JP2013163989A - Combustion control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a knock detecting device that can surely detect the occurrence of knocking regardless of a noise level.SOLUTION: A combustion control device is configured to include: a control device ECU that performs ON/OFF operation of a switching element Q for controlling an ignition coil; and an ion current detection circuit that outputs a detection signal proportional to an ion current. The control device is provided with: knock BPF processing ST1 in which a knock frequency band is set as a pass band; noise BPF processing ST4 in which the knock frequency band is set as a cutoff band while an upper band and a lower band of the knock frequency band are set as pass bands; first smoothing processing ST3 in which each signal value after the knock BPF processing is smoothed within a predetermined range; second smoothing processing ST5 in which each signal value after the noise BPF processing is smoothed within a predetermined range; difference specification processing ST6 in which the operation results of the first smoothing processing and the second smoothing processing are compared with each other to specify a difference value between them; and determination processing ST7-ST8 in which the occurrence of knock is determined based on the difference value.

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 can specifically detect knocking while eliminating the influence of corona noise and the like.

  In general, knocking of an internal combustion engine (hereinafter referred to as “knock”) means an abnormal state in which an explosion generated by a spontaneous ignition (pre-ignition) of an air-fuel mixture collides with an explosion generated by a spark plug and generates a shock wave. To do. It is known that combustion control that quickly eliminates such an abnormal state and protects the internal combustion engine is necessary, and knock generation can be detected based on ions generated during combustion of the air-fuel mixture.

  However, since noise such as corona noise is superimposed on the ion signal at random timing, it is necessary to eliminate these effects and detect only the original ion signal. Techniques have also been proposed.

  For example, in the invention described in Patent Document 4 by the present inventor, (a) BPF processing for an ion signal having a knock frequency as a pass band, and (b) for an ion signal having a frequency band above the knock frequency as a pass band. The HPF process is executed, and the knock value is determined by comparing the integral value of the signal after the BPF process (a) with the integral value of the signal after the HPF process (b). And at the time of knock determination, control such as retarding the ignition timing suppresses the generation of knock noise and prevents engine destruction.

Japanese Patent Laid-Open No. 06-159129 Japanese Patent Laid-Open No. 10-089216 JP-A-10-103210 JP 2011-140881 A

  However, according to further research by the present inventor, any method sometimes erroneously determined that knocking occurred due to corona noise despite normal combustion. Here, since the corona noise is caused by the discharge of the electric charge charged on the spark plug surface, the discharge mode is not uniform, and when the vibration in the knock frequency band occurs with the same intensity, Discrimination was difficult.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a combustion control device that can reliably perform knock determination regardless of the discharge mode of corona noise.

  In order to achieve the above object, as a result of repeating various experiments, the present invention executes the knock BPF process for the knock frequency band and sets the knock frequency band as the cut-off band, It is found that the influence of corona noise can be surely eliminated by executing noise BPF processing with the lower band as the pass band, smoothing the results of knock BPF processing and noise BPF processing appropriately, and taking the difference value. The present invention has been completed.

  That is, the present invention includes 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, An ignition plug that performs a discharge operation upon receiving an induced voltage of the secondary coil; and an ion current detection circuit that outputs a detection signal proportional to an ion current indicating a combustion state of the internal combustion engine, and the control The apparatus includes a knock extraction unit that performs knock BPF processing using a knock frequency band as a pass band for a detection signal in a predetermined data analysis section in which the switching element is in an OFF state, and a knock signal for the detection signal in the data analysis section. A noise BPF process in which the frequency band is a cut-off band and the upper and lower bands of the knock frequency band are passbands. Noise extraction means for performing the above-described processing, first smoothing means for smoothing each signal value after the knock BPF processing based on a predetermined number of signal values continuous before and after itself, and each signal after the noise BPF processing The second smoothing means for smoothing the value based on a predetermined number of signal values consecutively before and after the self, and the calculation result of the first smoothing means and the second smoothing means are compared and the difference value is specified A difference specifying means and a determining means for determining whether or not knocking has occurred based on a difference value specified by the difference specifying means are provided.

  When the present invention is applied to an automobile engine, the control device of the present invention does not necessarily mean an ECU (Engine Control Unit) alone, but a dedicated computer circuit that operates under the control of the ECU, such as a DSP (Digital Signal Processor). It is a concept that includes circuits.

  In the present invention, the pass band of the knock BPF process and / or the noise BPF process (pass band in the designed frequency characteristics) is evaluated at the 20% filter gain position with respect to the BPF center frequency for convenience. When the pass band is defined as described above, it is preferable to set the pass band of the knock BPF to a narrow band of 4 kHz or less.

  Further, in response to such a narrow-band knock BPF process, it is preferable that the noise BPF pass band be brought close to each other so as to overlap both ends of the knock BPF pass band. Then, by bringing the three passbands close to each other, even the weak corona noise can be eliminated. FIG. 1A illustrates the pass band design characteristics of the knock BPF process and the noise BPF process in the embodiment.

  In the case of this embodiment, the center frequency of the knock BPF is 8 kHz. Further, the lower and upper center frequencies of the noise BPF are set to 5.5 kHz and 10.5 kHz, respectively. The pass band of the knock BPF is 6.5 kHz to 9.5 kHz, and the pass band of the noise BPF is 4 kHz to 7 kHz in the lower region and 9 kHz to 12 kHz in the upper region (see FIG. 1B). . That is, in the embodiment, the pass bands of the knock BPF and the noise BPF are all 3 kHz, and the pass band of the noise BPF is overlapped by 0.5 kHz at both ends of the pass band of the knock BPF.

  In the embodiment, the process shown in FIG. 1A is realized by a single process (noise BPF process). However, the process is not necessarily limited, and the BPF in the lower region is divided into two processes. The process and the BPF process in the upper area may be repeated.

  In the present invention, the difference value specified by comparing the calculation results of the first smoothing means and the second smoothing means is preferably the signal value D1 (i) after the smoothing processing of the first smoothing means, and the second The level difference (difference value) from the signal value D2 (i) after the smoothing process of the smoothing means should be accumulated and calculated on the time axis.

  In the present invention, the lower and upper passbands in the noise BPF processing are preferably set close to the knock BPF processing passband, but more preferably, the center frequency FL of the lower passband is The center frequency F0 [kHz] of the knock frequency band should be set to 0.6 * F0 to 0.8 * F0. In this case, the center frequency FH of the upper passband in the noise BPF processing is preferably set to FH = 2 * F0−FL.

  Incidentally, in this embodiment, the center frequency F0 of the knock BPF is 8 kHz, the center frequency FL of the lower noise BPF is 5.5 kHz, and is set to about FL = 0.69 * F0. Further, the center frequency FH of the upper noise BPF is 10.5 kHz, which conforms to the relational expression of FH = 2 * F0−FL.

  By the way, in order to make the passbands of the three BPFs narrow and close to each other, it is desirable that both ends of the passbands have steep frequency characteristics. To realize such frequency characteristics, each BPF process Is preferably composed of an FIR filter having an order M of 30th to 65th.

  The predetermined number of signal values is M * (0.75 to 1.25) signal values with respect to the order M of the FIR filter, and it is more preferable that the number before and after the same is the same. .

  Incidentally, in the embodiment, since the order of the BPF filter is the 53rd order, the first smoothing means adds the self to the 28 data ahead of the time axis and 28 data behind the time axis. The data is smoothed and replaced with its own data. In the second smoothing means, 49 data obtained by adding itself to 24 data ahead of the time axis and 24 data behind the time axis are smoothed and replaced with their own data.

  It has been experimentally confirmed that smoothing within such a range can surely eliminate the influence of random noise at a fine level, and enables accurate extraction of knock signals.

  Further, in order to improve the knock detection accuracy by acquiring a weak knock signal without reading it out, it is preferable to acquire the detection signal at a sampling frequency higher than 30 kHz.

  In addition, it is effective to set the pass bandwidths of the upper region and the lower region in the noise BPF processing to the same width as the design value. The smoothing processing by the first smoothing means and the second smoothing means is performed for each BPF. It is preferable to perform median processing in which the signal value after processing is replaced with a median value in a predetermined time range. In this case, it is preferable that the median value is extracted by evaluating the signal value after each BPF process using its absolute value. In addition, the data analysis section of the present invention includes the position of the second peak of the detection signal indicating that the ignition operation of the internal combustion engine has been completed and the generation of heat has started in earnest, and the region behind the detection signal. Is preferably set in advance to improve detection performance.

  According to the above-described present invention, it is possible to realize a combustion control device that can reliably perform knock determination regardless of the corona noise discharge mode.

It is drawing explaining the frequency characteristic of the BPF process used in an Example. 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 a combustion control apparatus. It is a flowchart explaining operation | movement of a combustion control apparatus.

  Hereinafter, examples will be described in more detail. FIG. 2 is a circuit diagram showing the combustion control device DET according to the embodiment, and FIG. 3 is a time chart showing schematic waveforms of each part of the combustion control device DET.

  As shown in FIG. 2, this combustion control device DET is provided with an ECU (Engine Control Unit) that 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. 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 performs the discharge operation, and the ion signal detection circuit ION. It is configured.

  The output voltage Vo of the ion signal detection circuit ION is supplied to an A / D converter (not shown) of the ECU, and is stored in a memory of the ECU as a digital level ion signal. Here, the output voltage Vo of the ion signal detection circuit ION is acquired in a data acquisition interval from the falling timing of the ignition pulse PLS until the ion current disappears. Then, after all the data is acquired, a knock BPF process and a noise BPF process, which will be described later, are executed in the data analysis section WIN determined for each operation state.

  For this reason, the ECU is provided with a reference table TBL for specifying the data analysis section WIN from the analysis start position A to the analysis end position C for each operating state. The operating state is specified by, for example, the intake pipe pressure of the engine and the engine speed, and the data analysis section WIN is specified by searching the reference table TBL using these as search parameters.

  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 reaches a maximum near the crank angle at which the combustion pressure becomes maximum. And shows the second peak of the ionic current. Here, the waveform near the first peak indicates the behavior of chemical ions at the start of combustion, and the waveform near the second peak seems to indicate the behavior of thermal ions generated by heat generation after the start of combustion. .

  Therefore, in this embodiment, the analysis start position A is experimentally specified so that it is a position slightly before the second peak position of the ion current, and the analysis end position C is a position where the combustion reaction is completed. Thus, it is defined in the reference table TBL of the ECU.

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

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

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

  In the combustion control apparatus DET configured as described above, when the ignition pulse PLS 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 spark plug PG, thereafter, the combustion reaction proceeds rapidly. → Flows along the path of the spark plug PG. Therefore, the output voltage Vo of the ion signal detection circuit ION is Vo = R2 * i, which is a value proportional to the ion current i.

  Next, the operation content of the combustion control device DET will be described based on the flowchart of FIG.

  The ECU lowers the ignition pulse PLS for each ignition cycle (T0), cuts off the current of the primary coil L1, and then digitally converts the output voltage Vo of the ion signal detection circuit ION for the data acquisition period. Then, it is stored in the memory as an ion current detection signal SG (i) (ST1).

  Although the sampling frequency is not particularly limited, in this embodiment, it is set to 50 kHz in order to realize precise knock determination. The data acquisition section ends at the timing when the combustion reaction is surely completed, but this final period is experimentally determined in advance corresponding to the operating state.

  The detection signal SG (i) acquired in the process of step ST1 includes a case where the knock signal is superimposed and shows the behavior of the abnormal combustion state, and a case where the detection signal SG (i) shows the behavior of the normal combustion state without the knock signal being superimposed. is there. In addition to the knock signal, corona noise or the like that is difficult to distinguish from the knock signal may be superimposed regardless of whether the combustion state is appropriate. However, according to the configuration of the present embodiment, only the knock signal can be specifically acquired to correctly determine the combustion state.

  When the processing of step ST1 is completed, the analysis start position A and the analysis end position C are specified for the analysis section WIN = [A, C] corresponding to the current operation state with reference to the reference table TBL. For the analysis section WIN, a knock BPF process using the knock frequency as a pass band is executed (ST2).

  In the case of this embodiment, the knock frequency is experimentally specified in advance as 8 kHz, and the 20% filter gain position with respect to the center frequency 8 kHz of the knock BPF processing is defined as the bandwidth of the knock BPF processing. The bandwidth design value is 3 kHz from 6.5 kHz to 9.5 kHz as shown in FIG. In the embodiment, in order to realize the above-described frequency characteristics, a filter design method using a window function method is employed. Specifically, a 53rd-order (= 2 * X + 1) FIR digital is used using a Hamming window. The filter coefficient is specified. In this digital filter, the impulse response h (n) is symmetrical h {(X + m)} = h {(X−m)} (where m = 0, 1,..., X), and X = 26.

  If the knock BPF process of step ST2 is completed, then the knock median process is executed as the first smoothing process on the absolute value ABS (SG1 (i)) of the data SG1 (i) after the knock BPF process (ST3). ). In the knock median processing of the present embodiment, all the data SG1 (i) after the knock BPF processing is an absolute value data string ABS (SG1 (SG1 ( i−28))... is replaced by the median value D1 (i) of ABS (SG1 (i + 28)).

  That is, in the knock median processing of the present embodiment, the time width D including 28 points preceding each data SG1 (i), 28 points following each data SG1 (i), and the self data SG1 (i). The median value D1 (i) of the 57 pieces of data (absolute value ABS) is specified, and each data SG1 (i) is converted into the median value D1 (i) to be smoothed. Since the sampling period of this embodiment is 20 μS (= 1/50 kHz), the time width D of the knock median processing is 57 × 20 = 1140 μS.

  When the process of step ST3 is completed, next, a noise BPF process is performed in which the knock frequency band is set as an attenuation band and the upper and lower regions of the knock frequency band are set as pass bands (ST4). As shown in FIG. 1A, the noise BPF processing of the embodiment has a bimodal characteristic in which two center frequencies (5.5 kHz, 10.5 kHz) with a filter gain = 1 are provided. An attenuation region with a filter gain of 20% or less is provided between the passbands.

  In the case of the embodiment, the pass band of the bimodal characteristic shown in FIG. 1A is a combination of a lower BPF having a pass band of 6.5 kHz to 9.5 kHz and an upper BPF having a pass band of 9 kHz to 12 kHz. The upper and lower sides have a pass bandwidth of 3 kHz. By adopting such a configuration, it is possible to reliably acquire the components of corona noise that shows a spectral distribution that gently extends in a wide band at a low level as shown in FIG.

  The spectral distribution shown in FIG. 1B is an example of a large number of measured data of corona noise, and the other measured data is common in that it extends smoothly in a wide band at a low level, but a specific spectral shape. Is totally different. Therefore, the significance of the noise BPF processing of the present embodiment in which the knock frequency band is the cut-off band and the upper band and the lower band of the knock frequency band are the pass bands is significant.

  In the embodiment, in order to realize the frequency characteristic of the noise BPF shown in FIG. 1A, a filter design method based on the window function method is employed, and a 53rd order (= 2 * X + 1) is used using a Hamming window. The FIR digital filter coefficient is specified. Also in this digital filter, the impulse response h (n) is symmetrical h {(X + m)} = h {(X−m)} (where m = 0, 1,..., X), and X = 26.

  When the noise BPF process (ST4) is finished, the noise / median process is subsequently executed as the second smoothing process on the absolute value ABS (SG2 (i)) of the data SG2 (i) after the noise BPF process. (ST5). This noise median process is a technique similar to the knock median process, and all the data SG2 (i) after the noise BPF process are absolute value data strings ABS of 49 time widths D (including self). SG2 (i-24))... Is replaced with the median value D2 (i) of ABS (SG2 (i + 24)).

  Next, the result data D1 (i) of the knock median process in step ST3 and the result data D2 (i) of the noise median process in step ST5 are compared on the time axis, and D1 (i)> D2 In the case of (i), the difference value D1 (i) −D2 (i) of the result data of the two median processes is accumulated (ST6). By this difference accumulation process SUM = Σ (D1 (i) −D2 (i)), knock information SUM from which the influence of corona noise and the like is eliminated is extracted.

  Note that since the knock median process and the noise median process are both performed on the absolute value of the data after the BPF process, each result data D1 (in cumulative calculation SUM = ΣD (i) −D2 (i) i) and D2 (i) always indicate positive values.

  Subsequently, the evaluation value X is specified for the detection signal SG (i) in the analysis section [A, C] (ST7). The specific method of specifying the evaluation value X is not particularly limited. For example, for the detection signal SG (i) in the analysis section WIN, an integral value on the time axis is calculated, or the second peak of the ion current is calculated. The position detection signal value PK (ion peak value) is specified as an evaluation value X.

  Then, the evaluation value X specified in the process of step ST7 is substituted into the judgment formula A * X + B, and the substitution result into this judgment formula is compared with the cumulative value SUM calculated in step ST6 (ST8). Here, the judgment formula is a primary formula that defines whether or not the evaluation value X means occurrence of knock, and means a judgment threshold for knock judgment for the evaluation value X. In this determination formula A * X + B, the constants A and B are experimentally specified in advance, and when the cumulative value SUM of the difference values D1 (i) −D2 (i) is large and SUM> A * X + B. It is determined that a knock has occurred.

  When knocking occurs, the internal combustion engine is prevented from being damaged by performing combustion control such as retarding the ignition timing in the next ignition cycle (ST10).

  As described above, in this embodiment, the difference value between the processing results D1 (i) and D2 (i) of the first smoothing process and the second smoothing process is accumulated. Σ (D1 (i) −D2 (i)) By doing so, the influence of corona noise and the like is eliminated, and knock occurrence is specifically determined.

  As mentioned above, although the Example of this invention was described in detail, the concrete description content does not specifically limit this invention. For example, in the embodiment, the simplest circuit configuration is illustrated as the ion signal 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 Ignition plug ION Ion signal detection circuit ST2 Knock BPF means ST4 Noise BPF means ST3 First smoothing means ST5 Second smoothing means ST6 Difference specifying means ST7 to ST8 Determination means

Claims (12)

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 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 controller is
Knock detection means for performing knock BPF processing with a knock frequency band as a pass band for a detection signal in a predetermined data analysis section in which the switching element is in an OFF state;
Noise extraction means for performing noise BPF processing for the detection signal in the data analysis section, with the knock frequency band as a cutoff band while the upper band and lower band of the knock frequency band as pass bands;
First smoothing means for smoothing each signal value after the knock BPF processing based on a predetermined number of signal values continuous before and after itself;
Second smoothing means for smoothing each signal value after the noise BPF processing based on a predetermined number of signal values continuous before and after itself;
A difference specifying means for comparing the calculation results of the first smoothing means and the second smoothing means and specifying the difference value;
Determining means for determining whether or not knocking has occurred based on the difference value specified by the difference specifying means;
A combustion control device characterized by comprising:   When the design characteristics of the pass band of the knock BPF process and the noise BPF process are evaluated at a position of 20% of the pass characteristic at the center frequency of the BPF, the frequency band of the knock BPF process and the noise BPF process is equal to the pass band of the knock BPF. The combustion control device according to claim 1, wherein the combustion control device is provided close to both ends so that the passbands of the noise BPF overlap.   The difference specifying means accumulates the level difference between the signal value after the smoothing process of the first smoothing means and the signal value after the smoothing process of the second smoothing means on the time axis, thereby obtaining the difference value. The combustion control device according to claim 1 or 2 to be specified.   The center frequency FL of the lower band in the noise BPF processing is set to 0.6 * F0 to 0.8 * F0 of the center frequency F0 [kHz] of the knock frequency band. Combustion control device.   The combustion control apparatus according to any one of claims 1 to 4, wherein a center frequency FH of an upper band in the noise BPF processing is set to FH = 2 * F0-FL.   The combustion control apparatus according to any one of claims 1 to 5, wherein each of the BPF processes includes an FIR filter having an order M of 30th order to 65th order.   7. The predetermined number of signal values is M * (0.75 to 1.25) signal values with respect to the order M of the FIR filter, and the number before and after the same is the same. Combustion control device.   The combustion control apparatus according to any one of claims 1 to 7, wherein the detection signal is acquired at a sampling frequency higher than 30 kHz.   The combustion control device according to claim 1, wherein the upper bandwidth and the lower bandwidth pass bandwidth in the noise BPF processing are set to the same width as a design value.   The smoothing processing by the first smoothing means and the second smoothing means is realized by replacing the signal value after each BPF processing with a median value of the predetermined number of signal values. Combustion control device.   The combustion control device according to claim 10, wherein the median value is extracted by evaluating a signal value after each BPF process with an absolute value thereof.   The data analysis section includes a position of the second peak of the ion signal indicating that the ignition operation of the internal combustion engine has ended and heat generation has become serious, and a region behind the ion signal, and is set in advance for each operating state. The combustion control device according to any one of claims 1 to 11.