JP3487169B2 - Knock detection device for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a knocking detection device for an internal combustion engine. 2. Description of the Related Art It is known that knocking easily occurs when the combustion pressure is high. Japanese Patent Application Laid-Open No. 63-143360 proposes that when knocking is detected, the opening of the throttle valve is reduced to reduce the amount of intake air and the combustion pressure is reduced to limit the occurrence of knocking. Have been. [0003] Knocking generates vibration having a vibration level peak at a plurality of specific frequencies determined by the shape of the combustion chamber and the like. Generally, knocking is detected by using a vibration sensor attached to a cylinder block to detect a vibration level at one detection frequency selected from a plurality of specific frequencies. As a detection frequency of the vibration sensor, a specific frequency on the high frequency side is selected in consideration of the fact that background noise becomes lower on the higher frequency side in order to enhance the detection accuracy of knocking. [0005] In the prior art described above, knocking is reliably detected by the vibration sensor.
When knocking is detected, the opening of the throttle valve can be controlled to be small. However, if knocking still occurs even when the opening of the throttle valve is reduced, the vibration level at a specific frequency on the high frequency side of the knocking vibration decreases due to a decrease in combustion pressure. In this case, knocking cannot be reliably detected. Thereby, knocking may continue to occur without taking any measures. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a knocking detection device used in an internal combustion engine having a throttle valve control means for limiting knocking by controlling the opening of the throttle valve when knocking occurs. It is to be able to reliably detect knocking before and after. [0007] A knocking detection apparatus for an internal combustion engine according to the present invention is used in an internal combustion engine having throttle valve control means for limiting knocking by controlling the opening of the throttle valve when knocking occurs. A knocking detection device, comprising: detection means capable of detecting a vibration level at at least two detection frequencies on a high frequency side and a low frequency side; and a vibration level at a detection frequency on the high frequency side which is normally detected by the detection means. And determining means for determining occurrence of knocking based on a vibration level at the detection frequency on the low frequency side detected by the detection means when the opening of the throttle valve is equal to or less than a predetermined value. It is characterized by having. FIG. 1 is a schematic sectional view showing an internal combustion engine equipped with a knocking detection device according to the present invention. In FIG. 1, reference numeral 1 denotes a piston, 2 denotes an intake passage leading to the cylinder via an intake valve 3, and 4 denotes an exhaust passage leading to the cylinder via an exhaust valve 5. A surge tank 2a is provided in the intake passage 2, and a throttle valve 6 is disposed downstream of the surge tank 2a. The throttle valve 6 is not mechanically connected to the accelerator pedal, but is a step motor 6a.
Thus, the opening degree can be freely controlled. 20
Is a control device for controlling the opening of the throttle valve 6 via the step motor 6a. The control device 20 is connected with an opening sensor 21 for detecting the actual opening of the throttle valve 6, an accelerator pedal stroke sensor, a rotation sensor, a cooling water temperature sensor and the like for detecting an engine operating state. ing. The control device 20 also functions as a knocking detection device, and is connected to a vibration sensor 22 that is attached to the cylinder block and detects vibration. The vibration sensor 22 is a non-resonance type vibration sensor, and detects the vibration levels L1 and L2 at the first detection frequency F1 on the high frequency side and the second detection frequency F2 on the low frequency side via a band-pass filter. This is output to the control device 20. FIG. 2 is a flowchart for controlling the opening of the throttle valve 6 and detecting knocking by the control device 20. This flowchart is repeated every predetermined period, which will be described below. First, in step 101, an accelerator pedal stroke detected from an accelerator pedal stroke sensor as an engine load, an engine speed detected from a rotation sensor, and a cooling water temperature detected from a cooling water temperature sensor as an engine temperature. The target opening TAT of the throttle valve 6 is determined based on a map or the like based on this, and the stepping motor 6a is operated so that the target opening TAT is realized. Next, in step 102, the actual opening TAA of the throttle valve 6 is detected by the opening sensor 21. Next, at step 103, it is determined whether or not a flag F, which will be described in detail later, is "1". Initially, the flag F is reset to 0, so this determination is denied, and the process proceeds to step 105 without passing through step 104. In step 105, it is determined whether or not the actual opening degree TAA detected in step 102 is equal to or greater than a first predetermined value TA1. Actual opening degree T of throttle valve 6
When AA is relatively large, this judgment is affirmed, the flag F is set to 0 in step 106, and
At 7, the count value C is set to 0, and the routine proceeds to step 108. In step 108, the vibration sensor 22
It is determined whether or not knocking has occurred based on the vibration level L1 at the first detection frequency F1 on the high frequency side detected by the above. FIG. 3A is a graph showing the vibration level of the cylinder block at each frequency when the actual opening TAA of the throttle valve 6 is relatively large. The solid line is when knocking has not occurred, that is, the background noise for knocking detection. The vibration level of the background noise is lower on the higher frequency side. When knocking occurs, the vibration level of each frequency changes as shown by a dotted line.
Vibration level peaks occur at three specific frequencies. The value used for knocking detection is the ratio of the vibration level at a specific frequency to the background noise, that is, SN
Ratio. Accordingly, when the opening of the throttle valve 6 is relatively large, in order to enhance the knocking detection accuracy, of the three specific frequencies, in addition to the lowest background noise, the vibration level increased by knocking is the highest. It is preferable to use the specific frequency F1 on the high frequency side as the detection frequency to increase the SN ratio when knocking occurs. Accordingly, in step 108, based on the vibration level L1 at the first detection frequency F1, the first
It is assumed that knocking has occurred when the SN ratio between the average value (or smoothed value) of the past multiple vibration levels at the detection frequency F1 and the background noise of the map data at the first detection frequency F1 exceeds the threshold value. Is determined.
When it is determined that knocking has not occurred, the process ends as it is. When it is determined that knocking has occurred, the process proceeds to step 109, where the actual opening TAA of the throttle valve 6 is reduced by the first predetermined opening a. Step 1
Return to 02. If the opening of the throttle valve 6 is reduced, knocking is less likely to occur because the amount of intake air decreases and the combustion pressure decreases. Thereby, step 1 again
At 08, it is determined whether or not knocking has occurred, and the opening of the throttle valve 6 is gradually reduced until it is determined that knocking has not occurred. In this manner, the suppression of the knocking that reduces the intake air amount is different from the suppression of the knocking that retards the ignition timing because the combustion is not deteriorated, so that the fuel consumption rate and the exhaust emission do not deteriorate. If the actual opening degree TAA of the throttle valve 6 is reduced to some extent, the determination at step 105 is denied and the routine proceeds to step 110. In step 110, the actual opening degree TAA of the throttle valve 6 is set to the second predetermined value TA2.
It is determined whether or not: When the opening of the throttle valve 6 is not so large, this determination is affirmed and the routine proceeds to step 111, where the flag F is set to 1, and in step 112, the count value C is increased by 1. Then, the process proceeds to a step 113, wherein the second detection frequency F2 on the low frequency side detected by the vibration sensor 22 is used.
Is determined based on the vibration level L2 at. FIG. 3B is a graph showing the vibration level of the cylinder block at each frequency when the actual opening TAA of the throttle valve 6 is not so large. Similarly to FIG. 3A, a solid line indicates a case where knocking has not occurred, that is, a background noise corresponding to knocking detection, and a dotted line indicates a case where knocking has occurred. Compared to FIG. 3A in which the opening of the throttle valve 6 is relatively large, when the opening of the throttle valve 6 is not so large, the background noise decreases due to the decrease in the combustion pressure. And the vibration level increased by knocking at the above three specific frequencies is also reduced. In particular, at the specific frequency F1 on the high frequency side, the vibration level of this increase becomes the smallest. In this case, if the specific frequency F1 on the high frequency side is used as the detection frequency, the obtained S / N ratio becomes small, so that it is impossible to accurately determine the occurrence of knocking. Accordingly, in this flowchart, in this case, the specific frequency F2 on the low frequency side where the vibration level increased by knocking is the highest among the three specific frequencies is set as the detection frequency. At the specific frequency F2, the background noise is the largest as compared with the other specific frequencies, but as shown in FIG. 3B, the SN ratio when knocking occurs is the largest. In step 108, the second detection frequency F2
Based on the vibration level L2 at the second detection frequency F
It is determined that knocking has occurred when the SN ratio between the average value (or smoothed value) of the past multiple vibration levels in 2 and the background noise of the map data at the second detection frequency F2 exceeds the site value. You. When it is determined that knocking has not occurred, the process ends as it is. When it is determined that knocking has occurred, the process proceeds to step 114, where the actual opening TAA of the throttle valve 6 is reduced by the second predetermined opening b. Return to step 102 after reducing the size.
When the opening of the throttle valve 6 is not so large, knocking is not likely to occur. Therefore, the second predetermined opening b is smaller than the first predetermined opening a. In the determination of occurrence of knocking in step 108, as described above, since the SN ratio at the time of knocking is relatively large, it is not possible to use the average or smoothed value of the vibration level in calculating the SN ratio. Although it is not particularly necessary, even if the occurrence of knocking is determined based on the SN ratio in which the detected one vibration level is used as it is, the accuracy does not significantly decrease. However, step 1
In the determination of the occurrence of knocking in S13, the SN ratio at the time of occurrence of knocking is relatively small, and it is necessary to use the average value or the smoothed value of the vibration level in calculating the SN ratio in order to maintain the determination accuracy relatively high. It is said. Thus, in the present flowchart, once the vibration level L2 at the second detection frequency F2 is used to determine the occurrence of knocking, the flag F is set to 1 in step 111 and the determination in step 103 is affirmed. , And it is determined in step 104 whether the count value C is greater than n. When this determination is denied, that is, when the knocking occurrence determination at the vibration level L2 at the second detection frequency F2 is not repeated n times, the process proceeds to step 112 regardless of the opening degree of the throttle valve 6, and the count value is determined. C is increased by one, and in step 113, it is determined that knocking has occurred at the vibration level L2 at the second detection frequency F2. Further, in this flowchart, the first predetermined value TA1 and the first predetermined value TA1 are used in order to prevent the detection frequency in the knocking occurrence determination from frequently changing due to the throttle valve opening fluctuating near a single threshold value. When two threshold values TA2 are used and the opening of the throttle valve 6 is between the first predetermined value TA1 and the second predetermined value TA2, whether or not the flag F is 1 in step 115 When this determination is affirmed, the process proceeds to step 112, and when this determination is denied, the process proceeds to step 107, and knocking occurrence determination is performed at the same detection frequency as the previous time. Thereby, even if the opening degree of the throttle valve 6 fluctuates near the first predetermined value TA1, the detection frequency of the knocking occurrence determination is maintained at the first detection frequency,
Further, even if the opening degree of the throttle valve 6 fluctuates in the vicinity of the second predetermined value TA2, the detection frequency for knocking occurrence determination is maintained at the second detection frequency. In this embodiment, the vibration sensor 22
Although a single non-resonant vibration sensor that outputs a vibration level at each of the two detection frequencies via a band-pass filter is used, this does not limit the present invention. It is also possible to use two resonance-type vibration sensors that output respective signals. Further, two or more detection frequencies may be switched in accordance with the opening degree of the throttle valve and used for knocking occurrence determination. As described above, according to the knocking detecting device for an internal combustion engine according to the present invention, the detecting means detects the vibration level at at least two detection frequencies on the high frequency side and the low frequency side, and determines the vibration level. However, normally, the occurrence of knocking is determined based on the vibration level at the detection frequency on the high frequency side, and when the opening of the throttle valve falls below a predetermined value, the occurrence of knocking is determined based on the vibration level at the detection frequency on the low frequency side. Therefore, it is possible to reliably detect knocking at any time, and it is possible to reliably detect knocking by the throttle valve control means even if the opening of the throttle valve is set to a predetermined value or less when knocking occurs. it can.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view of an internal combustion engine equipped with a knocking detection device according to the present invention. FIG. 2 is a flowchart for controlling the opening of a throttle valve and detecting knocking. 3A and 3B are graphs showing a vibration level with respect to a frequency in a cylinder block, wherein FIG. 3A shows a case where the throttle valve opening is relatively large, and FIG. 3B shows a case where the throttle valve opening is not so large. [Description of Signs] 2 ... Intake passage 6 ... Throttle valve 20 ... Control device 21 ... Opening sensor 22 ... Vibration sensor

Claims (1)

Claims: 1. A knocking detection device used in an internal combustion engine having a throttle valve control means for limiting knocking by controlling the opening of a throttle valve when knocking occurs. And detecting means capable of detecting a vibration level at at least two detection frequencies on the low frequency side, and normally determines occurrence of knocking based on a vibration level at the detection frequency on the high frequency side detected by the detection means, An internal combustion engine comprising: a determination unit configured to determine occurrence of knocking based on a vibration level at the detection frequency on the low frequency side detected by the detection unit when the opening of the throttle valve is equal to or less than a predetermined value. Knocking detection device.