 and the disappearance timing of the generated ion current are determined by the operation such as the engine speed and the engine load. It changes dynamically according to conditions. Therefore, in this embodiment, a relationship between the operating condition and the generated ion current is experimentally obtained in advance, and a window calculation table TBL1 indicating the relationship is provided in the memory unit 4d. In actual operation, the window calculation table TBL1 is searched based on data obtained from various sensors, and the start position and end position of the cut window Win are determined in real time based on the search result.

  FIG. 2B illustrates the relationship between the analog signal waveform obtained from the ion current detection circuit and the cut-out window of the time width T. Here, the ignition pulse falling timing (t = 0) is shown. A range from +4 mS to +15 mS is cut out as a reference, and is defined as a win-win.

As shown in the flowchart of FIG. 3A, the differentiation process (ST2) of FIG. 2A performs D (i) ← S (i) for N data S (i) of i = 1. ) -S (ia) is executed (ST21 to ST23). FIG. 3B illustrates an analog detection signal SG (original waveform) obtained from the ion current detection circuit and a differential waveform obtained by differential calculation. The differential processing means obtaining the difference of the time interval a × τ for the N pieces of data in the extraction window. The difference time interval a × τ is the basic period τ of the knock signal superimposed on the ion current. _Although it is longer than _n, it is set shorter than the fundamental wave period W ₀ of the ion current (W _n <a × τ <W ₀ ). By executing the differential processing using such a difference time interval a × τ, it is possible to grasp the overall increase / decrease tendency of the ion current waveform by eliminating the influence of the knock signal superimposed on the ion current.

By the way, the fundamental frequency F = 1 / W ₀ of the ionic current dynamically changes according to operating conditions such as the engine speed and the engine load. Therefore, in this embodiment, a data table TBL2 indicating the relationship between the operating condition and the fundamental wave period W ₀ of the ion current is provided in the memory unit 4d, and the time interval satisfying the above-described condition of W _n <a × τ <W ₀ is satisfied. a × τ is determined in real time.

However, not only a knock signal but also other high-frequency noise may be superimposed on the ion current. Therefore, in order to eliminate the influence of the knock signal including the high-frequency noise superimposed on the ion current, the value of the time interval a × τ is set to the fundamental wave of the ion current regardless of the magnitude of the fundamental period τ _n of the knock signal. It is preferable to set a value slightly shorter than the period W ₀ (= W ₀ −β). In the illustrated example, since the fundamental frequency of the ion current of about 2.5 KHz is expected from the operating condition, a value satisfying the relationship of a × τ <400 μS is set to a = 10, and the difference time interval a × τ is set to 330 μS. I have to.

  When the differentiation process in step ST2 in FIG. 2A is completed, the differentiation value D (i) is compared with the differentiation threshold value TH to calculate a differentiation result flag FG (i) (ST3). FIG. 4A is a flowchart showing the specific contents of the determination process, and FIG. 4B shows a differential waveform indicating the transition of the differential value D (i) and a differential result flag calculated from the differential waveform. The relationship with FG (i) is illustrated.

  As shown in steps ST32 to ST34 in FIG. 4A, if the differential value D (i) is greater than or equal to the differential threshold TH for N data of the variable i = 1... N, the differential result flag FG (i). FG (i) = 0, and conversely, if the differential value D (i) is less than the differential threshold TH, the differential result flag FG (i) is set to FG (i) = 1. Here, the threshold value TH is set as appropriate, but it is usually sufficient that TH = 0.

  When the threshold value TH = 0 is set, the differential result flag FG (i) is set by the determination process (ST3) in a time zone in which the analog signal waveform SG is increasing in the time axis direction (D (i)> 0). On the contrary, the differential result flag FG (i) becomes 1 in the time zone in which the analog signal waveform SG has a decreasing tendency (D (i) <0) in the time axis direction.

  In any case, once the differential result flag FG (i) is calculated by the process of step ST3 in FIG. 2A, next, the N differential result flags FG (i) are reversed on the time axis ( In other words, a special count process is performed (in descending order from FG (N) to FG (1)) (ST4 in FIG. 2).

  As shown in FIG. 5 (a), in this counting process, first, all areas of the counter variable CT are cleared to zero (ST41), and then, starting from i = N, the time axis is reversed until i = 1. The processing of ST43 to ST48 is executed. Here, the time axis is processed in the reverse direction because (a) the knock signal exists from the peak position of the ion current waveform to the end of the waveform, and (b) from the engine ignition to the peak position of the ion current. This is because the waveform up to this point is relatively apt to be disturbed, so that processing in the positive direction on the time axis increases the possibility of erroneously detecting the peak position of the ion current.

  The process of steps ST43 to ST48 shown in FIG. 5A will be specifically described. In the process for the variable i, first, it is determined whether or not the value of the differentiation result flag FG (i) is 1 (ST43). If the differentiation result flag FG (i) is 1, the counter value CT (i) is converted to the counter value CT (i + 1) on the time axis by the calculation of CT (i) ← CT (i + 1) +1. Is increased by one (ST47). On the other hand, if the differentiation result flag FG (i) is 0, the counter value CT (i + 1), CT is above the time axis variable i on the time axis and has a reference width b of a pulse width (skip width) to be described later. It is determined whether (i + 2),..., CT (i + b) are the same value (ST44).

  If all the counter values are the same, the counter value CT (i) is cleared to zero (ST45). Conversely, if there is a counter value that does not match, CT (i) ← CT (i + 1) is calculated. The counter value CT (i) is set to the same value as the counter value CT (i + 1) that is one higher (ST46).

  In the algorithm of FIG. 5A, the reference width b (b × τ in terms of time) of the pulse width (skip width) is a time for eliminating the influence of the knock signal when detecting the peak position of the ion current. Width, determined based on the fundamental period of the knock signal. In this embodiment, since the frequency of the knock signal is specified as about 7 KHz from the structure of the internal combustion engine, b = 3 is set to eliminate the influence of the knock signal. In this case, when the reference width b = 3 is converted into time, b × τ = 66 μS, and when one period 66 × 2 μS is converted into frequency, it is about 5 KHz, and the influence of unnecessary components of 5 KHz or more including noise components can be eliminated. become.

  FIG. 5B is a diagram for explaining the algorithm of FIG. 5A when the reference width b of the pulse width (skip width) is set to b = 3, and is secured in the memory unit 4d. A differential result flag area FG and a counter area CT are shown. When b = 3 is set, the value of the differential result flag FG (i) becomes a problem when determining the value of the counter area CT (i) (ST43). If FG (i) = 0, The values of CT (i + 1), CT (i + 2), and CT (i + 3) become a problem. If all values are the same, the zero-cleared value is stored in the counter area CT (i) (ST45). If the values of CT (i + 1), CT (i + 2), and CT (i + 3) do not match, the value of CT (i + 1) is stored as it is in the counter area CT (i) (ST46).

  As described above, in this algorithm, the counter value is incremented (+1) only when the differentiation result flag FG (i) = 1. As described above, the differential result flag FG (i) = 1 means that the differential value D (i) of the time interval a × τ is smaller than the threshold value TH (D (i) <TH). In the present embodiment in which the threshold value TH = 0 is set, the differential result flag FG (i) = 1 means that the differential value D (i) in the positive direction of the time axis is negative.

  In any case, in this embodiment, a special count operation is performed from the top to the bottom on the time axis, and the counter value is incremented (+1) only when the differentiation result flag FG (i) is 1. If the differentiation result flag FG (i) is 0, the counter value is not changed unless it continues for the reference width b, and if FG (i) = 0 continuously over the reference width b. In this case, the counter value is cleared to zero. Therefore, the state in which the original waveform monotonously increases in the reverse direction on the time axis is calculated by the counter value, and even if there is a part that increases or decreases in the middle like a knock signal, this will be skipped. And only gentle peaks are extracted.

  Now, returning to FIG. 2 and continuing the description, in the process of step ST5 in FIG. 2A, the maximum value is extracted from each numerical value of the counter areas CT (1) to CT (N), and the maximum value is calculated. The peak position PK of the ion current is specified from the indicated counter position. Since the peak position i = PK of the ionic current is accurately specified by the processing of steps ST1 to ST5, all the signal input data S (i) before the peak position of the ionic current (i <PK) It is rewritten to the level S (PK) of the signal input data at the peak position (ST6). That is, a rewrite operation of S (i) ← S (PK) is executed for each data of i = 1 to PK-1. As a result, the signal input data S (i) becomes a DC value S (PK) that does not include an AC component from i = 1 to PK.

  In this embodiment, the BPF process is performed after performing such a correction calculation (ST6). Therefore, unlike the prior art, there can be no problem that the signal input data S (i) suddenly rises at the start point of the extraction window Win, and only the knock signal can be accurately extracted by the normal BPF processing. It becomes possible. That is, the knocking level can be specified based on the integral value of the BPF output.

  7A shows an ignition pulse for discharging the spark plug, FIG. 7B shows a detection signal SG of the ion current detection circuit 3, FIG. 7C shows signal input data after the correction processing in step ST6, and FIG. d) shows knock signals extracted by the BPF process in step ST6. As shown in FIGS. 7A to 7D, only the knock signal is specifically detected regardless of the suitability of the extraction window Win.

  As described above, according to the present embodiment, only necessary knock signals can be accurately extracted. The specific contents described above do not particularly limit the present invention, and various modifications can be made without departing from the spirit of the present invention. For example, FIG. 6 exemplifies another algorithm for the special count processing. When the differentiation result flag FG (i) = 0, b−1 differentiation flags FG (i + 1), It is determined whether FG (i + 2)... FG (i + b-1) is all zero (ST44). Also in this case, processing substantially similar to that in the case of FIG. 5 is executed, and the peak position of the ion current can be accurately extracted.

It is a circuit diagram which shows the circuit structure of the knocking control apparatus which concerns on an Example. It is the flowchart which shows the outline | summary of control operation of a one-chip microcomputer, and the detection signal waveform of an ion current detection circuit. It is the flowchart which shows a differentiation process, and the wave form diagram of a differentiation waveform. It is a flowchart which shows a determination process, and a drawing which shows a differentiation result flag and a count calculation result. It is drawing which shows the flowchart which shows a counter process, and a count algorithm. It is drawing explaining another count process. It is a time chart explaining a series of operation | movement in the apparatus of an Example. It is drawing explaining the problem of a prior art.

Explanation of symbols

EQ knocking control device 3 Signal detection unit (ion current detection circuit)
ST1 to ST3 Data determination unit ST4 to ST5 Peak identification unit ST6 Signal extraction unit

Claims (5)

An internal combustion engine that burns an air-fuel mixture in a combustion chamber by causing a spark plug to ignite and discharge based on a high voltage of a secondary coil generated when a primary coil current of an ignition coil electromagnetically coupled to a primary coil and a secondary coil is interrupted In
While providing a signal detection unit for detecting an ion current corresponding to ions generated in the combustion chamber during the combustion of the air-fuel mixture ,
It is a detection signal after ignition discharge output from the signal detection unit, which performs differential operation on signal input data in a predetermined cutout window acquired at each sampling period , and determines whether the calculation result exceeds a predetermined value. A first means for determining the value and storing the determination result FG (i);
A second means for evaluating the determination result FG (i) by the first means in the negative direction on the time axis and determining whether each determination result FG (i) is the first level or the second level;
When it is determined by the second means that it is the first level, the first continuous number of the first level determination is increased, and the first continuous number after the increase is an evaluation value for the determination result FG (i). Third means for storing as CT (i);
When the second means determines that it is the second level, it evaluates either the second continuous number of the second level determination or the third continuous number in which the evaluation value does not continuously change, When these continuous numbers do not exceed the limit value, the first continuous number is maintained, while when the limit value is exceeded, the first continuous number is returned to the initial value and maintained or returned to the initial value. 4th means which memorize | stores a number as evaluation value CT (i) about the said determination result FG (i),
Fifth means for specifying the time position of the signal input data corresponding to the maximum value CT (X) among all the evaluation values CT (1) to CT (N) as the peak position;
An internal combustion engine comprising: sixth means for correcting the signal input data before the peak position specified by the fifth means and filtering the signal input data after correction to extract a knock signal; Knocking control device. 7. The knocking control apparatus according to claim 1, wherein the seventh means matches all the previous signal input data with the level of the signal input data at the peak position based on the peak position specified by the sixth means . The knock control device according to claim 1 or 2 , wherein the limit value is determined in accordance with a knock frequency determined based on a structure of the internal combustion engine. Prepare a data table that identifies the relationship between the operating conditions of the internal combustion engine and the ionic current generated under the operating conditions, refer to the data table based on the dynamically changing operating conditions, and then the ionic current at that time to grasp the fundamental period of the, according to any one of claims 1 to 3 in which the second means by a difference time width which is determined in accordance with the fundamental period grasped performing a difference operation realizes the differential operation Knocking control device. The knocking control device according to any one of claims 1 to 4 , wherein the filter process is a BPF process.