JP5386399B2 - Internal combustion engine knock detection device - Google Patents

Description

  The present invention relates to a knocking detection device for an internal combustion engine.

  A technique is known in which when the occurrence of knocking in an internal combustion engine is detected, ignition timing correction or air-fuel ratio correction is performed to suppress the occurrence of knocking. In connection with the technology for detecting knocking, the vibration of the internal combustion engine is detected, and the maximum vibration pressure detected by the combustion pressure sensor when the vibration intensity at the frequency specific to knocking exceeds a predetermined threshold value. It is known that when a value exceeds a certain value, it is determined that true knocking that is not pseudo knocking has occurred (see Patent Document 1).

JP 2002-364446 A

  The threshold for determining the occurrence of knocking is determined based on the magnitude of the audible knock sound. Even if the audible knock noise is the same, the combustion pressure depends on the rotational speed of the internal combustion engine. The amplitudes of vibrations are different, and the combustion pressure oscillations tend to be significantly larger when the internal combustion engine is operating at high speed than when the internal combustion engine is operating at low speed. Frequent occurrence of large combustion pressure oscillations can overload the internal combustion engine and reduce the reliability of the internal combustion engine. Therefore, it is desirable to perform control to suppress knocking in such a state. However, in the conventional technique, there is a possibility that such a state cannot be detected as occurrence of knocking.

  The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide a knocking detection device capable of accurately detecting knocking of an internal combustion engine.

In order to achieve the above object, a knock detection device for an internal combustion engine according to the present invention comprises:
Vibration detecting means for detecting vibration of a cylinder block of the internal combustion engine;
Combustion pressure detecting means for detecting the combustion pressure of the internal combustion engine;
A first determination is made as to whether or not knocking has occurred based on a comparison between a predetermined first threshold and the intensity of vibration in a frequency range unique to knocking or the physical quantity correlated therewith among the vibrations detected by the vibration detection means. 1 determination means;
Second determination means for determining whether or not the intensity of the vibration in the frequency range specific to knocking among vibrations of the combustion pressure detected by the combustion pressure detection means is greater than a predetermined second threshold;
The determination by the second determination means is performed a plurality of times, and the ratio of the number of times that the vibration intensity of the combustion pressure is determined to be greater than the second threshold among the plurality of times is greater than a predetermined third threshold. Correcting means for correcting the first threshold value in a direction in which it is easy to determine that knocking has occurred by the first determining means;
It is characterized by having.

The first threshold value is determined based on the volume of the knock sound on hearing. Each of the second threshold value and the third threshold value is determined so that it can be determined whether or not there is a possibility that the internal combustion engine will be overloaded and the reliability of the internal combustion engine may be reduced. According to the knocking detection device having the above-described configuration, when it is detected that the combustion pressure vibration having the intensity exceeding the second threshold is generated at a high frequency exceeding the third threshold, the first determination is made. It becomes easy to determine that knocking has occurred by the means.

  Therefore, it is possible to accurately detect a state in which combustion pressure vibration with such a magnitude that an excessive load may be applied to the internal combustion engine occurs as occurrence of knocking. If the knocking detection device according to the present invention is used for knocking detection in a system that performs ignition timing control or air-fuel ratio control for suppressing knocking according to knocking detection, an excessive burden may be placed on the internal combustion engine. Since it is possible to prevent the combustion pressure vibration with such a high frequency from continuing, it is possible to suppress a decrease in the reliability of the internal combustion engine.

  Even when the audible knock noise is the same, the intensity of combustion pressure vibration tends to increase as the rotational speed of the internal combustion engine increases. Therefore, when the internal combustion engine is in an operating state at a high rotational speed, it is likely to be in a state where frequent combustion pressure vibrations that may cause an excessive burden on the internal combustion engine occur.

  Therefore, in the present invention, the correction means may execute the correction process when the rotational speed of the internal combustion engine is higher than a predetermined fourth threshold value.

  This makes it easier to detect that knocking has occurred in a high-speed operation state in which a combustion pressure vibration with a strength that may cause an excessive load on the internal combustion engine is likely to occur.

In the present invention, the internal combustion engine is a spark ignition internal combustion engine,
Control means for performing at least one of control for retarding the ignition timing of the internal combustion engine and control for making the air-fuel ratio of the internal combustion engine rich when the first determination means determines that knocking has occurred; You may make it have.

  By retarding the ignition timing or making the air-fuel ratio rich, it is possible to achieve a combustion state in which intense combustion pressure oscillations that place an excessive burden on the internal combustion engine do not occur frequently. Can be suppressed.

In the present invention, the first determination means has a predetermined first threshold value that has a predetermined degree of variation in the detected value in a predetermined period of the intensity of the vibration in the frequency range unique to knocking among the vibrations detected by the vibration detection means. If it is larger, it is determined that knocking has occurred,
The correction process by the correction unit may be correction for reducing the first threshold value.

  The degree of variation of the detected value in the predetermined period can be obtained by calculating a standard deviation, for example.

  The knock detection device for an internal combustion engine according to the present invention can detect knocking of the internal combustion engine with high accuracy.

It is a figure which shows schematic structure of the knocking detection apparatus of the internal combustion engine of an Example. It is the figure which plotted the output of the vibration sensor and the combustion pressure sensor over several cycles in each of the case where an engine is a low speed and the case of a high speed. It is a flowchart showing the process which correct | amends the 1st threshold value for determining knocking generation which concerns on an Example according to the generation | occurrence | production state of combustion pressure vibration. It is a figure which shows the example of the driving | operation area | region where the process which correct | amends the 1st threshold value for determining knocking generation which concerns on an Example according to the generation | occurrence | production state of combustion pressure vibration is performed. It is a figure which shows the example of the relationship between the ratio of the frequency | count that the amplitude of the natural vibration of a combustion pressure vibration exceeded the 2nd threshold value, and the occurrence of the failure of a piston.

  Hereinafter, embodiments of the present invention will be described in detail. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a diagram showing a schematic configuration of a spark ignition type gasoline engine which is an embodiment of a knocking detection device for an internal combustion engine of the present invention. In FIG. 1, the engine 3 has a cylinder block 12 and a cylinder head 11, and a cylinder 7 in which a piston 14 is slidably inserted is formed in the cylinder block 12. The cylinder head 11 is formed with an intake port 13 that connects an unillustrated intake passage and the cylinder 7, and an exhaust port 5 that connects an unillustrated exhaust passage and the cylinder 7. The intake port 13 is opened and closed by an intake valve 8. The exhaust port 5 is opened and closed by an exhaust valve 9.

  The cylinder head 11 is provided with a spark plug 10 for igniting the air-fuel mixture in the cylinder 7. An opening 20 is provided in the inner wall surface 6 of the cylinder 7, and a pressure introduction path 4 provided in the cylinder head 11 is connected to the opening 20. The pressure introduction path 4 guides the pressure in the cylinder 7 to the combustion pressure sensor 2 (combustion pressure detecting means), and the combustion pressure sensor 2 can detect the pressure in the cylinder 7.

  Returning to FIG. 1, the cylinder block 12 of the engine 3 is provided with a vibration sensor 1 (vibration detecting means) that detects vibration of the cylinder block 12. Further, a rotation speed sensor 16 that detects the rotation speed of the engine 3 and an air flow meter 17 that detects the intake air amount are provided. Detection values by the vibration sensor 1, the combustion pressure sensor 2, the rotation speed sensor 16, and the air flow meter 17 are input to the ECU 15.

  The ECU 15 is a computer that controls the operation of the engine 3 and has a known configuration such as a CPU, a ROM, a RAM, a D / A converter, and an A / D converter. The ECU 15 detects the operating state of the engine 3 based on the detection values input from the respective sensors, calculates the ignition timing and the fuel injection amount according to the detected operating state, and based on the ignition plug 10 and not shown Controls fuel injection valves and throttle valves.

  In this embodiment, the ECU 15 detects the occurrence of knocking based on the detection value obtained by the vibration sensor 1. That is, the vibration of the cylinder block 12 in a predetermined crank angle range (for example, ATDC 0 to 90 ° CA, ATDC 10 to 30 ° CA, etc.) in which knocking may occur by the vibration sensor 1 is detected. Among them, the vibration intensity in the frequency range specific to knocking generated in the engine 3 is acquired.

The frequency range specific to knocking depends on the design of the engine 3. When knocking occurs, a peak appears in the range of approximately 6 to 9 kHz. Further, a plurality of peaks appear due to the occurrence of knocking in a higher frequency range. The ECU 15 determines that the index value indicating the degree of variation in the intensity Y of the vibration in the frequency range specific to knocking (referred to as natural vibration) among the vibrations of the cylinder block 12 detected by the vibration sensor 1 is Y1 (first threshold value). If it is larger than that, it is determined that knocking has occurred. The ECU 15 that determines the occurrence of knocking as such functions as the first determination means in the present invention. Note that the standard deviation of the intensity Y over a predetermined period may be used as an index value representing the degree of variation in the natural vibration intensity Y.

  The first threshold value Y1 is based on the upper limit value of the natural vibration intensity of the cylinder block 12 when knocking with a level of knocking sound that is permissible for the occupant of the vehicle equipped with the engine 3 occurs in the adaptation process. Determine.

  When the index indicating the variation degree of the natural vibration strength Y of the cylinder block 12 detected by the vibration sensor 1 exceeds the first threshold Y1, it is determined that knocking has occurred, and knocking is suppressed (knocking of knocking). (Reducing the strength) Control. In the present embodiment, at least one of control for retarding the ignition timing by the spark plug 10 and control for making the air-fuel ratio rich is performed as control for suppressing knocking. The ECU 15 that performs this control functions as the control means in the present invention.

  For example, when performing control to retard the ignition timing, after delaying the ignition timing by a certain amount in response to detection of the occurrence of knocking, the angle is gradually advanced toward the MBT, so that the permissible level for auditory perception is increased. It is possible to control the ignition timing so that the maximum output can be obtained within a range in which excessive knock noise does not occur.

  As described above, the detection of knocking and the control for suppressing knocking are performed based on the level of audible knock sound. Even if the level of audible knock sound is the same, the intensity (amplitude) of combustion pressure vibration associated with knocking is detected. ) Was found to vary depending on the operating state of the engine 3. FIG. 2 shows a vibration sensor 1 when the knocking sound due to audibility is the same when the engine 3 has a low rotation speed (rotation speed NE = 2000 rpm) and when the engine 3 has a high rotation speed (rotation speed NE = 6000 rpm). FIG. 5 is a diagram in which the output of the combustion pressure sensor 2 is plotted over a plurality of cycles.

  The horizontal axis in FIG. 2 corresponds to the natural vibration amplitude of the cylinder block 12 detected by the vibration sensor 1. The vertical axis in FIG. 2 represents the amplitude of the vibration of the combustion pressure detected by the combustion pressure sensor 2 (referred to as natural vibration) at a frequency unique to knocking.

  As shown in FIG. 2, when the engine 3 has a high engine speed, the intensity of combustion pressure vibration varies greatly, and the engine 3 is significantly larger than the engine having a low engine speed even when the knock level is the same. It can be seen that strong combustion pressure oscillations may occur.

  In other words, even if the volume of the knocking sound is the same, when the engine 3 has a high engine speed, combustion pressure vibrations can be stronger than when the engine 3 has a low engine speed. Even when the occurrence of knocking is not detected, there may be a case where strong combustion pressure oscillation is applied that places an excessive burden on the engine. If strong combustion pressure vibration that causes an excessive load on the engine frequently occurs, the durability and reliability of the engine 3 may be reduced.

  Therefore, in the system of the present embodiment, the engine 3 has an excessive operating state that belongs to the operating region in which the rotational speed NE of the engine 3 is larger than the predetermined threshold value NE1 and the load factor KL of the engine 3 is larger than the predetermined threshold value KL1. It is defined as an operating state in which there is a high possibility that a strong combustion pressure vibration that causes a burden is generated, and when the operating state of the engine 3 belongs to this operating region, a strong combustion pressure that actually applies an excessive load to the engine 3 When it is detected that vibrations are frequently occurring, the correction process for correcting the above-described first threshold Y1 to a value Y1 ′ smaller than Y1 is performed.

In order to determine whether or not strong combustion pressure vibration that causes an excessive load on the engine 3 frequently occurs, for example, when the engine 3 is in the operating state of the high rotation and high load, for example, over a plurality of cycles (for example, 200 cycles), it is determined whether or not the amplitude X of the natural vibration of the combustion pressure vibration detected by the combustion pressure sensor 2 is greater than a predetermined second threshold value X1, and the amplitude X is the second in the determination over the plurality of cycles. The number of times determined to be greater than the threshold value X1 is integrated.

  Then, when the ratio C of the number of times that the detected amplitude X is determined to be greater than the second threshold value X1 is greater than the predetermined third threshold value C1, a strong combustion pressure oscillation that causes an excessive load on the engine 3 Is determined to occur frequently.

  By correcting the first threshold Y1 used for determining the occurrence of knocking to a smaller value Y1 ', it is easy to determine that knocking has occurred. As a result, control for suppressing (weakening) knocking such as retarding of the ignition timing is easily performed, so that strong combustion pressure vibration that causes an excessive burden on the engine 3 in a high-rotation and high-load operation state. Frequent occurrence can be suppressed, and deterioration of the durability and reliability of the engine 3 can be suppressed.

  FIG. 3 is a flowchart showing the process of correcting the first threshold described above. This flowchart is executed at predetermined intervals by the ECU 15 during operation of the engine 3. The ECU 15 that executes the processing of this flowchart functions as a second determination unit and a correction unit in the present invention.

  When the processing of this flowchart is started, the ECU 15 first acquires the operating state (the rotational speed NE and the load factor KL) of the engine 3 in step 100. The rotational speed NE is calculated based on the detection value input from the rotational speed sensor 16. The load factor KL is calculated based on the detection value input from the air flow meter 17. In the following step 101, the ECU 15 determines whether the acquired rotational speed NE is greater than the threshold value NE1 and whether the acquired load factor KL is greater than the threshold value KL1.

  If the rotational speed NE is equal to or less than the threshold value NE1 or the load factor KL is equal to or less than the threshold value KL1, the ECU 15 once exits the processing of this flowchart, and otherwise proceeds to step 102. In step 102, the amplitude X of the natural vibration of the combustion pressure vibration is detected by the combustion pressure sensor 2, and in step 103, it is determined whether or not the detected amplitude X is larger than the second threshold value X1.

  When the detected amplitude X is larger than the second threshold value X1, the ECU 15 proceeds to step 104 and calculates the integrated value of the number of times that the amplitude X was larger than the second threshold value X1 in the determination result of the last 200 cycles stored in the RAM. In addition to counting up, a ratio C that is a determination result that the amplitude X is greater than the second threshold value X1 in the latest 200 determinations is calculated. Then, in the following step 105, it is determined whether or not the calculated ratio C is larger than the third threshold C1. The total number of cycles for calculating the ratio C is not limited to 200.

  When the calculated ratio C is larger than the third threshold C1, the ECU 15 proceeds to step 106 and corrects the first threshold Y1 used when determining the occurrence of knocking in the high rotation / high load region to a value Y1 ′ smaller than Y1. To do. In the operation region other than the high rotation / high load region, the first threshold value used for determining the occurrence of knocking is not Y1 'but Y1.

When the detected amplitude X is less than or equal to the second threshold value X1 in step 103 and when the calculated ratio C is less than or equal to the third threshold value C1 in step 105, the ECU 15 once exits the process of this flowchart. When the detected amplitude X is equal to or smaller than the second threshold value X1 in step 103, the most recent 200 cycle determination result does not count up the number of times that the amplitude X is greater than the second threshold value X1, and The ratio C of the number of times that the amplitude X was determined to be larger than the second threshold value X1 among the 200 determinations may be calculated, and the processing after Step 105 may be performed.

  In this case, the calculated ratio C is smaller than the case where the affirmative determination is made in step 103, but the ratio for the last 200 times is still larger than the third threshold C1 (step 105). In the case of an affirmative determination), a decrease correction of the first threshold value Y1 is performed. When the number of times that the amplitude X is equal to or smaller than the second threshold value X1 increases to some extent and the ratio C decreases and becomes smaller than or equal to the third threshold value C1, a negative determination is made in step 105 and the first threshold value Y1 decreases. The correction will end.

  FIG. 4 is a diagram exemplifying an operation region in which a process for reducing and correcting the first threshold value according to the occurrence state of the combustion pressure vibration is executed. The threshold value NE1 related to the rotational speed is 5000 rpm, and the threshold value KL1 related to the load factor. Represents 80%.

  When the operating state of the engine 3 belongs to the operating region in the shaded area in FIG. 4, the ratio C at which the detected value X of the natural vibration amplitude of the combustion pressure vibration exceeds the second threshold value X1 becomes the third threshold value C1. If exceeded, the first threshold value Y1 used for determining the occurrence of knocking in this operating region is corrected to Y1 ′ (<Y1).

  FIG. 5 shows a six-cylinder engine in which a second threshold value X1 related to the amplitude of the natural vibration of the combustion pressure vibration is set as a predetermined value, and the amplitude X of the natural vibration of the combustion pressure vibration exceeds the second threshold value X1. The ratio of the number of times of occurrence and the presence or absence of failure of the piston 14 are shown.

  As shown in FIG. 5, when the ratio that the amplitude X of the natural vibration of the combustion pressure vibration is larger than the second threshold value X1 is more than 2%, the piston 14 has failed due to the combustion pressure vibration. On the other hand, when the ratio of the amplitude X of the natural vibration of the combustion pressure vibration being larger than the second threshold value X1 is less than 2%, the piston 14 did not fail even if such strong combustion pressure vibration occurred.

  Therefore, in the test conditions of FIG. 5, by setting the third threshold C1 to 0.02, it is caused by the combustion pressure oscillation accompanying the occurrence of knocking at a level that is not determined as knocking in the high rotation high load operation region. And it turned out that it can suppress that durability and reliability of the engine 3 fall. In addition, the numerical value of each threshold illustrated in FIG.4 and FIG.5 is an example, and this invention is not limited only to these.

As described above, the knock detection device for an internal combustion engine according to this embodiment includes the vibration detection means 1 for detecting the vibration of the cylinder block 12 of the internal combustion engine 3 and the combustion pressure detection for detecting the combustion pressure of the internal combustion engine 3. It is determined that knocking has occurred when the index indicating the degree of variation in the vibration intensity Y in the frequency range specific to knocking among the vibrations detected by the means 2 and the vibration detection means 1 is greater than the first threshold Y1. It is determined whether or not the intensity X of the vibration in the frequency range unique to knocking among the vibrations of the combustion pressure detected by the first determination means 15 and the combustion pressure detection means 2 is greater than a predetermined second threshold value X1. The determination by the second determination means 15 and the second determination means 15 is performed a plurality of times, and the vibration intensity X of the combustion pressure is determined to be greater than the second threshold value X1 among the plurality of times. Correction means 15 for performing a correction process for reducing the first threshold Y1 when the ratio C of numbers is larger than a predetermined third threshold C1, and the correction means 15 rotates the internal combustion engine 3. Since the correction process is executed when the number NE is higher than the predetermined threshold NE1, the cylinder block 12 is operated in a high engine speed state in which strong combustion pressure oscillations that cause an excessive load on the internal combustion engine 3 can occur frequently. Even if the value of the index representing the degree of variation in the vibration intensity is equal to or smaller than the first threshold value Y1, the first determination means 15 has knocked if it is larger than the corrected first threshold value Y1 ′. It comes to judge. Then, when it is determined by the first determination means 15 that knocking has occurred, control for retarding the ignition timing of the internal combustion engine 3 and control for making the air-fuel ratio of the internal combustion engine 3 rich. Since the control means 15 for performing at least one of them is provided, the combustion state is controlled so that strong combustion pressure vibrations that cause an excessive load on the internal combustion engine 3 do not occur frequently. Therefore, it is possible to suppress a decrease in durability and reliability of the internal combustion engine 3 even in an operating state at a high rotational speed.

  The above-described embodiment is an example for explaining the present invention, and various modifications can be made to the above-described embodiment without departing from the gist of the present invention. For example, in the above embodiment, an example in which the process for lowering the threshold for knocking determination is performed when knocking with large amplitude of combustion pressure vibration frequently occurs in the operation region of high rotation and high load has been described. The same processing may be performed in the operation region.

  As a means for determining knocking, an index (standard deviation or the like) indicating the degree of variation in vibration intensity may be used. In that case, a standard deviation value may be used as the first threshold value.

DESCRIPTION OF SYMBOLS 1 Vibration sensor 2 Combustion pressure sensor 3 Engine 4 Pressure introduction path 5 Exhaust port 6 Cylinder inner wall surface 7 Cylinder 8 Intake valve 9 Exhaust valve 10 Spark plug 11 Cylinder head 12 Cylinder block 13 Intake port 14 Piston 15 ECU
16 Rotational speed sensor 17 Air flow meter 20 Opening

Claims (4)

Vibration detecting means for detecting vibration of a cylinder block of the internal combustion engine;
Combustion pressure detecting means for detecting the combustion pressure of the internal combustion engine;
A first determination is made as to whether or not knocking has occurred based on a comparison between a predetermined first threshold and the intensity of vibration in a frequency range unique to knocking or the physical quantity correlated therewith among the vibrations detected by the vibration detection means. 1 determination means;
Second determination means for determining whether or not the intensity of the vibration in the frequency range specific to knocking among vibrations of the combustion pressure detected by the combustion pressure detection means is greater than a predetermined second threshold;
The determination by the second determination means is performed a plurality of times, and the ratio of the number of times that the vibration intensity of the combustion pressure is determined to be greater than the second threshold among the plurality of times is greater than a predetermined third threshold. Correcting means for correcting the first threshold value in a direction in which it is easy to determine that knocking has occurred by the first determining means;
A knocking detection device for an internal combustion engine, comprising: In claim 1,
The knocking detection apparatus for an internal combustion engine, wherein the correction means executes the correction process when the rotational speed of the internal combustion engine is higher than a predetermined fourth threshold value. In claim 1 or 2,
The internal combustion engine is a spark ignition internal combustion engine;
Control means for performing at least one of control for retarding the ignition timing of the internal combustion engine and control for making the air-fuel ratio of the internal combustion engine rich when the first determination means determines that knocking has occurred; A knocking detection device for an internal combustion engine, comprising: In any one of Claim 1 to 3,
The first determination means has a predetermined first index value indicating a degree of variation of a detected value in a predetermined period of the intensity of vibration in a frequency range unique to knocking among vibrations detected by the vibration detection means. If it is larger than the threshold, it is determined that knocking has occurred,
The knocking detection apparatus for an internal combustion engine, wherein the correction processing by the correction means is correction for reducing the first threshold value.

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