JPH0326778B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a knocking determination method for an internal combustion engine, and particularly to a method for determining knocking in an internal combustion engine, and in particular, a determination level determined based on a peak value of engine vibration and a background level of engine vibration. The present invention relates to an improvement in a method for determining whether knocking occurs by comparison.

[Conventional technology]

In determining whether or not knocking, which is air column vibration that occurs due to self-ignition of end gas in a cylinder, has occurred, a predetermined crank angle range (for example, 10° CA ATDC to 50° CA゜CA
It is known that the determination is made by comparing the peak value A of engine vibration at the engine vibration (ATDC) with the relative judgment level KB, which is obtained by multiplying the level of engine vibration not caused by knocking, that is, the background level B, by a constant K. . Here, the peak value A is determined by attaching a knocking sensor consisting of a piezoelectric element, a magnetostrictive element, etc. that converts vibration into an electric signal to the cylinder block, and measuring the knocking-specific frequency band (6 to 8 KHz).
The peak value is obtained by inputting the electric signal to a peak hold circuit through a band pass filter through which the signal can pass, and holding the peak value in a predetermined crank angle range. Also, relative judgment level KB
is obtained by multiplying a value (background level) B obtained by integrating an electric signal corresponding to vibrations not caused by knocking by an integrating circuit by a constant K. As a result, even if the level of the peak value A related to the presence or absence of knocking changes due to variations in the output characteristics of the knocking sensor or changes over time, the background level changes accordingly, and the relative judgment level also changes. Since the value changes, it is possible to determine the presence or absence of knotting with high accuracy.

However, in such conventional knocking determination methods, when the background level increases due to noise such as vibration of the crankshaft or camshaft or valve hitting noise, the relative determination level increases, and as a result, even though knocking occurs, the background level increases. There was a problem that it could not be determined. For this reason, in addition to the knocking determination method described above, Japanese Patent Application No. 150096/1983 discloses a method of determining the presence or absence of knocking by using an absolute determination level that is not affected by changes in the background level. According to this method, in addition to the above-mentioned relative judgment level, an absolute judgment level that is not affected by changes in the background level is used, so that the relative judgment level KB becomes higher than the peak value A due to noise, and knocking does not occur. Even when it is determined that knocking has occurred, the presence or absence of knocking can be determined by comparing the peak value A and the absolute determination level C.

[Problem to be solved by the invention]

However, since the knocking sensor is usually mounted on the side wall of the cylinder block at the center, the distance from the knocking sensor to each cylinder is different, and even if knocking of the same intensity occurs in each cylinder, the knocking will cause vibrations. It is attenuated in proportion to the distance, and the detected peak value A differs for each cylinder. Therefore, it is necessary to set the absolute determination level C to avoid false detection for the cylinder where the largest peak value is detected, and by setting it in this way, it is possible to determine whether or not knocking has occurred in the cylinder where the detected peak value is small. A problem arises in that it cannot be determined. Furthermore, since the wall thickness of each cylinder may vary during the cylinder block manufacturing stage, the propagation state of vibration due to knocking differs between cylinders, resulting in cylinders in which it is difficult to detect the peak value and cylinders in which it is easy to detect. Therefore, even if a plurality of knocking sensors are provided and the distances from the sensors to each cylinder are made the same, the above problem cannot be solved.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a knocking determination method for an internal combustion engine that prevents false knocking determinations from occurring by setting an absolute determination level for each cylinder. shall be.

[Means to solve the problem]

In order to achieve the above object, the present invention converts engine vibration into an electrical signal, and performs a relative judgment based on the peak value of the electrical signal in a predetermined crank angle range after each cylinder ignition and the integrated value of the electrical signal. The system is configured to determine whether or not knocking has occurred by comparing the peak value of the electric signal with an absolute determination level predetermined for each cylinder.

[Operation] According to the above configuration, in addition to the relative judgment level, an absolute judgment level is set for each cylinder, so even if the relative judgment level becomes high due to noise and it becomes impossible to judge knocking, the By comparing with the absolute judgment level, it is possible to prevent erroneous judgments caused by variations in peak values caused by differences in the propagation state of knocking vibrations due to differences in the distance from each cylinder to the knocking sensor or the shape of the cylinder block. It is possible to make a notsking judgment.

〔Example〕

Next, an internal combustion engine (engine) to which the present invention is applied
An example will be explained with reference to FIG. This engine is controlled by an electronic control circuit such as a microcomputer, and as shown in the figure, is equipped with an air flow meter 2 as an intake air amount sensor downstream of an air cleaner (not shown). The air flow meter 2 includes a compensation plate 2A rotatably provided within the damping chamber.
and a potentiometer 2B that detects the opening degree of the compensation plate 2A. Therefore, the amount of intake air is determined by potentiometer 2B.
It is detected from the voltage output from the Further, an intake air temperature sensor 4 is provided near the air flow meter 2 to detect the temperature of intake air.

A throttle valve 6 is arranged downstream of the air flow meter 2, and downstream of the throttle valve 6,
A surge tank 8 is provided. An intake manifold 10 is connected to the surge tank 8, and a fuel injection valve 12 is disposed protruding into the intake manifold 10. The intake manifold 10 is an engine main body 14
The combustion chamber 14A of the engine is connected to the combustion chamber 14A of the engine.
4A is connected via an exhaust manifold 16 to a catalytic converter (not shown) filled with a three-way catalyst. And in the engine body 14,
A knocking sensor 18 is provided which is composed of a magnetostrictive element or the like and detects vibrations of the engine due to combustion. In the case of a six-cylinder engine, this knocking sensor 18 is installed between the third cylinder #3 and the fourth cylinder #4, as shown in FIG. In addition, 2
0 is a spark plug, 22 is an O ₂ sensor, and 24 is a coolant temperature sensor that detects the engine coolant temperature.

Spark plug 2 attached to engine body 14
0 is connected to a distributor 26, and the distributor 26 is connected to an igniter 28. The distributor 26 is provided with a cylinder discrimination sensor 30 and an engine rotation angle sensor 32, each of which includes a pickup fixed to the distributor housing and a signal rotor fixed to the distributor shaft. . This cylinder discrimination sensor 30 outputs a cylinder discrimination signal to an electronic control circuit 34 composed of a microcomputer or the like every 720 degrees of the crank angle, and the engine rotation angle sensor 32 outputs a cylinder discrimination signal based on the crank angle every 30 degrees of the crank angle. A position signal is output to the electronic control circuit 34.

As shown in FIG. 3, the electronic control circuit 34 includes a random access memory (RAM) 36, a read-only memory (ROM) 38, a central processing unit (CPU) 40, a clock (CLOCK) 41,
First input/output port 42, second input/output port 4
4, includes a first output port 46 and a second output port 48, RAM 36, ROM 3
8. The CPU 40, CLOCK 41, first input/output port 42, second input/output port 44, first output port 46, and second output port 48 are connected by a bus 50 such as a data bus or a control bus. There is.

An air flow meter 2, a cooling water temperature sensor 24, an intake air temperature sensor 4, etc. are connected to the first input/output port 42 via a buffer (not shown), a multiplexer 54, and an analog/digital (A/D) converter 56. has been done. This multiplexer 54
The A/D converter 56 is controlled by a control signal output from the first input/output port 42.
A comparator 62 is connected to the second input/output port 44.
An O ₂ sensor 22 is connected to the cylinder through a waveform shaping circuit 64, and a cylinder discrimination sensor 30 and an engine rotation angle sensor 32 are connected through a waveform shaping circuit 64. Furthermore, the knocking sensor 18 is connected to the second input/output port 44 via a bandpass filter 60, a peak hold circuit 61, a channel switching circuit 66, and an A/D converter 68. This bandpass filter is connected to a channel switching circuit 66 via an integrating circuit 63. This channel switching circuit 66 includes a peak hold circuit 61.
A control signal for inputting either the output of the integrator circuit 63 or the output of the integrating circuit 63 to the A/D converter 68 is
A reset signal and a gate signal are input to the peak hold circuit 61 from the second input/output port 44 .

Further, the first output port 46 is connected to the igniter 28 via a drive circuit 70, and the second output port 48 is connected to the fuel injector 12 via a drive circuit 72.
It is connected to the.

The ROM 38 of the electronic control circuit 34 stores a basic ignition advance map expressed by engine speed and intake air amount (or load), and absolute judgment level C data set for each cylinder as shown in Fig. 4. etc. are stored in advance. The data in Figure 4 shows the absolute judgment level C when a 6-cylinder engine is installed with a knocking sensor as shown in Figure 2, and does not take into account the wall thickness of the cylinder block. The same absolute determination level is determined for each of the cylinder #1 and the sixth cylinder #6, the second cylinder #2 and the fifth cylinder #5, and the third cylinder #3 and the fourth cylinder #4. In addition, when considering the wall thickness of the cylinder block, each absolute determination level is determined by experiment.

Next, an embodiment in which the present invention is applied to the engine as described above will be described in detail. In addition,
In describing the embodiments of the present invention, routines such as fuel injection control, air-fuel ratio control, ignition timing control, etc. are the same as conventional routines, so their explanations will be omitted.

Figure 5 shows a predetermined crank angle (for example, 90° CA).
BTDC), and in step 80, it is determined which cylinder number the ignited cylinder is based on the cylinder discrimination signal and the crank angle reference position signal. In the next step 82, as in the conventional case, the gate provided in the peak hold circuit is opened for a predetermined crank angle to hold the peak value A of the electrical signal output from the knocking sensor. is AD converted and stored in a predetermined area of RAM. In addition, in the next step 84, the above gate is closed and the background level B obtained by integrating the electric signal is AD converted.
Store in a specified area of RAM. Next step 86
Now, compare the relative judgment level KB, which is the background level B multiplied by the constant K, with the peak value A, and when the peak value A exceeds the relative judgment level KB, it is determined that knocking has occurred, and step 94 is performed.
A knocking flag f is set in the step.

On the other hand, when the peak value A becomes less than the relative judgment level KB, the absolute judgment level C for the currently ignited cylinder is read from the ROM in step 88, and the peak value A and the absolute judgment level C are compared in step 90. Then, when the peak value exceeds the absolute judgment level C, it is determined that knocking has occurred and a knocking flag f is set in step 94, and when the peak value is below the absolute judgment level C, knocking has occurred. It is determined that there is no knocking flag f in step 92 and the knocking flag f is reset.

In the next routine, the igniter is controlled to retard the ignition timing when knocking occurs and to advance the ignition timing when knocking does not occur, based on the knocking flag f reset as described above.

Although the above example describes an example in which the present invention is applied to an engine that detects the amount of intake air using an air flow meter, the present invention is not limited to this. It is also possible to apply this method to an engine that detects.

〔Effect of the invention〕

According to the present invention, even if the relative judgment level increases abnormally, the absolute judgment level is set for each cylinder, so by comparing and judging with the electric signal peak value, the difference in vibration propagation conditions related to knocking can be determined. This has the effect of preventing erroneous determinations due to variations in the peak values of the electrical signals and making it possible to reliably determine knocking.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of an engine to which the present invention is applied, FIG. 2 is an explanatory diagram showing how the knocking sensor is installed, and FIG. 3 is a block diagram showing the electronic control circuit of FIG. FIG. 4 is an explanatory diagram showing the storage state of the absolute judgment level, and FIG. 5 is a flowchart showing the processing routine in the embodiment of the present invention. 18... Notking sensor, 26... Distributor, 34... Electronic control circuit.

Claims (1)

[Claims] 1 Convert engine vibration into an electrical signal, compare the peak value of the electrical signal in a predetermined crank angle range after each cylinder ignition with a relative judgment level determined based on the integrated value of the electrical signal, and A knocking determination method for an internal combustion engine that determines whether knocking has occurred by comparing a peak value with an absolute determination level predetermined for each cylinder.