JP2005090250A - Engine knock control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect occurrence of knocking with high accuracy using vibration analysis by a frequency conversion means such as an FFT. <P>SOLUTION: Window FFT is performed with respect to a combustion pressure waveform to calculate oscillation strength FFTi of combustion pressure (=Pcyl) in each window. The maximum window (=w2) out of the calculated FFTi is identified, and an analysis period is set so that the timing corresponding to the window is set as start timing. The length of the analysis period is set depending on engine speed. The higher the engine speed is, longer the overlap of the window becomes. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an engine knock control device, and more particularly, to a technique for suppressing knocking based on a result of knock determination by vibration analysis using fast Fourier transform (hereinafter referred to as “FFT”) or the like.

The following are known engine knock control devices. A predetermined analysis period is set for the crank angle, and during this analysis period, the combustion pressure is detected, and it is determined whether knocking has occurred in the engine based on the vibration component of the detected combustion pressure. (Patent Document 1). It is also known to suppress the knocking by delaying the ignition timing when it is determined that knocking has occurred. It is also known that knock determination is performed by vibration analysis using FFT. That is, the combustion pressure waveform is divided into predetermined time zones, and the vibration component of the combustion pressure in each time zone is sequentially analyzed by FFT. Of the obtained frequency spectrum, the level of the frequency band set as indicating the characteristic of knocking is calculated, and this is detected as the vibration intensity of the knocking sound in that period band. The detected vibration intensity is integrated over the entire analysis period, and it is determined whether knocking has occurred based on the magnitude of the integrated value.
JP 09-1226039 A (paragraph numbers 0047 to 0049)

  However, knock determination by the above vibration analysis has the following problems. That is, the analysis period of the combustion pressure is always set to the same time with respect to the crank angle (for example, 10 to 60 ° after the top dead center), and the occurrence of knocking is determined based on the combustion pressure detected during such a fixed analysis period. It is to be done. Of the combustion pressure waveform, the waveform portion containing a loud knocking sound can be detected at various times depending on various conditions. However, there is a margin to ensure that such a waveform portion is the subject of analysis. Therefore, it is necessary to set a long analysis period. When the analysis period is set to be long as described above, a waveform portion that is not necessary for knock determination and that has a relatively small knock sound is also analyzed, and noise components other than the knock sound included in the waveform portion are analyzed. Will also be reflected in the knock determination. For this reason, when knock determination is performed by comparison with the threshold value, it is necessary to set the threshold value to be larger because the noise component is large, and the occurrence of knocking can be detected easily and reliably. It was not limited.

  The present invention identifies a portion of the combustion pressure waveform that contains a large knock noise or has a high probability of occurrence, and sets the optimal analysis period for each knock determination according to the result, thereby generating knocking. The purpose is to detect the occurrence of knocking easily and reliably, and to suppress the generated knocking.

  The present invention provides an apparatus for detecting the occurrence of knocking in an engine and suppressing the generated knocking. The apparatus according to the present invention detects a combustion pressure including a vibration component in a first period set in advance as a period starting from a predetermined crank angle position, and performs knocking based on the detected combustion pressure. The vibration intensity of a frequency band (hereinafter referred to as “characteristic frequency band”) set as a characteristic is calculated in time series. Then, based on the calculated vibration intensity, a second period shorter than the first period and included in the first period is set, and the vibration intensity in the characteristic frequency band is set for the set second period. Whether or not knocking has occurred in the engine is determined based on the calculated at least one vibration intensity. When it is determined that knocking has occurred, control is performed to suppress the generated knocking. As such control, it is preferable to delay the ignition timing.

  According to the present invention, in the first period, the vibration intensity of the characteristic frequency band is calculated in time series, and the second period is set as a substantial analysis period based on the calculated vibration intensity. It was. For this reason, in determining knocking, after grasping the tendency of the entire combustion pressure waveform based on the vibration intensity calculated in chronological order, the optimum second sound corresponding to the waveform portion that contains a large knocking noise or has a high probability of it. Since the period can be set, the influence of the noise component can be kept relatively small, and the determination accuracy can be improved.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows the configuration of an automobile engine (hereinafter referred to as “engine”) 1 including a knock control device according to an embodiment of the present invention.
The engine 1 is a direct injection engine. A throttle valve 12 is installed in the intake passage 11. The flow rate of the intake air is adjusted by the throttle valve 12 and flows into the cylinder while the intake valve 14 is open. An air flow meter 13 is installed upstream of the throttle valve 12. The flow rate of the intake air is detected by the air flow meter 13. The main body of the engine 1 is provided with an injector 15 and a spark plug 16 facing the combustion chamber. An amount of fuel corresponding to the operating state is injected from the injector 15 to the intake air, and the formed air-fuel mixture is ignited by the spark plug 16. The exhaust gas is discharged to the exhaust passage 18 during the open period of the exhaust valve 17. A crank angle sensor 19 and a coolant temperature sensor 20 are installed in the main body of the engine 1, and an in-cylinder pressure sensor 21 is installed. The detection signal of the crank angle sensor 19 is used for calculating the engine speed Ne in the control unit 22 described below. The in-cylinder pressure sensor 21 is configured to include a piezoelectric element that is sensitive to a vibration component of pressure, and a so-called knock sensor can be employed as such. Detection signals from the air flow meter 13, the crank angle sensor 19, the coolant temperature sensor 20, and the in-cylinder pressure sensor 21 are output to the control unit 22. The control unit 22 calculates the fuel injection amount and the ignition timing according to normal conditions based on the input signal, and operates the injector 15 and the spark plug 16 according to the calculation result. Further, the control unit 22 determines whether or not knocking has occurred in the engine 1 as described below, and when it is determined that knocking has occurred, as a control for suppressing the generated knocking, The ignition timing is delayed with respect to the above calculation result.

Next, the configuration of the control unit 22 will be described with reference to the block diagram shown in FIG.
In the block (hereinafter abbreviated as “B” in the description of FIG. 2) 1, the output of the in-cylinder pressure sensor 21 is adapted to the dynamic range of the AD converter.
In B2, the AD converter in the control unit 22 is operated to convert the analog cylinder pressure Pcyl into a digital value. Conversion to a digital value is performed during the detection period (corresponding to “first period”) set in B3.

In B3, the detection period is set to 10 to 60 ° at a crank angle after top dead center (hereinafter referred to as “ATDC”).
In B4, the digital value in-cylinder pressure Pcyl is subjected to FFT processing. The FFT process is performed for each window by dividing the detection period into a plurality of windows. By the FFT process, the levels of the five resonance modes (hereinafter referred to as “vibration intensity”) calculated by the following draper equation (1) are calculated corresponding to each of the characteristic frequency bands. In equation (1), fi (i = 1 to 5) is the resonance frequency for each mode, C is the atmospheric sound velocity, B is the cylinder bore diameter, and ρmn is the coefficient for each mode. The mode-specific coefficient ρmn is set to a value corresponding to the form of the resonance mode (FIG. 3), the subscript m indicates the order of radial vibration, and n indicates the order of circumferential vibration. The result of the FFT process is stored in a storage device in the control unit 22.

fi = C × ρmn / (π × B) (1)
In B5, based on the result of the FFT process, the frequency-specific strength KDLi of the in-cylinder pressure is calculated. The frequency-specific strength KDLi is calculated by integrating the vibration strength FFTi (i = 1 to 5) obtained by the FFT processing for each resonance frequency. Here, the vibration intensity FFTi is integrated only for the window corresponding to the window included in the analysis period (corresponding to the “second period”) set in B6.

In B6, an analysis period is set. The analysis period length Tgate is set according to the engine speed Ne, and the start period of the analysis period is set according to the vibration intensity FFTi. The analysis period length Tgate is set such that the crank angle is shortened as the engine speed Ne increases.
In B7, the background level BGL is calculated. In the present embodiment, the weighted average value KDLavei of the intensity by frequency is set as the background level BGL.

In S8, a difference ΔKDLi between the frequency-specific intensity KDLi and the background level BGL is calculated.
In B9, the difference ΔKDLi is compared with the threshold value SLi set in B10, and when the difference ΔKDLi is larger, it is determined that knocking has occurred in the engine 1.
In B10, the threshold value SLi is set to a value corresponding to the engine speed Ne.

  In B11, when the occurrence of knocking is detected, in order to suppress the generated knocking, the ignition timing is set to be delayed by a predetermined crank angle with respect to the normal value, and thereafter the ignition timing is gradually advanced. Do. For example, after the occurrence of knocking is detected, the ignition timing is delayed at a stretch by a relatively large first angle, and then advanced by a second angle smaller than the first angle per predetermined time.

Next, the operation of the control unit 22 will be described with reference to the flowcharts shown in FIGS.
FIG. 4 is a flowchart of the vibration intensity calculation routine. This routine is executed for the corresponding cylinder j at the detection start interrupt timing (= ATDC 10 °) shown in FIG. In the following description, the cylinder number (for example, 1 to 4) is represented by j.

In S101, initialization processing is performed.
In S102, the AD converter is operated to start conversion of the in-cylinder pressure Pcyl into a digital value.
In S103, the converted in-cylinder pressure Pcyl is sampled. Here, the number of data Nsmp to be sampled in one FFT process is set to 64.

In S104, it is determined whether or not the engine speed Ne is higher than a predetermined value Ne1. When it is higher than Ne1, the process proceeds to S105, and when it is equal to or less than Ne1, the process proceeds to S106. Ne1 is set to, for example, 3000 rpm as the engine speed that separates the low rotation range and the high rotation range.
In S105, it is determined whether or not the number of samples in the current window is a predetermined value Nh. When it is Nh, it progresses to S107, and when it is not Nh, it progresses to S108. Nh is set to 16, for example, as a value having a predetermined value Nsmp as a multiple.

In S106, it is determined whether or not the number of samples in the current window is a predetermined value Nl. When it is Nl, it progresses to S107, and when it is not Nl, it progresses to S108. Nl has a predetermined value Nsmp as a multiple and is set to 64, for example, as a value larger than Nh.
In S107, the next window is activated and sampling by that window is started. That is, in the present embodiment, when the engine speed Ne is higher than Ne1, when the number of samples reaches Nh (= 16), sampling by the next window is started to overlap the windows. I am going to do that. On the other hand, the window is not overlapped by setting the predetermined value Nl for the low rotation to 64 equal to the predetermined value Nsmp.

In S108, it is determined whether or not the number of samples has reached a predetermined value Nsmp. When Nsmp has been reached, the process proceeds to S109, and when it has not reached, the process returns to S103 and sampling of the in-cylinder pressure Pcyl is continued.
In S109, the sampled 64 in-cylinder pressures Pcyl are subjected to FFT processing to calculate the vibration intensity FFTi for each resonance frequency.

In S110, the calculated vibration intensity FFTi is stored in the storage device.
In S111, the number n of FFT processes executed in the current knock determination is incremented by one.
In S112, it is determined whether or not the FFT execution count n after counting up has reached a predetermined value Nmax. When Nmax is reached, this routine is terminated. When it is not reached, the routine returns to S103, and the in-cylinder pressure Pcyl is sampled by the next window. Nmax is set to the maximum value of the number of windows that can be accommodated in the detection period (= ATDC 10 to 60 °).

FIG. 5 is a flowchart of a knock determination routine. This routine is executed for the corresponding cylinder j at the detection end interrupt timing (= ATDC 60 °) shown in FIG.
In S201, the AD converter is stopped and the conversion of the in-cylinder pressure Pcyl into a digital value is completed.

  In S202, the length Tgate of the analysis period is set. The Tgate is set by searching the table shown in FIG. 8 based on the engine speed Ne, and the higher the Ne, the shorter the crank angle is set. In the present embodiment, for ease of handling, the length of the analysis period is set as the number of FFT executions. When Ne is higher than a predetermined value Ne1, Tgate = Tgate1, and when Ne1 or less, Set Tgate = Tgate2 (> Tgate1). In this embodiment, when Ne is higher than the predetermined value Ne1, Tgate is set to a fixed length (= Tgate1). Instead of such setting, the difference between Ne and Ne1 (= Ne). According to -Ne1), Tgate may be shortened in multiple steps from Tgate2 to Tgate1 as the difference is larger.

In S203, the count values m and MAX are both set to 1.
In S204, one count value m is incremented by one.
In S205, it is determined whether or not the vibration intensity FFTi (m) obtained by the m-th FFT process is larger than the vibration intensity FFTi (MAX) obtained by the MAX-th FFT process. When it is larger than FFTi (MAX), the process proceeds to S206, and when it is equal to or less than FFTi (MAX), the process proceeds to S207. Regarding the process of S205, there are a total of five vibration intensities FTTi obtained by the FFT process for each resonance frequency. Here, one of them is selected as appropriate. Since the frequency number i = 1 (FIG. 3) tends to be greatly influenced by noise components other than the knocking sound, for example, the frequency number i = 1 is adopted.

In S206, the count value MAX is set to m. That is, the count value MAX indicates the number of the FFT process in which the maximum vibration intensity is obtained in the detection period. For example, when MAX = 3, the vibration intensity FTTi (3) obtained by the third FFT processing is the maximum among the vibration intensity obtained from the start of the detection period to the present.
In S207, it is determined whether or not the count value m has reached a value obtained by subtracting the length Tgate of the analysis period from the predetermined value Nmax. When this value (= Nmax−Tgate) is reached, the process proceeds to S208, and when it has not reached, the process returns to S204, where the vibration intensity FFTi (m + 1) obtained by the next FFT process and FFTi (MAX) Make a comparison.

In S208, the intensity σFFTi for each integrated frequency is calculated. The calculation of σFFTi is performed by integrating each vibration intensity obtained by the FFT processing from the MAX times to the MAX + Tgate times for each resonance frequency.
In S209, it is determined whether the engine speed Ne is higher than a predetermined value Ne1, that is, whether the windows are overlapped during the FFT processing. When it is higher than Ne1, the process proceeds to S210, and when it is equal to or less than Ne1, the process proceeds to S211.

In S210, the area correction corresponding to the overlap of the windows by the following equations (2) and (3) is performed on the integrated frequency intensity σFFTi, and the obtained value is set to the integrated frequency intensity σFFTi again. In Equation (3), Nol indicates the time (= Nsmp−Nh) at which the windows overlap.
σFFTi = σFFTi × Nhos / (Tgate × Nsmp) (2)
Nhos = Tgate × Nsmp-Nol × (Tgate-1) (3)
Here, the concept of area correction in S210 will be described with reference to FIG. In the present embodiment, the windows are overlapped at the time of high rotation, and Nsmp is set to 64 and Nh is set to 16 as described above. Therefore, the time Nol during which the windows overlap is the difference between them, that is, 48. . Under such a setting, for example, a case is assumed where the intensity σFFTi for each integrated frequency is calculated by setting the length Tgate of the analysis period to 6. In this case, the six windows are set so as to be shifted by a length of ¼, and the reflection degree of the vibration intensity FFTi for each time with respect to the integrated frequency-specific intensity σFFTi and further to the frequency-specific intensity KDLi is different. Thus, the degree is relatively small between the first period indicated by A and the end period indicated by B in the figure. Equation (2) converts the integrated frequency-specific strength σFFTi into that when the windows do not overlap. As a result of the area correction by the equation (2), the respective vibration strengths FFTi are equally reflected in the frequency-specific strength KDLi regardless of the time zone.

  In S211, the integrated frequency-specific strength σFFTi is normalized with respect to the crank angle. In this embodiment, as this normalization, the integrated frequency-specific strength σFFTi is converted to ATDC 10 to 60 °, that is, per detection period by the following equations (4) and (5). In equation (4), the total number of data sampled for one knock determination is Nsmall.

σFFTi = σFFTi × {Nsmall−Nol × (Nmax−1)} / Nhos (4)
Nsmpall = Nmax × Nsmp (5)
In S212, knock determination is performed according to the flowchart shown in FIG. 6 based on the normalized σFFTi.

In the flowchart shown in FIG. 6, in S301, the determination result when the knock determination is performed for the cylinder j last time is cleared.
In S302, the frequency-specific strength KDLi is calculated. The calculation of KDLi is performed by reading the intensity σFFTi for each integrated frequency and dividing the read σFFTi by the engine speed Ne.

KDLi = σFFTi / Ne (6)
In S303, the background level BGL is calculated. In this embodiment, the background level BGL is calculated as the weighted average value of the frequency-specific intensity (hereinafter referred to as “average frequency-specific intensity”) KDavei according to the following equation (7). Note that the intensity by average frequency calculated in S303 at the time of the previous knock determination is set to KDLavein _-1 .

BGL = KDLavei = (KDLi + 15 × KDLavein _-1 ) / 16 (7)
In S304, the SN difference ΔKDLi is calculated. The SN difference ΔKDLi is the difference between the frequency-specific strength KDLi and the background level BGL, and ΔKDLi is calculated by subtracting the average frequency-specific strength KDlavei from the frequency-specific strength KDLi.

ΔKDLi = KDLi−KDLAvey (8)
In S305, it is determined whether or not the calculated SN difference ΔKDLi is equal to or smaller than a threshold value SLi for knock determination. The threshold value SLi is set for each resonance frequency according to the engine speed Ne. When all the frequency-specific intensities KDLi corresponding to the resonance frequency are less than or equal to SLi, the process proceeds to S306, and when at least one of the frequency-specific intensities KDLi is larger than SLi, a knock sound is detected. As a result, the process proceeds to S307.

In S306, it is determined that knocking has not occurred for the cylinder j.
In S307, it is determined that knocking has occurred in the cylinder j. When the ECU 22 determines that knocking has occurred, the ECU 22 performs the control described with respect to B11 in FIG. 2 to suppress the generated knocking.
Regarding the present embodiment, the in-cylinder pressure sensor 21 and the ECU 22 constitute a knock control device. That is, the in-cylinder pressure sensor 21 has a function as in-cylinder pressure detection means. Of the functions of the ECU 22, the function of S103 in the flowchart shown in FIG. 4 corresponds to the pressure storage means, and the function of S109 corresponds to the vibration intensity calculation means. The functions of S202 to 207 in the flowchart shown in FIG. 5 correspond to the period setting means, and the functions of S208 to 212 correspond to the knock determination means.

According to this embodiment, the following effects can be obtained.
First, the detection period (= ATDC 10 to 60 °) is divided into time zones by a plurality of windows, and the maximum vibration intensity in the detection period is calculated based on the vibration intensity FFTi calculated as a result of the FFT processing for each window. As a period starting from the time when the above is obtained, an analysis period for determining a substantial object of knock determination is set. For this reason, in the in-cylinder pressure waveform, a highly probable waveform portion including a loud knocking sound is selected as an analysis target, a window is set for such a waveform portion, and the frequency-specific strength KDLi is calculated. Can do. For example, when an analysis period is set as shown in FIG. 10, hatched windows (w2 to w4 for low rotation, w2 and w3 for high rotation) are set as the windows that fit in this analysis period. The As a result, in the calculated KDLi, it is possible to suppress the influence of noise components other than the knocking sound, so that the difference between the calculated KDLi and the background level BGL can be made large, and the occurrence of knocking can be easily performed. Can be detected.

  Regarding the first effect, in S207 of the flowchart shown in FIG. 5, the time when the maximum vibration strength is obtained among the vibration strengths obtained until Nmax-Tgate FFT processing is performed is the start of the analysis period. By doing so, it is possible to prevent the in-cylinder pressure Pcyl required for performing the FFT processing a predetermined number of times without failing to ensure that the analysis period is within the detection period.

  Secondly, in the FFT process, the windows are overlapped with a length corresponding to the engine speed Ne. For this reason, the substantial resolution of the FFT process under high rotation can be improved, and the determination accuracy required over the entire operation region can be realized. Here, the effect of improving the resolution can be made more remarkable by extending the overlap as the engine speed Ne is higher. On the other hand, at the time of low rotation, the overlap is shortened (including the case where the overlap is not performed), so that an unnecessary increase in calculation load can be avoided and both determination accuracy and calculation load can be achieved.

  Third, when the windows are set to overlap, the area for the overlap is corrected for the integrated frequency-specific strength σFFTi, and the result is averaged with respect to time by converting to the case where the windows do not overlap. It was decided. For this reason, in knock determination, it is not necessary to change the handling of the threshold value according to the presence or absence of overlap or the difference in length thereof, and the knock determination can be performed by centralized comparison with the threshold value.

  Fourth, at the time of knock determination, the crank angle is normalized by converting the integrated frequency-specific strength σFFTi into a predetermined crank angle range (= ATDC 10 to 60 °), that is, per detection period. In the present embodiment, the length of the analysis period is changed in accordance with the engine speed Ne (FIG. 8), and the calculated σFFTi is normalized with respect to the crank angle, so that the frequency-dependent strength KDLi is obtained by the change in the length. The variation which arises can be compensated and the fall of determination accuracy can be controlled.

  In the above description, FFT is used as the frequency conversion means for the in-cylinder pressure waveform. However, for example, wavelet conversion may be used instead of FFT.

Configuration of an engine including a knock control device according to an embodiment of the present invention Configuration of knock control device Resonance mode configuration and mode coefficient ρmn in draper equation Flow chart of vibration intensity calculation routine Knock determination routine flowchart Subroutine of knock determination processing in the same routine Detection start timing and detection end timing of in-cylinder pressure Pcyl Relationship between engine speed Ne and analysis period Area correction concept for window overlap Relationship between detection period and analysis period

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Engine, 11 ... Intake passage, 12 ... Throttle valve, 13 ... Air flow meter, 14 ... Intake valve, 15 ... Injector, 16 ... Spark plug, 17 ... Exhaust valve, 18 ... Exhaust passage, 19 ... Crank angle sensor, 20 ... Cooling water temperature sensor, 21 ... In-cylinder pressure sensor, 22 ... Control unit.

Claims (9)

In-cylinder pressure detecting means for detecting a vibration component of the in-cylinder pressure during combustion,
Pressure storage means for storing the pressure detected by the in-cylinder pressure detection means in a first period preset as a period starting from a predetermined crank angle position;
Based on the stored pressure, vibration intensity calculation means for calculating vibration intensity in a predetermined frequency band set to indicate the characteristics of knocking in time series,
A period setting means for setting a second period shorter than the first period based on the calculated vibration intensity;
An engine comprising: knock determining means for determining whether or not knocking has occurred in the engine based on at least one vibration intensity calculated by the vibration intensity calculating means during the set second period. Knock control device.   2. The engine knock according to claim 1, wherein the period setting unit sets the second period as a period starting from a time when the maximum value in the first period of the vibration intensity calculated by the vibration intensity calculating unit is obtained. Control device.   The engine knock control apparatus according to claim 1 or 2, wherein the period setting means sets the second period to end before the end of the first period.   The engine knock control according to any one of claims 1 to 3, wherein the vibration intensity calculation means calculates each vibration intensity corresponding to each of a plurality of overlapping periods with respect to time according to the engine speed. apparatus.   The engine knock control device according to claim 4, wherein the vibration intensity calculation means extends the aura lap during a period for calculating the vibration intensity as the engine speed is higher.   When the periods during which the vibration intensity is calculated overlap, the knock determination means averages the vibration intensity calculated by the vibration intensity calculation means with respect to time, and determines whether knocking has occurred based on the average vibration intensity. The engine knock control device according to claim 4 or 5 for determination.   The engine according to any one of claims 1 to 6, wherein the knock determination means converts the vibration intensity calculated by the vibration intensity calculation means into a value per predetermined crank angle when determining whether or not knocking has occurred. Knock control device.   The engine knock control apparatus according to any one of claims 1 to 7, further comprising means for changing an ignition timing in accordance with a determination result of the knock determination means. In a first period set in advance as a period starting from a predetermined crank angle position, the combustion pressure including vibration components is detected, and the characteristic of knocking is set based on the detected combustion pressure. Calculate the vibration intensity of the selected frequency band in chronological order,
Based on the calculated vibration intensity, set a second period shorter than the first period and included in the first period,
Based on at least one vibration intensity calculated as the vibration intensity in the frequency band for the set second period, it is determined whether knocking has occurred in the engine,
An engine knock control apparatus that performs control for suppressing knocking when it is determined that knocking has occurred.

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