JPH037063B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for detecting the occurrence of knocking in an internal combustion engine, and particularly to an improvement in calculating a background value for a comparison criterion value.

[Problems to be solved by conventional technology and invention]

Mechanical vibrations caused by abnormal engine combustion;
In other words, in the knocking detection method in which knocking is detected as an electrical vibration fluctuation using a vibration detection element called a knock sensor, by comparing the amplitude of the electrical signal output from the knock sensor with a comparison reference value, it is possible to determine whether the detected vibration is due to knocking. A determination is made as to whether the object is a real object or not. In this case, the comparison reference value is not fixed to a constant value, but is changed according to an output signal (hereinafter referred to as a background signal) that is considered to be unrelated to the knocking of the knock sensor.
It becomes possible to compensate for variations in the knock sensor, changes over time, and the like.

Conventionally, the above-mentioned reference value based on the background value has been determined by constantly integrating the output amplitude value of the knock sensor using an integrating circuit (for example, Japanese Patent Laid-Open No. 114878/1983). However, if a microcomputer is used to directly replace the function of the above-mentioned integrating circuit, the output amplitude value of the knock sensor is A/D converted and taken in, and then the integral value is calculated in the same way as in the above-mentioned integrating circuit. However, because the processing speed of the A/D converter is slow, it is not possible to A/D convert a sufficient number of signals from the knock sensor, so an integrating circuit is provided as hardware. This results in an increase in equipment cost.

Therefore, the applicant of the present application has proposed a first predetermined crank angle range (background signal detection range: compression stroke
Hold the peak value of the output amplitude value of the knock sensor at 30° CA・BTDC ~ 10° CA・BTDC), convert this into A/D and take it in as the judgment reference value, and
Second predetermined crank angle range (knocking detection range: compression stroke 10° CA/ATDC to 50° CA/ATDC)
It has already been proposed that knocking be detected by holding the peak value of the output amplitude value of the knock sensor, A/D converting it, capturing it as a knocking signal, and comparing it with the above-mentioned criterion value (see: (Gan Sho 56-93954).

However, in the knocking detection method proposed above, although it is preferable that the comparison reference value uses the latest peak value of the knock sensor under the constantly changing engine conditions, it is difficult to judge where the peak value is in the variation. Can not. In other words, the judgment reference value is calculated depending on the current peak value for each ignition, so although it has good followability during transient periods, it is strongly affected by noise etc., and as a result, the judgment reference value is not as high as it should be. This method may not be based on a ground signal, and therefore there is a problem in that the presence or absence of knocking may be incorrectly detected.

On the other hand, in Japanese Patent Application Laid-open No. 54-141180, output amplitude values of a plurality of knock sensors for a predetermined period are stored, and a judgment reference value is calculated based on the average value of these values. Since past output amplitude values and current output amplitude values are treated equally, they are less susceptible to noise, etc., but the ability to follow transients is reduced, which can lead to errors in detecting the presence or absence of knocking. Another problem is that storing multiple output amplitude values increases the capacity of the storage device (RAM).

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a knocking detection device that can perform accurate and reliable knocking detection without increasing the capacity of a storage device.

[Means to solve the problem]

A means for solving the above problem is shown in FIG. That is, in a device for detecting whether or not knocking occurs, a knock sensor comprising at least one vibration detection element that converts mechanical vibration into an amplitude fluctuation of an electric signal is mounted on the engine body of an internal combustion engine, and the knock sensor detects the occurrence of knocking according to the electric signal of the knock sensor. , the peak value detection means detects a peak value a of the amplitude value of the electric signal in a predetermined crank angle range after ignition of at least one cylinder, and the average value calculation means calculates an average value A of the peak values a. It is weighted so that the influence of recent peak values is stronger (for example, A
= (9・A+a)/10) is calculated for each ignition, and the knock judgment reference value calculation means uses the average value A as a background value and multiplies it by predetermined values K and K'(>1) to determine the knock judgment criterion. Calculate the values KA and K′A.
As a result, the comparison means compares the determination reference values KA, K'A' with the above-mentioned peak value a. The presence or absence of knocking is determined according to the comparison result of this comparison means.

[Effect]

According to the above-mentioned means, by appropriately setting the weighting in the average value calculation (the above-mentioned smoothing ratio of 9:1), the average value A that emphasizes the current peak value a and also takes advantage of the past peak value a can be obtained. Obtained for each ignition. Therefore, this average value A is less affected by noise and the like, and followability is maintained even when the average vibration changes moment by moment during a transient period. Furthermore, there is no need to store a plurality of peak values, which contributes to reducing the capacity of the storage device.

〔Example〕

The present invention will be explained in detail below using the drawings.

FIG. 1 schematically shows the overall configuration of a knocking control system as an embodiment of the present invention. In the figure, 10 is a cylinder block of the engine, and 12 is a knock sensor attached to the cylinder block 10. The knock sensor 12 is composed of, for example, a piezoelectric element or an electromagnetic element,
It is well known to convert mechanical vibrations into electrical amplitude fluctuations. In FIG. 1, 14 further indicates a distributor, and this distributor 14 includes crank angle sensors 16 and 18.
is provided. The crank angle sensor 16 is for cylinder discrimination, and if this engine has 6 cylinders, it generates one pulse every time the distributor shaft makes one revolution, that is, every two revolutions of the crankshaft (every 720° CA). occurs. The location of the occurrence is, for example,
It is set like the top dead center of the first cylinder. The crank angle sensor 18 generates 24 pulses each time the distributor shaft rotates, ie, every 30 degrees of crank angle.

Electrical signals from the knock sensor 12 and crank angle sensors 16 and 18 are sent to a control circuit 20. The control circuit 20 is further fed with a signal representing the intake air flow rate from an air flow sensor 24 provided in the intake passage 22 of the engine. on the other hand,
The control circuit 20 outputs an ignition signal to the igniter 26, and the spark current generated by the igniter 26 is distributed to the spark plugs 28 of each cylinder via the distributor 14.

The engine is provided with various other sensors that detect normal operating state parameters, and the control circuit 20 also controls the fuel injection valve 29 and the like.
Since these are not directly related to the present invention, they will be completely omitted in the following description.

FIG. 2 is a block diagram showing an example of the configuration of the control circuit 20 shown in FIG. Air flow sensor 24
The voltage signal from is sent to the analog multiplexer 32 via the buffer 30, selected according to instructions from the microcomputer, and applied to the A/D converter 34, where it is converted into a binary signal.
It is taken into the microcomputer via the input/output port 36.

Pulses at every 720° crank angle from the crank angle sensor 16 are applied to an interrupt request signal forming circuit 40 via a buffer 38. On the other hand, the pulses from the crank angle sensor 18 every 30 degrees of crank angle are:
Interrupt request signal forming circuit 4 via buffer 42
0 and is applied to the speed signal forming circuit 44. The interrupt request signal forming circuit 40 forms various interrupt request signals from pulses at every 720° and every 30° crank angle. These interrupt request signals are applied to the microcomputer via the input/output port 46. The speed signal forming circuit 44 forms a binary signal representing the rotational speed Ne of the engine from the period of pulses every 30 degrees of crank angle.

The formed rotational speed signal is sent to the input/output port 46
is sent to the microcomputer via the

The output signal of the knock sensor 12 is sent to a peak hold circuit 50 via a circuit 48 comprising a buffer for impedance conversion and a bandpass filter whose pass band is a frequency band (7 to 8 kHz) specific to knocking. The peak hold circuit 50 takes in the output signal from the knock sensor 12 and holds the maximum amplitude only when a "1" level signal is applied from the microcomputer via the line 52 and the input/output port 46. conduct. The output of the peak hold circuit 50 is
converted into a binary signal by an A/D converter 54,
It is sent to the microcomputer via the input/output port 46. However, the A/D conversion of the A/D converter 54 starts at the input/output port 46 and the line 56.
This is performed by an A/D conversion activation signal applied from the microcomputer via the microcomputer. Also,
When the A/D conversion is completed, the A/D converter 54
A/D conversion completion notification is sent to the microcomputer via line 58 and input/output port 46.

On the other hand, when an ignition signal is output from the microcomputer to the drive circuit 60 via the input/output port 46, this is converted into a drive signal and the igniter 2
6 is energized, and ignition control is performed according to the duration and duration of the ignition signal.

The microcomputer has the aforementioned input/output ports 36 and 46 and a microprocessor (MPU).
62, random access memory (RAM) 64,
It mainly consists of a read-only memory (ROM) 66, a clock generation circuit (not shown), a memory control circuit, a bus 68 connecting these, etc., and executes various processes according to the control program stored in the ROM 66. do.

3 to 6 are flowcharts showing only the parts particularly related to the present invention among the control contents. According to these processing routines, a peak hold operation of the knock sensor output is performed during a period in which a knock signal is included in the signal from the knock sensor 12 when knocking occurs (knock detection period), and the final value is held as a binary signal. It is captured. Further, the average value of the binary signals taken in each knocking detection period a predetermined number of times is calculated, and this average value is recognized as a background value. A comparison reference value is calculated according to this background value, and the comparison reference value is compared with the binary signal value taken in each knocking detection period to determine whether or not knocking has occurred.

The knocking detection period described above is preferably between 10° CA ATDC and 50° CA during the explosion stroke of each cylinder or a predetermined specific cylinder.
Selected near ATDC.

The contents of the processing routines shown in FIGS. 3 to 6 will be explained in detail below.

A predetermined interrupt request signal is applied from the interrupt request signal forming circuit 40 at a predetermined crank angle position θ ₀ CA of each cylinder or a predetermined specific cylinder, for example, at explosion top dead center or 30° CA BTDC in the compression stroke. Then, the MPU 62 executes the interrupt processing routine shown in FIG. That is, step 7
0, the time t ₁ at which the knocking detection period begins
Calculate. This time _t1 is the time of the timer on the software, and is the crank angle position at which the knocking detection period starts (for example, 10° CA・ATDC).
It is clear that the calculation can be easily performed if the current crank angle position (θ° CA), the current time t ₀ of the timer, and the engine rotational speed Ne are known. Upon completion of step 70, the interrupt routine ends and the program returns to the main routine.

When the soft timer reaches time _t1 , a time interrupt request is generated, which causes the MPU 62 to execute the interrupt processing routine shown in FIG. First step 7
1, the peak hold circuit 50 starts a peak hold operation of the output of the knock sensor 12. This is accomplished by sending a "1" level peak hold instruction signal to peak hold circuit 50 via line 52. Next, in step 72, the time _t2 at which the knocking detection period ends is calculated. Since the crank angle position at which the knocking detection period ends (for example, 50° CA/ATDC) is determined in advance, the calculation method in step 72 is the same as in step 70. Next, in step 73, the A/D converter 54 is instructed to start A/D conversion, and then the process returns to the main routine.

A/D conversion by the A/D converter 54 is completed,
When an interrupt request signal due to completion of A/D conversion is applied via line 58, MPU 62 executes the interrupt processing routine shown in FIG. First, step 74
In step 75, the current A/D converted value A/Di of the output of the peak hold circuit 50 is compared with the previous A/D converted value A/Di _-1 , and then the next steps 75 and 76 are performed.
In , the larger A/D conversion value is assigned to a. The contents of this a are stored in a predetermined area of the RAM 64. In the next step 77, it is determined whether or not the peak hold operation is currently in progress. If it is in operation, the process advances to step 78 and A/D conversion is started again. In this way, in this embodiment, A/D conversion is repeated a plurality of times during one peak hold operation period, and the maximum value thereof is detected. This is done because the peak hold value does not maintain its peak value and "sags" over time. Note that when an excellent peak hold circuit is used to prevent the above-mentioned "sag", the A/D conversion operation only needs to be performed once at the end of each peak hold operation period.

When the soft timer reaches time _t2 , a time interrupt request is generated, which causes the MPU 62 to execute the interrupt processing routine shown in FIG. First, in step 79, the peak hold instruction signal is set to "0".
to end the peak hold operation.
Next, the process proceeds to step 80, where the maximum value of the peak hold values detected during the knocking detection period, that is,
A value a corresponding to the maximum amplitude of the output of the knock sensor 12 during this period stored in the RAM 64, an average value A (i.e. a background value) reflecting each value a in each past ignition cycle, and a constant value K. From this, it is determined whether K·A≧a.
If K・A≧a, it is determined that no knocking has occurred, and the process proceeds to step 81 where the background value A is determined.
is corrected by the current value a. In other words, A←9A+a/10 is calculated. This formula is used to calculate the average value A by weighting so that the influence of the recent value a becomes stronger. That is, in the RAM 64, only the most recent value a and the average value A are stored for the knock sensor output. then
The MPU 62 executes steps 82 to 85. In steps 82 to 85, if knocking has not occurred in the past 10 consecutive ignition cycles, the ignition timing is advanced by Y. That is, in step 82, it is determined whether or not n is 10 or more. If n is less than 10, n is incremented by 1 in step 83, and then this interrupt handling routine is ended. On the other hand, if n is 10 or more, the process proceeds to step 84, where n is reset to zero, and then the process proceeds to step 85. In step 85,
A process is performed to increase the ignition timing advance angle correction value θ by Y. This advance angle correction value θ is used in a well-known ignition timing calculation routine that is executed at every predetermined crank angle position. That is, in the ignition timing calculation processing routine, the optimum ignition timing is calculated from operating condition parameters such as the intake air flow rate Q detected by the air flow sensor 24 and the rotational speed Ne obtained from the rotational speed signal forming circuit 44, and The ignition timing is further corrected using the advance angle correction value θ. Therefore, by performing the process of step 85, the ignition timing (ignition timing of the next ignition cycle) is advanced by Y. Step 8
When the process in step 5 is completed, the process returns to the main routine.

On the other hand, if it is determined in step 80 that K.A<a, that is, if it is determined that knocking has occurred, the process proceeds to step 86, where the advance angle correction value θ is decreased by X. As a result, the ignition timing in the next ignition cycle will be retarded by X. Next, in step 87, n is reset to zero and the process returns to the main routine. It is well known that knocking can be suppressed by retarding the ignition timing when it is detected that knocking has occurred.

FIG. 7 is a diagram for explaining the principle of the present invention, in which the horizontal axis represents the amplitude value of the knock sensor output, and the vertical axis represents the frequency of occurrence of the output of the amplitude value. In the figure, the frequency distribution of knock sensor output amplitude values when knocking does not occur is shown by a broken line b,
The frequency distribution of knock sensor output amplitude values when minute knocking (knocking to the extent that a human can hear the knocking sound after listening) is shown by the broken line c.
Further, the frequency distribution of knock sensor output amplitude values in engine conditions where minute knocking occurs is shown by a solid line d. Note that when large knocking occurs, the knock sensor output amplitude value also becomes large, so that its frequency distribution appears in the right margin of FIG. 7.

To obtain the background value, it is sufficient to obtain the average value ₀ of the knock sensor output amplitude values when no minute knocks occur as shown in Fig. 7, so b
The value of K is determined so that the value of K・₀ is at the position where the area where the frequency distribution of and the frequency distribution of c overlap each other is divided into two (the areas of e and f in the figure are equal). , if the knock sensor output amplitude value is smaller than K・₀ and the average value ₀ is updated every ignition cycle using that knock sensor output amplitude value, the updated value will be almost equal to ₀ in Fig. 7. be. That is, the processing in steps 80 and 81 in FIG. 6 corresponds to this. By performing such processing, the background signal can be detected during the knocking detection period.

As is clear from the above explanation, step 80 in FIG. 6 simultaneously performs both the processes of determining whether or not it is permissible to create a background signal and determining whether or not knocking has occurred. It is something.
However, in the present invention, the above-mentioned discrimination processing may be performed separately. FIG. 8 shows a case where this discrimination processing is performed separately. That is, in step 80a, it is determined whether or not knocking has occurred, and in step 80b, it is determined whether or not the process of step 81 for background value detection can be performed. In this way, if separate K' and K are used in steps 80a and 80b,
When detecting the occurrence of knocking (processing in step 80a), the degree of freedom in determining the threshold value is increased, which is very advantageous.

〔Effect of the invention〕

As explained in detail above, according to the present invention, the comparison reference value is the average value A that emphasizes the current knock sensor output and also takes advantage of past knock sensor outputs.
Since the judgment reference value is calculated based on, this judgment reference value can reduce the influence of noise etc.
It can track vibrations during transient periods, and there is no need to memorize multiple outputs from the knock sensor.
The capacity of the storage device also does not increase.

[Brief explanation of the drawing]

FIG. 1 is an overall schematic configuration diagram of an embodiment of the present invention, FIG. 2 is a block diagram of the control circuit of FIG. 1, and FIGS. 3 to 6 are flowcharts of each interrupt processing routine of the control circuit. FIG. 7 is a diagram for explaining the operation of the above embodiment, FIG. 8 is a flowchart of another embodiment of the interrupt processing routine of FIG. 6, and FIG. 9 is a block diagram showing the basic configuration of the present invention. 10... Cylinder block, 12... Knock sensor, 14... Distributor, 16, 18...
Crank angle sensor, 20... Control circuit, 36, 4
6...Input/output port, 48...Buffer and filter circuit, 50...Peak hold circuit, 54...
...A/D converter, 62...MPU, 64...
RAM, 66...ROM.

Claims (1)

[Scope of Claims] 1. A knock sensor (14) consisting of at least one vibration detection element that converts mechanical vibration into an amplitude fluctuation of an electric signal is attached to the engine body of an internal combustion engine, and a knock sensor (14) is installed in the engine body of an internal combustion engine, In a knocking detection device for an internal combustion engine that detects whether knocking has occurred, the peak value detection unit detects a peak value (a) of the amplitude value of the electrical signal in a predetermined crank angle range after ignition of at least one cylinder. and weighting the average value (A) of the peak values (a) so that the influence of recent peak values becomes stronger (for example, A=
(9・A+a)/10) and calculates the average value for each ignition, and the average value is used as a background value and is multiplied by a predetermined value (K, K'>1) to obtain a knock judgment reference value. (KA', KA), and a comparison means that compares the knock judgment reference value with the peak value, and determines whether or not knocking has occurred according to the comparison result. A knocking detection device for an internal combustion engine, characterized in that: