JPH0465638A - Knocking detector for engine - Google Patents

Abstract

PURPOSE:To improve accuracy for a knock detection by calculating a vibration level with taking the distance between the position where a vibration detecting means is arranged and each air cylinder into consideration, and deciding the generation of knocking in accordance therewith. CONSTITUTION:The vibration of engine is detected by the vibration detecting means 5 and this detected signal is subjected to frequency analysis by a frequency analyzing means 9 wherein plural vibration modes can be obtained. The vibration levels of obtained plural vibration modes are calculated by an arithmetic means 11 with taking the distances from the vibration detecting means into consideration for each air cylinder, then the knocking is decided by a knock deciding means 13 in accordance with the calculated vibration levels. In this case, even if the distances from the arranged position for a knock sensor to each air cylinder are different, the vibration detected values are corrected after taking these distances into consideration, e.g., even for the air cylinder positioned far from the knock sensor, the detecting vibration signal is made to one close to the actual vibration level, then the detection accuracy is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a knocking detection device for detecting engine knocking.

(Prior Art) In general, engine knocking, which is caused by compression ignition of unburned gas in the combustion chamber, causes a decrease in output and thermal efficiency. Therefore, countermeasures must be taken to prevent knocking, but methods such as increasing the octane number and lowering the end gas temperature and pressure are not sufficient. A knock sensor is installed to detect the occurrence of knock, and based on this, the amount of advance is controlled to delay the ignition timing.

An engine knocking detection device equipped with such a knock sensor is described in Japanese Patent Laid-Open No. 64-54227. This involves passing the vibration signal detected by the knock sensor through a band-pass filter that passes it in a predetermined frequency band, and comparing the passed vibration signal with a reference value corresponding to when a knock occurs to determine whether a knock has occurred. In response to the output signal of the knock sensor, the second band is narrowed so that the frequency of the knock vibration falls within the passband of the bandpass filter. The reason for setting the frequency passband of the bandpass filter narrowly is
When the passband is wide, more noise passes through ffi, which lowers the S/N ratio (signal/noise ratio), making it difficult to detect the occurrence of minute knocks and lowering the detection accuracy.

In this case, the bandpass filter is provided with one knock control filter whose band changes and two band change filters, and the frequency pass bands of these three bandpass filters are determined by the band change or the knock control filter. Since they are based on the peak values of the output values of the three bandpass filters after knock detection, they overlap with each other. When changing the band, the center frequency of each filter is weighted by the peak level of the engine vibration signal that has passed through each bandpass filter to find the average frequency, and this average frequency is used as the actual knock frequency. This is the center frequency of the control filter.

(Problem to be solved by the invention) However, although such conventional engine knock detection devices can reduce the amount of noise passing through by narrowing the frequency band of the knock control filter, Since knock occurrence is a prerequisite, the knock frequency does not necessarily fall within a narrowly set frequency band, and knock detection accuracy is not sufficient.

In addition, in a multi-cylinder engine, for example, an 8-cylinder engine in which each cylinder is arranged in two cylinder groups of 4 cylinders on the left and right as shown in Figure 11, the distance from the knock sensor installation position to each cylinder is In particular, for cylinders located far from the knock sensor, the detected vibration signal will be lower than the actual vibration level, and even if knocking occurs, it may not be detected. 12(a), (b), and (c) are A in FIG. 11.

Shows the S/N ratio (signal/noise ratio) when knocking is forcibly generated in each cylinder 1 to 8 when knock sensors are installed in each position of B and C (A side is the front of the engine). According to this, the vibration level of a cylinder located far from the knock sensor, for example, when the knock sensor is installed at position A, as shown in FIG. 12(a), 5.
The vibration level of each cylinder of 6.78 is low despite the occurrence of knock. The data in Figure 12 indicates that the engine rotation speed is 200 Or pm and the vibration frequency is 12KH.
This is what happened when z. Figure 13(a)(b),(c)
is the engine rotation speed is 4000 rpm and the vibration frequency is 12
The value at KHz is shown.

The present invention has been made in view of these conventional problems and aims to further improve knock detection accuracy.

[Configuration of the Invention (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention includes a vibration detecting means 5 for detecting vibrations of a multi-cylinder engine 1, and a vibration detecting means 5 for detecting vibrations of a multi-cylinder engine 1, as shown in FIG. A frequency analysis means 9 that frequency-analyzes the vibration signal detected by the means 5 to obtain a plurality of vibration modes, and a distance from the vibration detection means for each cylinder for the plurality of vibration modes obtained by the frequency analysis means 9. The vibration level calculation means 11 calculates the vibration level in consideration of the vibration level calculation means 11, and the knock determination means 13 determines knocking based on the vibration level calculated by the vibration level calculation means 11.

(Operation) Engine vibration is detected by the vibration detection means 5, and this detection signal is frequency analyzed by the frequency analysis means 9 to obtain a plurality of vibration modes. For the plurality of vibration modes obtained, the vibration level is calculated for each cylinder by the vibration level calculating means 11 taking into consideration the distance from the vibration detecting means, and based on the calculated vibration level, the knock determining means 13 or the knocking Make a judgment.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

A multi-cylinder engine 1 used for a vehicle, as shown in FIG. 2, is a V-type 8-cylinder engine in which each cylinder is divided into two groups of four cylinders on the left and right banks, as shown in FIG. In FIG. 3, the upper side is the front of the engine), and the engine 1 is equipped with a crank angle sensor 3 for detecting the engine rotation speed, and a knock sensor 5 as a vibration detector 8 means for detecting engine vibration. The knock sensor 5 converts, for example, engine vibration into an electrical signal using a piezoelectric element, and the engine vibration signal detected thereby is input to the control device 7. A detection signal from the crank angle sensor 3 is also input to the control device 7.

The control device 7 includes a bandpass filter 9 as a frequency analysis means, a vibration level calculation circuit 11 as a vibration level calculation means, and a knock determination circuit 1 as a knock determination means.
3. The bandpass filter 9 passes the vibration signal detected by the knock sensor 5 in a predetermined frequency band, and performs frequency analysis as shown in FIG. 4, for example. FIG. 4 shows an example of frequency analysis when a knock occurs when the engine speed is 200 rpm. The vibration level calculation circuit 11 calculates vibration modes fl, f2, . f3. For f4f5, the actual vibration level is calculated taking into account the engine speed at that time and the distance between the position where the knock sensor 5 is installed and each cylinder at the time of ignition.

Therefore, the distance between the knock sensor 5 and each cylinder is stored in advance in a memory (ROM, not shown) of the control device 7. The above vibration mode fl.

f2. f3. f4. f5 is a value determined by the bore diameter of the cylinder, and if the bore diameters are the same, the multi-values of these vibration modes are the same. The knock determination circuit 13 compares the vibration level calculated by the vibration level calculation circuit 11 with a reference signal generated from the knock sensor output during non-knocking to determine knocking.

The output signal of the control device 7 is input to the ignition timing control circuit 15, and the ignition timing control circuit 15 performs ignition timing control on the ignition plug (not shown) of the engine 1 based on this input signal.

Next, the operation of the engine knocking detection device having the above configuration will be explained based on the flowchart of FIG. First, the engine speed Ne is read by the crank angle sensor 3 (step 101), and the ignition cylinder is determined (step 103). The ignition cylinder is determined by reading the ignition signal sent to the spark plug provided in each cylinder. Next, the vibration of the engine 1 is detected by the knock sensor 5 (step 105), and the detected vibration signal St is frequency-analyzed through the band-pass filter 9 as shown in FIG. 4 (step 107), and the resulting plural frequencies are The knock vibration mode of the band Mij (fl.

f2. f3. f4. f5) is loaded (step 1
09).

Next, a knock level S1j is calculated based on the following equation based on the read knock vibration mode Mij, the distance fit between the knock sensor 5 and the ignition cylinder, and the engine rotational speed Ne (step 111).

S ij-MijX (ff i ) AHere, i is the cylinder number, and j is the frequency mode (fl, f2.f3.f
4. f5). Therefore, there are five knock vibration modes Mij to be read for each cylinder, for example, for the cylinder number 1, Ml fl , M
l f2. Ml f3.

M1f4. Mlf5 exists, and accordingly, five knock levels Sij exist for each cylinder. In addition, A is an index determined by the engine speed Ne, frequency mode j, and ignition cylinder, and the relationship between these is shown in Figure 6 (a
), (b). 6(a) shows experimental data for the left bank cylinders (i-1, 3, 5, 7) in FIG. 3, and FIG. 6(b) shows the experimental data for the right bank cylinders (i-1, 3, 5, 7) in
+ -2, 4, 6, -8).

According to this, as the engine speed Ne increases, the index A
is getting smaller. This is because as the engine speed Ne increases, the knock vibration mode Mij also increases due to the influence of noise, so if (1i) A, that is, A remains a fixed value, the actual knock detection value will be far from the actual knock detection value. This is because the index A is made smaller to achieve matching.

The calculated knock level Sij is compared with a reference value S oij, and based on this, a knocking determination is made (step 113). The reference value 5oij is the engine rotation speed Ne
, is a value determined by the frequency mode J and the ignition cylinder, and in relation to the engine speed Ne, it should be set so that it increases as the engine speed Ne increases, as shown by the curve shown in Figure 7. be. This is because noise increases as the engine speed Ne increases. The reference value S ojj is determined by taking the average of a predetermined number of cycles in a non-knocking state for each frequency mode j, or
Alternatively, the value may be stored in memory in advance.

When determining knocking, it is assumed that knocking has occurred when the knock level Sij is greater than the reference value Soij, and in the next step 115, the ignition timing control circuit 1
5, the ignition advance angle ff1 (ADVi) of the spark plug is reduced by a predetermined amount and retarded, thereby suppressing knocking. When the knock level SIJ is less than the reference [5 oij, the ignition advance amount (ADVi) is compared with the minimum ignition advance angle (M B T ) necessary to generate the maximum shaft torque (step 117), and ADVi 5M When BT is selected, the advance angle remains the same (step 119), and ADVi
When <MBT, the advance angle amount (ADVi) is added by a predetermined amount to perform advance angle control (step 121).

The knock determination in step 113 is performed for five vibration motors for each cylinder. For example, the knock level Slj and reference value S o in the five vibration modes of the No. 1 cylinder
lj respectively, and out of these five comparison results, S
If there are many vibration modes satisfying ij≧S oij (that is, majority decision), or if even one of the vibration modes satisfies the condition Sij≧S oij, it is determined that knocking has occurred. In addition, the sum of the five knock levels Sij (S 1j+ S 2j+
S 3j + S 4j + S 5j) and the reference value S
A knock may be determined by comparing with a value five times oij (5XSoij).

FIGS. 8(a), (b), and (c) are A of FIG. 10,
This figure shows the S/N ratio (signal/noise ratio) when knock occurs when knock is forcibly generated in each cylinder 1 to 8 when knock sensors are installed at each position of B and C. . According to this, the vibration level of each cylinder is approximately the same level regardless of the distance from the knock sensor. This data is based on an engine speed of 2000 rpm.
This is when the vibration frequency is 12KHz (corresponding to vibration mode -f3). Figure 9 (a), (b), (c)
The engine speed is 4000 rpm and the vibration frequency is 12.
The value at KHz is shown. Even in this case, the vibration level between each cylinder maintains a substantially constant level, although it is somewhat inferior to that in FIG.

In this way, even if the distance from the installation position of the knock sensor to each cylinder is different, the vibration detection value is corrected after taking this distance into account, so for example, even for a cylinder located far from the knock sensor, The detected vibration signal becomes close to the actual vibration level, improving detection accuracy.

Further, the calculated knock level Sij may be weighted by multiplying the weighting coefficient Bj to emphasize the vibration frequency to be detected, thereby performing knock detection more accurately. Weighting factor B
j is the five vibration modes fl, f as shown in FIG.
2. f3. f4. It is a value determined according to the engine rotation speed Ne for each f5, and is constant regardless of f3, f4 or the rotation speed, and fl
, f2 become smaller as the rotational speed increases, and f5 becomes larger as the rotational speed increases. The knock level Lij obtained thereby is expressed by the following equation.

L ij= B I S il+ B 2 S i2+
B 3 Si3+B4 Si4+B5 Si5 By performing the weighting as described above, an accurate knock signal corresponding to the rotation speed can be obtained, and more advanced control is possible.

[Effects of the Invention] As described above, according to the present invention, the position where the vibration detection means is installed and the relationship between each cylinder and the plurality of vibration modes obtained by frequency analysis of the vibration signal by the vibration detection means are determined. Since the vibration level is calculated in consideration of the distance between and the occurrence of knocking is determined based on this, the accuracy of knock detection can be improved.

[Brief explanation of the drawing]

Fig. 1 is a diagram corresponding to the claims of this invention, Fig. 2 is a block diagram showing an embodiment of the invention, Fig. 3 is a state diagram showing how the knock sensor is installed on the engine, and Fig. 4 is a diagram showing the engine rotation speed. Fig. 5 is a flowchart showing the control operation, Fig. 6 is a characteristic diagram of each frequency-analyzed vibration mode, and Fig. 7 is a diagram showing an example of frequency analysis when the engine speed is 200 Orpm. Characteristic diagram showing the vibration level reference value, Figure 8 shows the engine speed at 200 rpm.
An explanatory diagram of the S/N ratio when knock is forcibly generated in each cylinder in Figure 9. Figure 9 shows the case where knock is forcibly generated in each cylinder at an engine speed of 4000 rpm, m. An explanatory diagram of the S/N ratio level when
Fig. 10 Correlation diagram between engine speed and weighting coefficient, Fig. 11
The figure shows the installation state of the knock sensor to determine the S/N ratio and specific gravity due to the difference in the position. Figure 12 shows the engine speed with the conventional device.
An explanatory diagram of the S/N ratio ratio when knock is forcibly generated in each cylinder at 0 rpm. Figure 13 is an explanatory diagram of the S/N ratio ratio when knock is forcibly generated in each cylinder at 0 rpm. S/N when generated in
It is an explanatory diagram showing specific level and specific gravity. 1...Multi-cylinder engine 5...Vibration detection means 9...Frequency analysis means 11...Vibration level calculation means 13...Knock determination means

Claims (2)

[Claims] (1) A vibration detection means for detecting vibrations of a multi-cylinder engine, a frequency analysis means for frequency-analyzing the vibration signal detected by the vibration detection means so as to obtain a plurality of vibration modes, and a plurality of vibration modes obtained by the frequency analysis means. Vibration level calculation means for calculating a vibration level for each cylinder in consideration of the distance from the vibration detection means for each vibration mode, and knock determination means for determining knocking based on the vibration level calculated by the vibration level calculation means. An engine knocking detection device comprising: (2) The engine according to claim 1, wherein the knock determining means is configured to weight the vibration level calculated by the vibration level calculating means according to the rotational state of the engine to determine the occurrence of knocking. Knocking detection device.