JPH09329487A - Acceleration sensor - Google Patents

Abstract

(57) An object of the present invention is to provide an acceleration sensor which can achieve both suppression of sharpness and increase of sensitivity and which has a simple structure. A detection output of a piezoelectric conversion element 1 is input to a servo circuit 14. The servo circuit 14 advances the phase of the output signal of the piezoelectric conversion element 1 between 20 and 90 degrees,
And the frequency transfer characteristic z is z = a + jb (where 0 <
The control voltage generating circuit 3 has a <1 and 0 <b <2), and the impedance 2 receives the output of the control voltage generating circuit 3. Further, the control voltage generation circuit 3
Temperature compensation can be performed by using a temperature compensating element such as a thermistor for at least one of the internal resistance and the impedance 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor, and more particularly to an acceleration sensor which is compatible with both improvement of sensitivity and suppression of sharpness and which is suitable for detecting engine knock vibration and the like.

[0002]

2. Description of the Related Art A resonance type acceleration sensor, which is one of acceleration sensors for detecting engine knock vibration and the like, detects an acceleration component having a specific frequency component. What was used has been put to practical use. As is well known, the knock sensor detects knock vibration peculiar to the engine, and it is necessary to detect the knock vibration with high sensitivity even if the natural vibration of the engine varies.

One of conventional sensors of this type is disclosed in, for example, Japanese Patent Publication No. 2-1248. This sensor, as shown in FIG. 12, has a C ₀ R between the output end 21a of the piezoelectric conversion element 21 and the ground.
It is configured by connecting a resistor 22 having a resistance value R satisfying ω = 0.5 to 2. Here, C ₀ is the capacitance of the piezoelectric conversion element 21, and ω is the resonance angular frequency. As described above, according to the knock sensor in which the resistance 22 is connected in parallel to the piezoelectric conversion element 21, as compared with the knock sensor without the resistance 22,
The sensitivity, that is, the output voltage per unit acceleration decreases. This conventional knock sensor suppresses the sharpness of its frequency characteristic near the resonance frequency by sacrificing the sensitivity.

[0004]

However, the sharpness of the above-described conventional knock sensor can be suppressed to about 1/2 at most as compared with the one without the resistor 22, and the engine knock frequency is manufactured. There is a problem that it is not possible to have a substantially uniform sensitivity to variations. Further, in the conventional technology, the suppression of the sharpness of the knock sensor and the increase of the sensitivity cannot be achieved at the same time, and if the suppression of the sharpness of the knock sensor is increased, the sensitivity is greatly reduced accordingly. there were.

An object of the present invention is to eliminate the above-mentioned problems of the prior art, and to provide an acceleration sensor having a simple structure which can achieve both suppression of sharpness and increase in sensitivity. . Another object of the present invention is to provide an acceleration sensor that can suppress the sharpness of the conventional device to a greater degree and can provide substantially uniform sensitivity to manufacturing variations in engine knock frequency.

[0006]

In order to achieve the above-mentioned object, the present invention provides an acceleration sensor using a piezoelectric conversion element, in which an output signal of the piezoelectric conversion element is 20 to 9.
The phase is advanced between 0 degrees, and the frequency transfer characteristic z is z
= A + jb (where 0 <a <1, 0 <b <2) is provided, and the output of the control voltage generation circuit is connected to the output end of the piezoelectric conversion element via an impedance. The feature is that it is done. According to the present invention, the velocity proportional component, which is output from the control voltage generating circuit and is 90 degrees out of phase with the detected voltage V of the piezoelectric conversion element, and the in-phase displacement proportional component, are output via the impedance. Applied to the piezoelectric conversion element. The velocity proportional component exerts an inverse piezoelectric effect on the piezoelectric conversion element and increases the vibration damping force on the piezoelectric conversion element. Therefore, the sharpness is lowered. On the other hand, the displacement proportional component is superimposed on the detection voltage of the piezoelectric conversion element to increase the sensitivity (gain). As a result, the sharpness can be suppressed and the sensitivity can be increased at the same time.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. First, a schematic configuration of an embodiment of the present invention will be described with reference to FIG. In the figure, 11 is an engine of an automobile or the like, 12 is a knock sensor for detecting knocking of the engine, and 13 is an electronic control unit (ECU). The ECU 13 includes a servo circuit 14 mounted according to the present invention and a waveform processing circuit 15 for waveform-processing a detection signal.
And a microcomputer 16 for determining knocking by the output of the waveform processing circuit 15.

Next, the configuration and operation of this embodiment will be described more specifically with reference to FIG. In the figure, 1 is a piezoelectric conversion element, 2 is an impedance having a resistance value R, 3 is a control voltage generation circuit which is connected in parallel with the impedance 2, and which servo-controls the piezoelectric conversion element 4, and 4 is a sensor output terminal. Reference numeral 5 is a control voltage feedback terminal. The impedance 2, the control voltage generation circuit 3, and the control voltage feedback terminal 5 form the servo circuit 14. It is assumed that the imaginary part of the impedance 2 is so small that it can be ignored.

The operation of this embodiment will be described below based on the piezoelectric theory. When the piezoelectric conversion element 1 of the knock sensor receives the vibration acceleration α, the displacement w of the piezoelectric conversion element 1 is given by the following (1), where velocity is dw / dt and acceleration is d ² w / dt ^2. ) Can be represented by a formula.

Md ² w / dt ² + cdw / dt + kw = mα−β 0 V (1) where m is the mass of the piezoelectric conversion element 1, c is mechanical damping, k is rigidity, and V is output voltage. , Also generally β0
> 0. -Β 0 V indicates that a negative force is generated due to the inverse piezoelectric effect.

Next, the output voltage V is
When β1 is a positive coefficient, Co is a sensor capacitance, and Vcon is a control voltage at the control voltage feedback terminal 5, it can be expressed by the following equation (2).

[0012]

[Equation 1] Now, assuming that the piezoelectric conversion element 1 oscillates at an angular frequency ω, the equations (1) and (2) are expressed by the following equations (3) and (4) using the complex amplitude ( ^* ). be able to.

{(K−mω ² ) + jωc} w ^* = mα−β0 V ^* (3) V ^* (1 + 1 / jCo Rω) = β1 w ^* + V ^* con / jCo Rω (4) where the angle is When the voltage transfer function of the control voltage generation circuit 3 at the frequency ω is a + jb, the following equation (5) is established. V ^* con = (a + jb) V ^* (5) If V ^* con and V ^* are deleted from the equations (3), (4) and (5), the sensor amplitude w expressed by the following equation (6) is obtained. You can get the formula of ^* .

[0014]

[Equation 2]

At the resonance angular frequency, the real part of the equation (6) disappears, so the following equation (7) is established.

[0016]

(Equation 3) From the equation (7), the sharpness Q is given by the following equation (8).

[0017]

(Equation 4) Further, the sensitivity (gain) V ^* can be obtained from the equations (3), (4), (5) and (7), and is represented by the following equation (9).

[0018]

(Equation 5) In the equations (8) and (9), a is plotted on the abscissa and b is plotted on the ordinate, which are shown in FIGS. 3 (a) and 3 (b), respectively. However, as an example of specifications, ωc = 0.5β0
β1, Co Rω = 1, α = 1G, β1 m / ωc = 0.5
It was VOLT / G. In equations (8) and (9), a =
When b = 0, the control voltage generating circuit 3 is not provided and has the same characteristics as the device disclosed in Japanese Patent Publication No. 2-1248 described in the prior art. Therefore, the sharpness of this conventional device is Q = 35 at the origin of FIG. 3 (a), and its sensitivity (gain) is V ^* = 180 mV at the origin of FIG. 3 (b). .

However, in this embodiment, since the servo mechanism including the control voltage generating circuit 3 is provided, as is apparent from FIG. 3A, the sharpness Q is within the range of a <1 and b> 0. Is 25 or 15 smaller than the conventional 35
Etc., and can be suppressed to a greater degree than the conventional sharpness. Also, according to this embodiment, FIG.
As is clear from the above, the sensitivity (gain) in the range of a <1 and b> 0 can be set to, for example, 300 mV, which is much higher than the gain of 180 mV of the conventional device.
From the above, in the present embodiment, the control voltage generation circuit 3
Since a servo mechanism consisting of
An acceleration sensor with low sharpness and high sensitivity can be obtained. As is apparent from the drawing, it is preferable that the sharpness Q is 25 or less and the sensitivity (gain) is 220 mV or more,
Particularly, sharpness Q is 15 or less, sensitivity (gain) is 300 mV
The above is better.

Now, the real part a of the control voltage transfer function
And the imaginary part b generally changes in frequency. Especially,
The suitable existence range of the real part a and the imaginary part b at frequencies near the resonance frequency, that is, the common region of the suitability ranges of FIGS. It is understood that the phase may be advanced by 20 to 90 degrees so that the real part a is 0 to 1 and the imaginary part b is 0 to 2.

Next, FIG. 5 shows a specific example of the control voltage generation circuit 3 which satisfies the condition of FIG. The control voltage generating circuit 3 is composed of a high-pass filter that advances the phase and is composed of a capacitor C1, a resistor R1, a voltage follower and a DC blocking capacitor C2. Now, as shown in the figure, if the input voltage of the control voltage generation circuit 3 is Vi, the output voltage of the voltage follower is Vo, and the single power supply voltage Vcc of the operational amplifier, the following equation holds.

(Vo-Vcc / 2) / (Vi-Vcc / 2) = jωC1R1 / (1 + jωC1R1) = (ωC1R1) ² / {1+ (ωC1R1) ² } + j × ωC1R1 / {1+ (ωC1 R1) ² } = a + jb (10) Therefore, in this specific example, it becomes as follows. a = (ωC1 R1) ² / {1+ (ωC1 R1) ² } b = ωC1 R1 / {1+ (ωC1 R1) ² } Further, the above equation (10) is expressed in Nyquist diagram as shown in FIG. 7. . The horizontal axis of FIG. 7 is (Vo −Vcc / 2) / (Vi
-Vcc / 2) represents the real number component, that is, a, and the vertical axis represents the imaginary number component, that is, b. The phase advance angle θ is θ = tan ⁻¹ b /
a, b, that is, frequencies ω, C1, R
By designing 1 appropriately, the phase advance angle θ is 20 to
It can be 90 degrees.

For example, the angular frequency ω = 2π × 12000 =
At 75398 rad / sec (frequency = 2 kHz), R
When 1 = 1100Ω and C1 = about 6.8 nF, the phase advance angle θ becomes about 60 degrees (A1 point in FIG. 7), and R1 =
When 11 KΩ and C1 = about 1.2 nF, the phase advance angle θ becomes about 45 degrees (point A2 in FIG. 7), and an acceleration sensor with low sharpness and high sensitivity can be obtained. Here, if C2 has a relatively large capacitance of 0.1 μF or more, there is not much resistance to alternating current.

In this circuit, if at least one of the resistor R1 and the impedance 2 is a thermistor, temperature compensation can be performed and the performance of the acceleration sensor can be further improved.

Next, another specific example of the control voltage generating circuit 3 is shown in FIG. The control voltage generation circuit 3 of FIG. 6 is an all-pass filter characterized by shifting the phase, and as shown in the figure, a DC blocking of a capacitor C, three resistors R, an operational amplifier, a capacitor having a relatively large capacity, etc. It is composed of a resistor C2. In this circuit, when the input voltage is Vi and the output voltage is Vo, the following equation is established.

(Vo −Vcc / 2) / (Vi −Vcc / 2) = − (1-jωCR) / (1 + jωCR) = − (1-jωCR) ² / {1+ (ωCR) ² } = [{(ωCR ) ² −1} + j2ωCR] / {1+ (ωCR) ² } = a + jb (11) Therefore, in this specific example, the values of a and b are as follows. a = {(ωCR) ² −1} / {1+ (ωCR) ² } b = 2ωCR / {1+ (ωCR) ² } Further, the Nyquist diagram of the equation (11) is as shown in FIG. . The horizontal axis of FIG. 8 is (Vo-Vcc / 2) / (Vi
-Vcc / 2) represents the real number component, that is, a, and the vertical axis represents the imaginary number component, that is, b. The phase advance angle θ is θ = tan ⁻¹ b /
a, b, that is, frequencies ω, C1, R
By designing 1 appropriately, the phase advance angle θ is 20 to
It can be 90 degrees.

For example, angular frequency ω = 75398 rad / sec
At (frequency = 12 kHz), R1 = 47 KΩ, C
= About 270 PF, the phase advance angle θ is about 90 degrees (see FIG. 8).
A1 point), and R = 47KΩ, C = approximately 470
If PF, the phase advance angle θ is about 60 degrees (A2 point in Fig. 8)
Therefore, it is possible to obtain an acceleration sensor with low sharpness and high sensitivity. Here, if C2 has a relatively large capacitance of 0.1 μF or more, there is not much resistance to alternating current.

If at least one of the three resistors R and the impedance 2 is formed of a thermistor, temperature compensation can be performed and the performance of the acceleration sensor can be further improved.

Now, the definition of the sharpness will be described. The sharpness indicates the sharpness of the resonance curve.
As shown in (1), the ratio between the resonance frequency f0 and the frequency width Δf at 1/2 ^{1/2 of} the maximum gain, that is, the value represented by the sharpness Q = f0 / Δf.

Next, the operation of the configuration shown in FIG. 2 will be qualitatively described with reference to FIG. The detection voltage V of the piezoelectric conversion element 1 generated at the terminal 4 is input to the control voltage generation circuit 3. As described above, the control voltage generation circuit 3 outputs the signal Vcon having a different amplitude and a phase θ advanced by 20 to 90 degrees. Now, assuming that V = sin ωt, the signal Vcon becomes as follows.

Vcon = sin (ωt + θ) = cos θsin ωt
+ Sin θcos ωt From this equation, the signal Vcon is a sin ωt component which is a component in phase with the detection voltage V, that is, the displacement proportional component Vcon1 and Vcon.
It can be seen that is a combination of the cos ωt component, which is a component deviated by 90 degrees, that is, the velocity proportional component Vcon2. And
This signal Vcon is applied to the piezoelectric conversion element 1 which is a sensor via the impedance 2. The velocity proportional component V
Since con2 is a component deviated from the output voltage V of the piezoelectric conversion element 1 by 90 degrees, a velocity proportional force is generated by the inverse piezoelectric effect. Since the vibration damping force is originally a velocity proportional force, the inverse piezoelectric effect increases the vibration damping force, and thus the sharpness is reduced. As described above, in the configuration of FIG. 2, since the inverse piezoelectric effect is positively utilized, the sharpness can be significantly suppressed. It is obvious that the inverse piezoelectric effect corresponds to −β0V in the equation (1). Further, since the displacement proportional component Vcon1 is in phase with the detection voltage V, it is superimposed on the detection voltage V, and the sensitivity (gain) is increased.

[0032]

As is apparent from the above description, in the present invention, the output signal of the piezoelectric conversion element is advanced in phase between 20 and 90 degrees, and the frequency transfer characteristic z is z = a + jb.
(Provided that 0 <a <1, 0 <b <2) is provided, and the output of the control voltage generation circuit is connected to the output end of the piezoelectric conversion element via the impedance. Therefore, the sharpness can be suppressed and the sensitivity can be increased at the same time. The frequency characteristics a and b of the device of the present invention and the conventional device are shown in FIG. 11, and it can be seen that the present invention has a higher sharpness and higher sensitivity than the conventional device. Further, the sensitivity range d1 according to the present invention is wider than the sensitivity range d2 of the conventional device, and it is possible to provide a substantially uniform high sensitivity with respect to manufacturing variation of the engine knock frequency. Further, if temperature compensation is performed using a temperature compensating element such as a thermistor for at least one of the resistance and the impedance in the control voltage generating circuit, a higher performance acceleration sensor that is not affected by temperature can be provided. Like

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of the present invention.

FIG. 2 is a circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 3 is a diagram showing sharpness and sensitivity (gain) obtained by the present invention.

4 is a frequency transfer characteristic a of the control voltage generation circuit of FIG.
It is a figure which shows the suitable existence area of a and b of + jb.

5 is a circuit diagram showing a specific example of the control voltage generation circuit of FIG.

FIG. 6 is a circuit diagram showing another specific example of the control voltage generation circuit of FIG.

FIG. 7 is a Nyquist diagram for the circuit of FIG.

FIG. 8 is a Nyquist diagram for the circuit of FIG.

FIG. 9 is a diagram for explaining the definition of sharpness.

FIG. 10 is a characteristic diagram qualitatively explaining the operation of the present invention.

FIG. 11 is a diagram illustrating an effect of the present invention.

FIG. 12 is a configuration diagram of a conventional device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric conversion element, 2 ... Impedance, 3 ... Control voltage generation circuit, 4 ... Sensor output terminal, 5 ... Control voltage feedback terminal, 11 ... Engine, 12 ... Knock sensor, 13 ... Electronic control unit (ECU), 14 ... Servo circuit, 15 ... Waveform processing circuit, 16 ... Microcomputer.

Claims (2)

[Claims] 1. An acceleration sensor using a piezoelectric conversion element, wherein an output signal of the piezoelectric conversion element is phase advanced between 20 and 90 degrees, and a frequency transfer characteristic z is z = a + jb.
(Provided that 0 <a <1, 0 <b <2) is provided, and the output of the control voltage generation circuit is
An acceleration sensor characterized in that it is connected to an output end of the piezoelectric conversion element. 2. The acceleration sensor according to claim 1, wherein a temperature compensation element such as a thermistor is used for at least one of the resistance and the impedance in the control voltage generation circuit to perform temperature compensation. Acceleration sensor.