Patent Publication Number: US-2009217738-A1

Title: Knock detection device for internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on Japanese Patent Application No. 2008-50264 filed on Feb. 29, 2008, the disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a knock detection device for an internal combustion engine. The knock detection device detects a knock on the basis of a time-varying pattern of vibration intensity extracted from an output signal of a knock signal output device. 
     BACKGROUND OF THE INVENTION 
     As described in JP-2005-188297A, when a knock is caused, a phenomenon called “a low frequency shift” is caused. In the low frequency shift, a peak frequency of a vibration component specific to the knock gradually shifts to a lower frequency side. When a peak frequency of vibration component of one knock frequency range extracted from the output signal of the knock sensor gradually shifts to a lower frequency side, it is determined that a knock is caused. 
     An internal combustion engine is provided with various systems such as a variable valve timing controller and a super-charger in order to improve an output, a fuel economy and an environmental performance. A direct injection engine varies fuel injection timing according to a combustion mode. Thus, many kinds of noises tend to superimpose on the signal of the knock sensor in a knock determination range. However, in the knock detection apparatus described in JP-2005-188297A, it is only determined whether a vibration component of one knock frequency range shifts to a lower frequency side in time sequence. Thus, as shown in  FIG. 4 , when a plurality of noises are superimposed on the signal of the knock sensor in time sequence in one knock determination range, there is a possibility of making an erroneous determination that one continuous vibration component will shift apparently to a lower frequency side. Therefore, when it is only determined whether the vibration component of one frequency range shifts to a lower frequency side, there is a possibility of making an erroneous determination that a knock is caused. 
     SUMMARY OF THE INVENTION 
     The present invention is made in view of the above matters, and it is an object of the present invention to provide a knock detection device for an internal combustion engine, which can avoid an erroneous knock determination due to noises being superimposed on the output signal of a knock signal output device, even if the noises increase. Hence, knock determination accuracy is enhanced. 
     According to the present invention, a knock detection device includes: a knock signal output means for outputting an output signal of which waveform is varied according to a knock caused while the internal combustion engine is operated; a vibration intensity extraction means for extracting time-varying patterns of vibration intensity in multiple frequency ranges from the output signal of the knock signal output means; and a knock determination means for executing a knock determination based on at least two of a plurality of vectors indicating directions along which vibration intensities in a plurality of frequency ranges temporally vary. 
     When knock is caused, not only a knock vibration component of a basic frequency of the knock (first-order resonance frequency which is determined by the diameter of the bore of a cylinder and which is about, for example, 7.5 kHz), but also knock vibration components develop at the same time in second-order and higher-order resonance frequency ranges. A phenomenon that plural noises are continuously caused like a low frequency shift is not a phenomenon that develops in plural frequency ranges at the same time but a phenomenon that develops only in a portion of frequency ranges. 
     According to the present invention, the time-varying patterns of vibration intensity of multiple frequency ranges are extracted from the output signal of the knock signal output means, and a knock determination is executed based on at least two of vectors indicating directions along which vibration intensities in a plurality of frequency ranges temporally vary. Thus, even if a low frequency shift that cannot be distinguished from the knock is developed in any one of frequency range due to a noise being superimposed on the output signal of the knock signal output means, it is possible to prevent making an erroneous determination that the low frequency shift developed by the noise is the knock and hence to increase a knock determination accuracy. 
     The time-varying patterns of vibration intensity in multiple frequency ranges can be extracted by means of a plurality of band pass filters. Alternatively, a time-frequency analysis of the output signal of the knock signal output means may be performed in order to extract the time-varying patterns of vibration intensity in multiple frequency ranges. The time-frequency analysis includes a short-time Fourier transform (STFT), a wavelet transform, a Wigner distribution. By performing the time-frequency analysis, the data of frequency, time, and vibration intensity can be extracted at the same time from the output signal of the knock signal output means, and the time-varying pattern of vibration intensity of multiple frequency ranges can be produced. 
     The knock determination may be executed based on whether directions of any two or more of the vectors are within a predetermined range. If the directions of at least two of vectors agree with a direction of the low frequency shift, it can be determined that a knock is caused. 
     Alternatively, the knock determination means relates lengths of vectors to lengths of the time-varying patterns of vibration intensity in multiple frequency ranges, and the knock determination may be executed based on whether a ratio of lengths of any two of vectors is within a predetermined range. 
     Alternatively, a knock determination may be executed based on vibration intensities (area) of at least two of the timing-varying patterns of vibration intensities in multiple frequency ranges. 
     The time-varying patterns of vibration intensity of multiple frequency ranges can be extracted by a time-frequency analysis of the output signal of the knock signal output means. 
     Alternatively, a knock determination may be executed based on whether a ratio between vibration intensities (area) of any two of the time-varying patterns of vibration intensity in multiple frequency ranges is within a predetermined range. 
     Generally, the condition in which the knock is easily caused is changed according to an engine speed and/or an engine load. The predetermined range can be varied according to the engine speed and/or the engine load. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages of the present invention will become more apparent from the following description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which: 
         FIG. 1  is a schematic view of an engine control system according to a first embodiment of the present invention; 
         FIG. 2  is a block diagram showing a circuit for processing the output signal of a knock sensor to make a knock determination; 
         FIG. 3  is a graph schematically showing time-varying patterns of vibration intensity of multiple frequency ranges extracted from output signals of a knock sensor; 
         FIG. 4  is a graph showing an example in which when the time-varying pattern of vibration intensity is extracted from only one frequency range, an erroneous determination that knock is caused is made due to noises being superimposed on the output signal of the knock sensor; 
         FIG. 5  is a flow chart showing a processing of a knock determination routine according to a first embodiment; and 
         FIG. 6  is a flow chart showing a processing of a knock determination routine according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be described hereinafter. 
     First Embodiment  
     Referring to  FIGS. 1 to 5 , a first embodiment will be described hereinafter. Referring to  FIG. 1 , an engine control system is explained. An air cleaner  13  is arranged upstream of an intake pipe  12  of an internal combustion engine  11 . An airflow meter  14  detecting an intake air flow rate is provided downstream of the air cleaner  13 . A throttle valve  15  driven by a motor  10  and a throttle position sensor  16  detecting a throttle position are provided downstream of the air flow meter  14 . 
     A surge tank  17  including an intake air pressure sensor  18  is provided downstream of the throttle valve  15 . The intake air pressure sensor  18  detects intake air pressure An intake manifold  20  is connected to the surge tank  17 . A fuel injector  20  is mounted on each cylinder for injecting fuel into an interior of the cylinder respectively. A spark plug  21  is mounted on a cylinder head of the engine  11  corresponding to each cylinder. Each spark plug  21  receives high voltage generated by an ignition device  25  to ignite air-fuel mixture in each cylinder. 
     The engine  11  is provided with an intake valve timing controller  31  which adjusts a valve timing of the intake valve  29 , and an exhaust valve timing controller  32  which adjusts valve timing of an exhaust valve  30 . 
     An exhaust pipe  22  of the engine  11  is provided with a three-way catalyst  23  purifying CO, HC, NOx and the like in the exhaust gas. An exhaust gas sensor  24  detecting air-fuel ratio or rich/lean of the exhaust gas is disposed upstream of the three-way catalyst  25 . A crank angle sensor  26  is installed on a cylinder block of the engine  11  to output crank angle pulses when a crank shaft rotates a predetermined angle. Based on these crank angle pulses of the crank angle sensor  26 , a crank angle and an engine speed are detected. 
     The cylinder block of the engine  11  is mounted with a knock sensor  28  for detecting knock vibration, and the output signal of the knock sensor  28  is digitally processed by a knock determination circuit  33  to perform a knock determination. The knock sensor  28  corresponds to a knock signal output means. The knock determination result made by the knock determination circuit  33  is inputted to an electronic control unit  34 , which is referred to as ECU  34 , hereinafter. The ECU  34  includes a microcomputer which executes an engine control program stored in a Read Only Memory (ROM) to control a fuel injection quantity of the fuel injector  20 , an ignition timing of the spark plug  21 , and a valve timing of the variable valve timing controllers  31 ,  32 . The ECU  34  repeatedly performs a following knock control so that an ignition timing comes close to a knock limit. That is, when the knock determination circuit  33  detects no knock, the ignition timing is advanced, whereas when the knock determination circuit  33  detects a knock, the ignition timing is retarded. 
     As shown in  FIG. 3 , when knock is caused, not only a knock vibration component of the basic frequency of the knock (first-order resonance frequency determined by the diameter of the bore of the cylinder) but also knock vibration components of the second-order or more, that is, higher-order resonance frequency ranges develop at the same time. When the knock is caused, the low frequency shift occurs. That is, the vibration components of these multiple frequency ranges gradually shift to a lower frequency side. As shown in  FIG. 4 , when a plurality of noises are superimposed on the output signal of the knock sensor  28  in time sequence within one knock determination range, there is a possibility of making an erroneous determination that one continuous vibration component will apparently causes a low frequency shift. Thus, when it is only determined whether a vibration component of one frequency range causes a low frequency shift, there is a possibility of making an erroneous knock determination. 
     The feature of the knock includes the following four features. 
     (1) A vibration intensity increases rapidly. 
     (2) Knock attenuates logarithmically (vibration continues). 
     (3) A vibration intensity develops in multiple frequency ranges. 
     (4) A low frequency shift develops. 
     According to the first embodiment, time-varying patterns of vibration intensity in multiple frequency ranges are extracted from an output signal of the knock sensor  28 . Then, a knock determination is executed based on whether directions of any two or more of multiple vectors are within a predetermined range. Alternatively, a knock determination is executed based on whether a ratio of length of any two or more of the vectors is within a predetermined range. The vectors indicate variation directions of the vibration intensity in multiple frequency ranges. The ratio of vector length is a ratio of length in a direction of the low frequency shift. 
     In the present first embodiment, a time-frequency analysis is used to extract the time-varying patterns of vibration intensity in multiple frequency ranges from the output signals of the knock sensor  28 . A short-time Fourier transform (STFT), a wavelet transform, a Wigner distribution, or the like is used as the time-frequency analysis. 
     The processing of the time-frequency analysis is performed by a time-frequency analysis part  42  in the knock determination circuit  33 . The time-frequency analysis part  42  corresponds to a vibration intensity extraction means. The output signal of the knock sensor  28  is converted to a digital value by an A/D conversion part  41 . The converted signal is processed by the time-frequency analysis part  42 . When a knock is caused, as shown in  FIG. 3 , time-varying patterns are extracted in the multiple frequency ranges. The frequency ranges in which the time-varying pattern of vibration intensity is extracted include a range of a basic frequency, which is the lowest frequency of the frequencies of the knock vibrations, and the ranges of the second or higher-order resonance frequencies of the knock vibrations. The basic frequency is the first-order resonance frequency determined by the diameter of the bore of the cylinder 
     A plurality of vectors A 1 -A 4  indicating variation directions of vibration intensity in multiple frequency ranges are computed by a knock determination part  43  on the basis of the analysis result of the time-frequency analysis part  42 . Then, a knock determination is made based on whether the directions of the vectors A 1 -A 4  or the ratio between the lengths of the vectors A 1 -A 4  are within the predetermined ranges. The vector length corresponds to a length of the time-varying pattern of vibration intensity in a direction of the low frequency direction. 
     Specifically, an edge extraction technique of image processing is applied to the result of the time-frequency analysis shown in  FIG. 3  in order to extract the contours (edges) of the time-varying patterns of vibration intensity of multiple frequency ranges. For example, in  FIG. 3 , in a case that a time axis (crank angle axis) direction is an x direction, a frequency axis direction is a y direction, and a pixel value at arbitrary coordinates (x, y) is G(x, y), the gradient of density at the coordinates (Δx, Δy) is expressed by the following equations. 
       Δ x ( x, y )= G ( x− 1,  y )− G ( x, y ) 
       Δ y ( x, y )= G ( x, y− 1)− G ( x, y ) 
     An edge intensity Vn(x, y) at the arbitrary coordinates (x, y) is expressed by the following equation. 
         Vn ( x, y )=√{square root over (Δ x ( x, y ) 2   +Δy ( x, y ) 2 )}{square root over (Δ x ( x, y ) 2   +Δy ( x, y ) 2 )}  [Equation 1] 
     An edge direction θn(x, y) at the arbitrary coordinates (x, y) is expressed by the following equation. 
     
       
         
           
             
               
                 
                   
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     The edge direction θn(x, y) points from a dark side of a change in the density to a light side. A portion where the gradient of density (Δx, Δy) changes by a specified value or more may be determined to be a contour. Alternatively, a portion where a density change quantity in the adjacent regions changes by a specified value or more may be determined to be a contour. Further, a contour (edge) extraction method may be changed according to an engine speed and/or an engine load. 
     After the processing of extracting the contours (edges) of the time-varying patterns of vibration intensity in the multiple frequency ranges is finished, the knock determination part  43  approximates the vectors A 1 -A 4  by the contour of the time-varying patterns of vibration intensity according to the least-squares method. Thereby, the directions of the vector A 1 -A 4  are mostly in agreement with the directions of the low frequency shift of the vibration intensity in each frequency area. 
     The knock determination is executed based on whether the directions of any two or more of the vectors A 1 -A 4  within the predetermined range. Alternatively, the knock determination is executed based on whether a ratio of length of any two of the vectors A 1 -A 4  is within the predetermined range. The ratio of vector length is expressed by |A 1 |/|A 3 |, |A 1 |/|A 2 |, |A 1 |/|A 4 |, |A 2 |/|A 4 |, or |A 2 |/|A 3 |, for example. It should be noted that the predetermined range includes dispersion due to a knock being caused. 
     The information of the determination result of the knock determination part  43  is sent to the ECU  34 . The ECU  34  repeatedly performs a knock control in which the ignition timing is advanced when no knock is detected and the ignition timing is retarded when a knock is detected, whereby the ignition timing comes close to a knock limit. 
     The above-mentioned knock determination processing is performed by the knock determination circuit  33  according to a knock determination routine shown in  FIG. 5 . The knock determination routine shown in  FIG. 5  is performed for each one ignition of each cylinder. In step  101 , the output signal of the knock sensor  28  is converted by the A/D conversion part  41  to a digital signal in a specified knock determination range. In step  102 , the time-frequency analysis (STFT, wavelet transform, Wigner distribution, or the like) is performed to extract the data of frequency, time, and vibration intensity at the same time from the output signal of the knock sensor  28 , thereby extracting the time-varying patterns of vibration intensity in the multiple frequency ranges. Thereafter, the procedure proceeds to step  103  in which a contour extraction processing is performed to compute the edge direction θn(x, y) and the edge intensity Vn(x, y) according to the equation (1) and the equation (2), whereby contours of the time-varying patterns of vibration intensity in the multiple frequency ranges are extracted. 
     Then, the procedure proceeds to step  104  in which the vectors A 1 -A 4  are approximated by the contour of the time-varying pattern of vibration intensity in each frequency range according to the least-squares method. Then, the procedure proceeds to step  105  in which the knock determination is executed based on whether the directions of two or more of vectors A 1 -A 4  are within the predetermined range. Alternatively, the knock determination is executed based on whether a ratio of length of any two of vectors A 1 -A 4  is within the predetermined range. When the answer is Yes in step  105 , the procedure proceeds to step  106  in which the computer determines that a knock is caused. When the answer is No in step  105 , the procedure proceeds to step  107  in which the computer determines that no knock is caused. With this manner, even if a low frequency shift that cannot be distinguished from the knock in any one of the frequency ranges is developed due to the noises being superimposed on the output signal of the knock sensor  28 , it is possible to prevent making an erroneous determination that the low frequency shift developed by the noises is the knock. Thus, the knock determination accuracy is enhanced. 
     As for the predetermined range (a determination threshold), a constant value (fixed value) may be used which is previously set in an adjustment process on the basis of the intensity and the frequency that can be allowed from the sense of hearing of the worker. However, the condition in which the knock is easily caused varies according to engine speed, engine load, and the like, so that the predetermined range may be set according to the engine speed and/or the engine load. With this, it is possible to determine whether a knock is caused under the knock determination condition suitable for the engine speed and/or the engine load. 
     The predetermined range may be corrected according to a knock detection frequency. Under the operating condition in which the knock detection frequency is low, the predetermined range is set narrow to make it difficult to detect the knock. The ignition timing is advanced to improve the output and the fuel economy. Under the operating condition in which the knock detection frequency is high, the predetermined range is set wide to make it easy to detect a knock. The ignition timing is retarded to restrict the knock within an allowance in terms of the sense of hearing. 
     Second Embodiment  
     According to the second embodiment shown in  FIG. 6 , a knock determination is executed based on whether a ratio of vibration intensity (area) between any two of the time-varying patterns is within a predetermined range. The other configurations are the same as those of the first embodiment. 
     The knock determination routine shown in  FIG. 6  is performed for each one ignition of each cylinder. In step  201 , the output signal of the knock sensor  28  is converted by the A/D conversion part  41  to a digital signal. In step  202 , a time-frequency analysis is executed to extract data of frequency, time, and vibration intensity at the same time from the output signal of the knock sensor  28 . Then, the time-varying patterns of vibration intensity in multiple frequency ranges are extracted. The procedure proceeds to step  203  in which contours of the time-varying patterns of vibration intensity in multiple frequency ranges are extracted. 
     Then, the procedure proceeds to step  204  in which the vibration intensities (areas) of any two of time-varying patterns of vibration intensity in multiple ranges are computed and a ratio between two vibration intensities is computed. The procedure proceeds to step  205  in which the computer determines whether the ratio between two vibration intensities is within the predetermined range. When the answer is Yes in step  205 , the procedure proceeds to step  206  in which the computer determines that a knock is caused. When the answer is No, the procedure proceeds to step  207  in which the computer determines that no knock is caused. With this manner, even if a low frequency shift that cannot be distinguished from the knock in any one of the frequency ranges is developed due the noises being superimposed on the output signal of the knock sensor  28 , it is possible to prevent making an erroneous determination that the low frequency shift developed by the noises is the knock. Thus, the knock determination accuracy is enhanced. 
     As for the predetermined range (a determination threshold), a constant value (fixed value) may be used which is previously set in an adjustment process on the basis of the intensity and the frequency that can be allowed from the sense of hearing of the worker. However, the condition in which the knock is easily caused varies according to engine speed, engine load, and the like, so that the predetermined range may be set according to the engine speed and/or the engine load. With this, it is possible to determine whether a knock is caused under the knock determination condition suitable for the engine speed and/or the engine load. 
     The predetermined range may be corrected according to a knock detection frequency. Under the operating condition in which the knock detection frequency is low, the predetermined range is set narrow to make it difficult to detect the knock. The ignition timing is advanced to improve the output and the fuel economy. Under the operating condition in which the knock detection frequency is high, the predetermined range is set wide to make it easy to detect a knock. The ignition timing is retarded to restrict the knock within an allowance in terms of the sense of hearing. 
     In the above embodiments, the time-frequency analysis is used to extract the time-varying pattern of vibration intensity of the multiple frequency ranges from the output signal of the knock sensor  28 . Alternatively, the time-varying pattern of vibration intensity in the multiple frequency ranges may be extracted by means of multiple band pass filters corresponding to the multiple frequency ranges. 
     In the above embodiments, the knock sensor  28  is used as the knock signal output means of which output signal waveform is varied according to the knock caused during the engine operation. Alternatively, a cylinder pressure sensor for detecting a cylinder pressure or an ion current detection means for detecting ions produced by the combustion of the air-fuel mixture in the cylinder through the ignition plug  21  or the like may be used as the knock signal output means. 
     The present invention is not limited to a direct injection engine shown in  FIG. 1  but can be applied also to an intake port injection engine and a dual injection engine having fuel injectors mounted in both of the intake port and the cylinder. Further, the present invention can be applied to an engine not mounted with a variable valve unit such as a variable valve timing controller. The present invention can be variously modified and put into practice within a range not departing from the spirit and scope of the present invention.