JPH0850157A - Resonance frequency measuring device - Google Patents

Abstract

PURPOSE:To facilitate the correction of resonance frequency of a band-pass filter, and improve the precision. CONSTITUTION:A standard signal (a) is inputted to a band-pass filter and a waveform shaping circuit 14 within a phase comparing circuit 12. The waveform shaping circuit 14 converts the standard signal (a) into a rectangular wave signal (b), and a phase comparator 17 outputs a pulse signal (d) having a pulse width corresponding to the phase difference between the rectangular wave signal (b) from the waveform shaping circuit 14 and the pass signal (c) outputted from the band-pass filter by the input of the standard signal (a). An integrating circuit 19 integrates the pulse signal (d) from the phase comparator 17, and outputs a DC signal (e) having a voltage corresponding to the pulse width of the pulse signal (d). Thus, when the frequency of the standard signal (a) is conformed to the resonance frequency of the band-pass filter, the frequency characteristic around the resonance frequency of the band-pass filter is converted into a voltage change having sharp curve characteristic on the basis that the phase of the standard signal (a) is equal to that of the pass signal (c).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonance frequency measuring device for precisely measuring the resonance frequency of a bandpass filter, and more particularly to the resonance frequency of a bandpass filter used as a part of a knock control system for automobiles. TECHNICAL FIELD The present invention relates to a resonance frequency measuring device that measures accurately.

[0002]

2. Description of the Related Art Generally, an automobile is provided with a knock sensor for detecting the occurrence of engine knocking.
A knock control system for preventing engine knocking based on a detection signal output from the knock sensor is mounted.

Here, FIG. 8 shows a knock control system mounted on an automobile. In FIG. 8, reference numeral 1 denotes a knock sensor. The knock sensor 1 is provided on an outer peripheral wall of a cylinder of an engine or the like. It is a sensor that detects vibration. That is, the knock sensor 1 converts the vibration acceleration when the engine is driven into an electric signal by utilizing the magnetostriction effect and the piezo effect of the high nickel alloy, and outputs a detection signal having a frequency corresponding to the vibration frequency of the engine. It is like this.

Reference numeral 2 denotes a control unit, and the control unit 2 includes a bandpass filter 3 and a processing circuit 4 (hereinafter referred to as "M
PU4 ”) is provided. The bandpass filter 3 is a filter that is configured by, for example, an electric circuit as shown in FIG. 9, and passes only the frequency when knocking occurs in the detection signal output from the knock sensor 1. That is, since the vibration frequency at the time of knocking occurrence is different depending on each engine, but is always a constant frequency (for example, 7 kHz), only the vibration frequency at the time of knocking occurrence out of the detection signal output from the knock sensor 1 is passed. As a result, the occurrence of knocking is transmitted to MPU4.

Further, the MPU 4 recognizes the occurrence of knocking by receiving a signal containing only the vibration frequency component at the time of knocking occurrence, and analyzes the strength of knocking. Further, the control unit 2 is connected to an ignition plug or the like (not shown) that ignites the fuel at a predetermined timing, and the MPU 4 delays the ignition timing of the ignition plug according to the strength of knocking. Control.

In the knock control system having such a structure, it is necessary to precisely set the resonance frequency of the bandpass filter 3 in order to accurately detect knocking of the engine.

Therefore, for example, when the control unit 2 of the knock control system is manufactured in a factory, an adjusting process is provided in the manufacturing process after the processes such as mounting and assembling the components of the control unit 2 are completed. In this adjustment process, the resonance frequency of the bandpass filter 3 is finally determined. That is, the bandpass filter 3 is provided with a resistance terminal (not shown) for finally determining the resonance frequency, and the resistance having an optimum resistance value for the resistance terminal is adjusted by the following adjustment work. The final determination of the resonance frequency is made by inserting 3A.

Here, the operation of adjusting the resonance frequency of the bandpass filter 3 will be described with reference to FIG.

First, the oscillator 5 is connected to the input terminal of the control unit 2, that is, the input terminal to which the knock sensor 1 is to be connected, and the bandpass filter 3 and the MPU are connected.
A monitor device 6 is connected between the monitor device 4 and the monitor device 4. Then, a reference signal having a predetermined frequency to be set by the oscillator 5 is input to the bandpass filter 3, and the monitor device 6 receives a pass signal output through the bandpass filter 3. Here, the monitor device 6 measures the voltage of the pass signal output from the band pass filter 3 and checks the resistance value of the resistor 3A to be inserted into the resistance terminal based on the voltage of the pass signal and the like.

Here, the frequency of the reference signal input to the bandpass filter 3 is changed, and the voltage change of the pass signal output from the bandpass filter 3 at this time is shown in the graph of FIG. That is, this is the frequency characteristic of the bandpass filter 3. As the frequency of the reference signal approaches the resonance frequency F0 of the bandpass filter 3, the voltage (amplitude) of the output signal increases, and the frequency of the input signal becomes the resonance frequency F0. Output signal voltage (amplitude) at the coincident point
Is the maximum.

Based on this characteristic, a point where the voltage (amplitude) of the passing signal is maximized is found by the monitor device 6, and the resistance value of the resistor 3A to be inserted into the resistor terminal is examined. Then, the resistor 3A having a resistance value based on the result is inserted into the resistor terminal, and the resonance frequency of the bandpass filter 3 is finally determined to be a predetermined frequency.

[0012]

However, the above-mentioned conventional technique has a problem that it is difficult to accurately and promptly determine the final resonant frequency of the bandpass filter 3.

That is, as shown in FIG. 11, the frequency characteristic of the bandpass filter 3 is a characteristic of drawing a gentle circular arc in the vicinity of the resonance frequency F0, and the degree of change of the passing signal in the vicinity of the resonance frequency is extremely small. For example, the voltage E0 at the resonance frequency F0 and Δf from the resonance frequency F0
Compared with the voltage E1 at the frequency F1 which is low by
The difference Δe between the voltage E0 and the voltage E1 has a very small value. Therefore, it is practically difficult to accurately determine the resonance frequency by measuring the voltage change of the passing signal.

As a result, the above-mentioned bandpass filter 3
In the adjustment work to finally determine the resonance frequency of
There is a problem that it is difficult to accurately and promptly find the point where the voltage (amplitude) of the passing signal is maximum by the monitor device 6 based on the frequency characteristic of the bandpass filter 3 shown in FIG.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a resonance frequency measuring device capable of accurately and quickly setting the resonance frequency of a bandpass filter.

[0016]

In order to solve the above-mentioned problems, the resonance frequency measuring means according to the invention of claim 1 uses an oscillator for inputting an AC reference signal to a bandpass filter, and a reference signal from the oscillator. Accordingly, there is adopted a configuration including resonance frequency detecting means for detecting the resonance frequency of the bandpass filter based on the phase difference between the pass signal output from the bandpass filter and the reference signal.

According to a second aspect of the present invention, the resonance frequency detecting means includes phase difference detecting means for outputting a pulse signal having a pulse width corresponding to a phase difference between the reference signal and the passing signal, and It is preferable that the pulse signal is composed of a signal converting means for converting the pulse signal into a DC signal having a voltage corresponding to the pulse width.

Further, as in the invention of claim 3, the signal converting means integrates the pulse signal output from the phase difference detecting means to thereby convert the pulse signal into a DC signal having a voltage corresponding to its pulse width. It is desirable to be composed of an integrating circuit for converting to.

[0019]

According to the first aspect of the present invention, when the frequency of the reference signal output from the oscillator to the bandpass filter approaches the resonance frequency of the bandpass filter, the bandpass filter outputs a pass signal. . When the frequency of the reference signal does not match the resonance frequency of the bandpass filter, a phase difference occurs between the reference signal and the pass signal. On the other hand, when the frequency of the reference signal matches the resonance frequency of the bandpass filter, the phases of the reference signal and the pass signal are the same. Further, the change in the phase difference between the reference signal and the passing signal is relatively large with respect to the change in the frequency of the reference signal. Therefore, the resonance frequency detecting means can accurately and quickly detect the resonance frequency of the bandpass filter based on the phase difference between the reference signal and the passing signal.

According to the second aspect of the invention, the phase difference detecting means outputs the pulse signal having the pulse width corresponding to the phase difference between the reference signal and the passing signal as described above, and the signal converting means. Outputs a DC signal having a voltage corresponding to this pulse signal. As a result, the voltage of the DC signal output from the signal converting means changes greatly even with a slight change in the frequency of the reference signal in the vicinity of the resonance frequency of the bandpass filter, and the voltage of the DC signal becomes maximum. That is, the resonance frequency of the bandpass filter can be found accurately and quickly.

According to the third aspect of the invention, the pulse width of the pulse signal output from the phase difference detecting means changes according to the phase difference between the reference signal and the passing signal. By integrating this pulse signal by the integrating circuit, it is possible to generate a DC signal whose voltage changes according to an increase or decrease in the pulse width of the pulse signal. This makes it possible to obtain a DC signal having a voltage corresponding to the pulse width of the pulse signal output from the phase difference detecting means.

[0022]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 7. In this embodiment, the resonance frequency of the bandpass filter 3 provided in the knock control system of the automobile shown in FIG. The setting will be described as an example.

In the figure, reference numeral 11 denotes an oscillator according to the present embodiment which is connected to an input terminal of the control unit 2, that is, an input terminal to which the knock sensor 1 is to be connected. The reference signal a is input. Here, the reference signal a is a sine wave signal set to the same frequency as the resonance frequency F0 to be set by the bandpass filter 3, as shown in FIG. 3 or 4. Further, the oscillator 11 is a bandpass filter 3
Of the phase comparison circuit 12 described later.
It is also connected to the input side of.

Reference numeral 12 denotes a phase comparison circuit as a resonance frequency detecting means. The phase comparison circuit 12 includes an oscillator 1
1 and the bandpass filter 3
Two signals, that is, the passing signal c output from the above are input. Here, the pass signal c is a signal that is output when the reference signal a passes through the bandpass filter 3, and the frequency of the reference signal a and the resonance frequency F0 of the bandpass filter 3 match, or Output when approximated. The output side of the phase comparison circuit 12 is connected to a monitor device 13 which is substantially the same as the monitor device 6 described in the prior art.

Here, the reference signal a and the passing signal c have the following characteristics with respect to their phases.

That is, when the frequency of the reference signal a and the resonance frequency F0 of the bandpass filter 3 match, the phases of the passing signal c and the reference signal a become equal, and the frequency of the reference signal a and the bandpass filter 3 are the same. When the resonance frequency F0 of 1 does not match, there is a characteristic that a phase difference occurs between the passing signal c and the reference signal a.

The phase comparison circuit 12 measures the resonance frequency of the bandpass filter 3 by utilizing the phase characteristics of the reference signal a and the passing signal c described above. Now, the circuit configuration of the phase comparison circuit 12 will be described in detail with reference to FIG.

In FIG. 2, reference numeral 14 designates a waveform shaping circuit, which is generally composed of a comparator 15.
The oscillator 1 is connected to the non-inverting input terminal of the comparator 15.
1 is connected and the reference signal a is input. The inverting input terminal of the comparator 15 is grounded, and the output terminal is the phase comparator 1 described later.
Connected to 7. Further, the output terminal of the comparator 15 is connected to a 5V DC power source via a pull-up resistor 16. Then, the waveform shaping circuit 14 converts the reference signal a into a square wave signal b, and the phase comparator 1
7 has the function of inputting.

Reference numeral 17 denotes a phase comparator 17 as a phase difference detecting means.
Is a one-chip IC including, for example, a logic circuit, and has at least two input terminals and one output terminal. As the phase comparator 17, for example, a one-chip IC manufactured by Motorola Co. having a product number MC14046B is used.

The output side of the waveform shaping circuit 14 is connected to one of the input terminals of the phase comparator 17 to input the square wave signal b. The other input terminal is connected to the output side of the bandpass filter 3 via the capacitor 18, and the pass signal c from the bandpass filter 3 is input. Further, the output terminal of the phase comparator 17 is connected to an integrating circuit 19 described later. Then, the phase comparator 17 outputs the square wave signal b and the passing signal c.
Pulse signal d having a pulse width W corresponding to the phase difference between
Is output. The pulse width W is, as shown in FIG.
It is between the fall and rise of the pulse signal d.

Reference numeral 19 denotes an integrating circuit as a signal converting means, and the integrating circuit 19 is composed of two resistors 2 connected in series.
0,21 and two capacitors 22 connected in parallel,
23 and a buffer 24 arranged on the output side. The output side of the phase comparator 17 is connected to the input side of the integration circuit 19, and the output side of the integration circuit (the output terminal of the buffer 24) is connected to the monitor device 1.
Connected to 3. Then, the integrating circuit 19 outputs the pulse signal d output from the phase comparator 17.
Is integrated and converted into a DC signal e having a voltage corresponding to the pulse width W of the pulse signal d.

The resonance frequency measuring apparatus according to the present embodiment has the above-mentioned structure, and its operation will be described below with reference to FIGS. 3 to 5.

First, a reference signal a is output from the oscillator 11, and the reference signal a is input to the bandpass filter 3 and the waveform shaping circuit 14 of the phase comparison circuit 12.

Then, in the waveform shaping circuit 14, when the reference signal a is input to the comparator 15, the comparator 15 compares the potential of the reference signal a with the ground potential (for example, 0V), and the potential of the reference signal a. Is higher than the ground potential, a signal of 5 V is output, and when it is lower than the ground potential, a signal of −5 V is output, and as a result, a square wave signal b is generated. In this way, the reference signal a is converted into the square wave signal b because the voltage (amplitude) of the reference signal a is small, and therefore the reference signal a is input to the phase comparator 17 as it is. This is because the processing may not be performed reliably.

On the other hand, since the reference signal a is input from the oscillator 11 to the bandpass filter 3, the bandpass filter 3 outputs the pass signal c.

Then, the phase comparator 17 has
The square wave signal b from the waveform shaping circuit 14 and the pass signal c from the band pass filter 3 are input respectively.
Then, the phase comparator 17 outputs a pulse signal d having a pulse width W corresponding to the phase difference between the square wave signal b and the passing signal c. That is, the phase comparator 17 generates the pulse signal d having the pulse width W corresponding to the time from the rising of the square wave signal b to the rising of the passing signal c.

Here, as described above, when the frequency of the reference signal a and the resonance frequency F0 of the bandpass filter 3 match, the phases of the passing signal c and the reference signal a become equal, and the frequency of the reference signal a. And the resonance frequency F0 of the bandpass filter 3 do not match, there is a characteristic that a phase difference occurs between the passing signal c and the reference signal a.

Due to such phase characteristics, when the reference signal a and the resonance frequency F0 of the bandpass filter 3 match, the phases of the reference signal a (square wave signal b) and the passing signal c are as shown in FIG. Since they are equal, the pulse width W of the pulse signal d becomes zero, and the pulse signal d is output as a substantially DC signal.

On the other hand, the reference signal a and the bandpass filter 3
When the resonance frequency F0 of is close but does not match,
As shown in FIG. 4, since a phase difference occurs between the passing signal c and the reference signal a, a pulse signal d ′ having a pulse width W is obtained.
Is output. Then, if the phase difference between the passing signal c and the reference signal a is large, the pulse width W of the pulse signal d'is correspondingly wide, and if the phase difference between the passing signal c and the reference signal a is small, it corresponds to it. As a result, the pulse width W of the pulse signal d'is narrowed.

Then, the pulse signal d output from the phase comparator 17 is input to the integrating circuit 19. The integrating circuit 19 integrates the pulse signal d by the first CR integrating circuit including the resistor 20 and the capacitor 22 and the second CR integrating circuit including the resistor 21 and the capacitor 23,
The DC signal e is output via the buffer 24. That is, as shown in FIG. 3, when the pulse width W of the pulse signal d is zero, the integrator circuit 19 outputs the DC signal e having a maximum voltage of, for example, 5V. On the other hand, as shown in FIG. 4, when the pulse signal d'has a pulse width W, the integrating circuit 19 outputs the DC signal e'having a voltage lower than the maximum voltage 5V. That is,
The DC signal e output from the integrating circuit 19 has a maximum voltage when the pulse width W of the pulse signal d is zero, and the voltage decreases as the pulse width W of the pulse signal d increases. Then, the DC signal e output from the integrating circuit 19 is input to the monitor device 13.

As described above, finally the phase comparison circuit 12
The voltage of the DC signal e output from the integrating circuit 19 changes according to the phase difference between the reference signal a and the passing signal c.
The phase difference between the reference signal a and the passing signal c is the frequency of the reference signal a and the resonance frequency F0 of the bandpass filter 3.
As a result, the voltage of the DC signal e changes corresponding to the frequency difference between the frequency of the reference signal a and the resonance frequency F0 of the bandpass filter 3.

FIG. 5 shows the voltage change of the DC signal e when the frequency of the reference signal a is changed near the resonance frequency F0 of the bandpass filter 3. According to this, as for the voltage of the DC signal e, the frequency of the reference signal a is the resonance frequency F0.
It can be seen that the voltage becomes maximum at the time of, and the voltage change around the resonance frequency F0 is sharp. For example,
When the voltage E0 at the resonance frequency F0 and the voltage E1 at the frequency F1 lower by .DELTA.f than the resonance frequency F0 are compared, a large difference .DELTA.e between the voltage E0 and the voltage E1 appears. Then, this Δe becomes a very large value as compared with the characteristic Δe shown in FIG.

Further, here, the resonance frequency F of the bandpass filter 3 is measured by using the resonance frequency measuring apparatus according to the present embodiment.
The voltage change of the DC voltage e near 0 will be described based on the actual test results.

FIG. 6 shows the conventional circuit configuration of FIG. 10 (hereinafter referred to as “conventional circuit”), in which the frequency of the reference signal input to the bandpass filter 3 is changed in the vicinity of the resonance frequency of the bandpass filter 3. The voltage change of the pass signal output from the band pass filter 3 at that time is shown in the graph. On the other hand, FIG. 7 shows the circuit configuration of FIG. 1 according to the present embodiment (hereinafter, referred to as “embodiment circuit”).
, The frequency of the reference signal input to the bandpass filter 3 is changed in the vicinity of the resonance frequency of the bandpass filter 3, and the pass signal output from the bandpass filter 3 at that time is input to the phase comparison circuit 12. 3 is a graph showing the voltage change of the DC signal output from the phase comparison circuit 12. The resonance frequency of the bandpass filter 3 used in this test is 14.4 kHz,
The allowable range of the resonance frequency error of the bandpass filter 3 is 14.3 to 14.5 kHz.

Further, according to the result of the conventional circuit shown in FIG. 6, the voltage change of the passing signal in the allowable range of the frequency error is only 5 mV, whereas according to the result of the embodiment circuit shown in FIG. The voltage change of the DC signal in the allowable range of the frequency error is 160 mV. From this result, it can be seen that in the present embodiment, the frequency characteristic near the resonance frequency of the bandpass filter 3 can be converted into a large voltage change.

Thus, according to this embodiment, only when the frequency of the reference signal a input to the bandpass filter 3 and the resonance frequency F0 of the bandpass filter 3 match.
Paying attention to the fact that the pass signal c output from the band pass filter 3 and the reference signal a have the same phase, the phase comparison circuit 12 causes the DC signal e having a voltage corresponding to the phase difference between the reference signal a and the pass signal c. The frequency characteristic of the bandpass filter 3 near the resonance frequency can be converted into a large voltage change of the DC signal e, and the resonance frequency F0 of the bandpass filter 3 can be measured accurately and quickly. it can.

Therefore, in the adjustment work for finally determining the resonance frequency F0 of the bandpass filter 3, if the resonance frequency measuring apparatus according to this embodiment is used, the point where the voltage of the DC signal e becomes maximum can be easily grasped. Therefore, the resistance value of the resistor 3A to be inserted in the resistance terminal can be accurately checked. Therefore, the resonance frequency F0 of the bandpass filter 3 can be set precisely, the performance of the bandpass filter 3 can be improved, and the efficiency of the adjustment work can be greatly increased.

In the above embodiment, the phase comparator 17 outputs the pulse signal d having the pulse width W from the falling edge to the rising edge of the pulse signal d, but the present invention is not limited to this. Alternatively, a pulse signal whose pulse width from the rising edge to the falling edge of the pulse signal corresponds to the phase difference between the reference signal a (square wave signal b) and the passing signal c may be output.

In the above embodiment, the bandpass filter 3 provided in the knock control system of the automobile is used.
However, the present invention is not limited to this, and can be applied to the measurement and setting of the resonance frequency of various band pass filters used for other purposes.

[0050]

As described above in detail, according to the first aspect of the invention, based on the phase difference between the reference signal input to the bandpass filter by the oscillator and the pass signal output from the bandpass filter accordingly. Since the resonance frequency of the bandpass filter is detected, the resonance frequency of the bandpass filter can be measured accurately and quickly.
That is, when the frequency of the reference signal matches the resonance frequency of the bandpass filter, the phases of the reference signal and the passing signal become equal to each other. Since the resonance frequency is obtained, the resonance frequency of the bandpass filter can be accurately measured.

Thus, for example, when shipping the bandpass filter, inspection and adjustment work for correcting variations in the resonance frequency of the bandpass filter can be facilitated, and the resonance of the bandpass filter can be facilitated. The frequency can be set precisely.

According to a second aspect of the present invention, the resonance frequency detecting means includes phase difference detecting means for outputting a pulse signal having a pulse width corresponding to the phase difference between the reference signal and the passing signal. Since the pulse signal is composed of the signal converting means for converting the pulse signal into the DC signal having the voltage corresponding to the pulse width, the increase / decrease in the phase difference between the reference signal and the passing signal is finally converted into the increase / decrease in the voltage of the DC signal. be able to. Thereby, even when the frequency of the reference signal is changed in the vicinity of the resonance frequency of the bandpass filter, the voltage of the DC signal can be greatly changed. Therefore, the resonance frequency of the bandpass filter can be accurately and quickly measured based on the voltage of the DC signal.

Further, according to the invention of claim 3, the pulse output from the phase difference detecting means is integrated to convert the pulse signal into a DC signal having a voltage corresponding to the pulse width thereof. An increase / decrease in the phase difference between the reference signal and the passing signal can be converted into an increase / decrease in the voltage of the DC signal, and the resonance frequency of the bandpass filter can be easily measured.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a state in which a resonance frequency measuring device according to an embodiment of the present invention is connected to a knock control system.

FIG. 2 is an electric circuit diagram showing a phase comparison circuit of the resonance frequency measuring device.

FIG. 3 is a waveform diagram showing characteristics of each signal when the frequency of the reference signal and the resonance frequency of the bandpass filter match.

FIG. 4 is a waveform diagram showing characteristics of each signal when the frequency of the reference signal and the resonance frequency of the bandpass filter do not match.

FIG. 5 is a characteristic diagram showing a voltage change of a DC signal output from the phase comparison circuit.

6 is a characteristic diagram showing frequency characteristics of a bandpass filter having the conventional circuit configuration shown in FIG.

7 is a characteristic diagram showing the result of converting the frequency characteristic of the bandpass filter by the circuit configuration according to the present embodiment shown in FIG.

FIG. 8 is a block circuit diagram showing a knock control system according to a conventional technique.

FIG. 9 is a circuit diagram showing a bandpass filter.

FIG. 10 is a block circuit diagram showing a state in which an oscillator and a monitor device are connected to the knock control system.

FIG. 11 is a characteristic diagram showing frequency characteristics of a bandpass filter according to a conventional technique.

[Explanation of symbols]

 11 Oscillator 12 Phase Comparison Circuit (Resonance Frequency Detection Means) 13 Monitor Device 17 Phase Comparator (Phase Difference Detection Means) 19 Integration Circuit (Signal Conversion Means)

Claims (3)

[Claims] 1. An oscillator for inputting an AC reference signal to a bandpass filter, and the band based on a phase difference between a pass signal output from a bandpass filter according to the reference signal from the oscillator and the reference signal. A resonance frequency measuring device comprising a resonance frequency detecting means for detecting the resonance frequency of a pass filter. 2. The resonance frequency detection means outputs a pulse signal having a pulse width corresponding to the phase difference between the reference signal and the passing signal, and the pulse signal corresponds to the pulse width. 2. The resonance frequency measuring device according to claim 1, comprising a signal converting means for converting the voltage into a DC signal. 3. The signal converting means comprises an integrating circuit for converting the pulse signal output from the phase difference detecting means into a direct current signal having a voltage corresponding to its pulse width. The resonance frequency measuring device according to claim 2, wherein