JPH02171659A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To achieve a better performance with a thermal balance by a method wherein a plurality of piezo-electric elements are provided and grasped between a weight and a metal rigid body to be made non-continuous to a conductive case concurrently serving as shield. CONSTITUTION:A metal rigid body 30 is made to abut the undersurface of an insulation plate 9 and a weight 2, piezopelectric elements 4a and 4b and the insulating plate 9 are pierced by a fixing screw 5 and screwed down together with the rigid body 30. The elements 4a and 4b are connected in parallel to generate a voltage according to an acceleration with the weight 2. Signals of the elements 4a and 4b are amplified by a charge amplifier 6 and an earth circuit of the amplifier 6 is connected to a conductive case 1. With such an arrangement, the elements 4a and 4b are kept from being earthed with the insulation plate 9 so that the conductive case 1 is at an earth potential and brings out a shielding effect. With a screw 5 and a fixing nut 15 as fixing means, the rigid body 30 and the weight 2 are balanced thermally, thereby producing a sensor with a better performance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an acceleration sensor using a piezoelectric element for detecting vibration and riding comfort for automobiles.

[Prior Art] Piezoelectric sensors are used to detect vibrations and ride comfort in automobiles.
For example, Ceras wood, series No. 5 ceramic sensor 73. Nα32, published by Nilesera Publishing, P81-85
Described in "Force and Acceleration Sensor (1)".

Acceleration sensors using such piezoelectric sensors, weights, and charge amplifiers are applied, for example, to electronically controlled suspensions that control the ride comfort of automobiles.

When piezoelectric sensors are applied to electronically controlled suspensions,
The problem is how to solve the problem of high impedance and capacitance of this piezoelectric sensor, which makes it susceptible to external noise.

For this reason, conventional impedance conversion circuits are built-in,
Efforts have been made such as grounding one side of the electrode of the piezoelectric sensor to the case so that the case has a shielding effect.

[Problem to be solved by the invention]

However, in this case, when used in situations such as automobiles, where a single battery power source is used and the body of the automobile is grounded, if one electrode of the piezoelectric sensor is placed in a case, the acceleration The detection signal varies around ground, whereas the amplifier, for example,
Since the amplification is performed centering on the divided points, it is difficult to separate the detected signal from the fluctuations in the power supply voltage, which has the disadvantage of disrupting the signal and making it more susceptible to power supply voltage fluctuations and noise.

To deal with this, a solution is to use a charge amplifier instead of an impedance conversion circuit, but charge amplifiers have practical problems even in general use of dual-type sources, and technically there are It was difficult.

Furthermore, there was a problem in the circuit configuration for configuring the charge amplifier using a single power supply and being resistant to fluctuations in the power supply voltage.

In addition, in order to optimally configure the charge amplifier, it is necessary to keep both electrodes of the piezoelectric sensor above ground potential, and if the case is grounded, how should they be insulated from the case? The problem is how to fix the piezoelectric sensor to the case.

Furthermore, when using an accelerometer that uses a piezoelectric sensor and a weight for automobiles, in order to extract only acceleration stably against changes in environmental temperature, it is necessary to It is necessary to remove the so-called pyroelectricity by some means.

Furthermore, when using a piezoelectric sensor mounted on a vehicle, it is necessary to eliminate the influence of unnecessary signals such as unsprung vibration of the vehicle body, engine vibration, and resonance frequency of the mounting structure of the piezoelectric sensor itself.

This invention was made to solve the above-mentioned problems.It is resistant to fluctuations in power supply voltage, operates on a single N source voltage, is resistant to noise, has a wide temperature range for replacement, and can withstand severe temperature changes. The aim is to obtain an acceleration sensor that is optimal for use under unnecessary external vibrations.

[Means for Solving the Problems] An acceleration sensor according to the present invention includes a plurality of piezoelectric elements that are attached together with a metal weight to a conductive case via an insulating plate and output detection signals according to acceleration, and the piezoelectric elements. A charge amplifier that amplifies the output signal of and connects a conductive case and a ground circuit, a rigid metal body that supports the weight and the piezoelectric element and is non-conductively fixed to the conductive case with an insulating plate, and this rigid metal body and the weight. and fixing means for thermally balancing and mechanically joining the two.

[For production]

The piezoelectric element in this invention is floated from the ground potential by an insulating plate, has a conductive outer ground at ground potential to provide a shielding effect, and is thermally balanced with a rigid metal body by a fixing means to prevent pyroelectricity caused by temperature changes. It acts to soften the influence and suppress the influence of noise by extracting a detection signal corresponding to acceleration from the piezoelectric element and amplifying it with a charge amplifier.

〔Example〕

Embodiments of the acceleration sensor of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram showing the configuration of one embodiment. In this FIG. 1, l is a conductive case.

Piezoelectric elements 4a, 4b and weight 2 are placed at predetermined locations on this conductive case l via insulation vi9, and electrodes 3a are provided on the upper surface of piezoelectric element 4a and the lower surface of piezoelectric element 4b, respectively. Electrodes 3b are also provided on the lower surface of piezoelectric element 4a and on the upper surface of piezoelectric element 4b.

An epoxy board or a ceramic board such as a ceramic board is used as the insulation vi9, and a rigid metal body 30 is brought into contact with the lower surface of the insulation board 9.

Along with this metal rigid body 30, the weight 2, the piezoelectric element 4a,
4b and the insulating plate 9, and is screwed onto the fixing screw 5 with a nut 15 on the lower surface side of the metal rigid body 30.

Thus, piezoelectric elements 4a, 4b are electrodes 3a.

3b and connected in parallel, these piezoelectric elements 4a, 4
A detection unit composed of a metal body 30 and a weight 2 is fixed on an insulating plate 9 by a rigid metal body 30, a fixing screw 5, and a nut 15.

The weight 2 and the metal rigid body 30 are thermally balanced and mechanically joined by a metal fixing means including a fixing screw 5 and a nut 15.

Further, the electrodes 3a and 3b of the piezoelectric elements 4a and 4b are connected to the input end of the charge amplifier 6 via output lines 13 and 14, respectively. The outer electrodes 3a of the two symmetrical piezoelectric elements 4a, 4b are electrically connected to each other by a line (not shown).

A charge amplifier 6 is also mounted on the insulator 9. A ground circuit of this charge amplifier 6 is connected to the conductive case 1. Charge amplifier 6 is piezoelectric element 4a
, 4b is used to preamplify the voltage (detection signal) generated by the circuit 4b, and is not easily affected by power supply voltage fluctuations and noise.

The output of charge amplifier 6 is applied to the input terminal of amplifier 7. An amplifier 7 is also mounted on the insulating plate 9, and the output terminal of this amplifier 7 is connected to a three-terminal capacitor 8a.
, are connected to the control device 11 via the feedthrough capacitor IOB.

The power supply line 31 is connected to the positive terminal of the stabilized power supply 12 in the control device 11.
．． Power is supplied to the piezoelectric acceleration sensor via the feedthrough capacitor 10a and the three-terminal capacitor 8a.

The negative electrode of stable specific gravity 'fA12 is grounded. This negative electrode is connected to the conductive case 1 via a ground wire 32. This conductive case 1 is connected to an insulating plate 9 through a ground wire 16.

Further, each ground of the electronic circuit on the insulating plate 9 is connected to the ground wire 32 of the control device 11 via the conductive case 1, and a noise filter (not shown) is used to provide a shielding effect. Reduces the influence of external noise.

The ground terminals of the three-terminal capacitors 8a and 8b are grounded, and the ground terminals of the feedthrough capacitors 10a and 10b are connected to the conductive case 1.

FIG. 2 is a circuit diagram showing a specific configuration of the charge amplifier 6 and its peripheral circuits. In FIG. 2, the piezoelectric elements 4a and 4b are floated above the ground potential by an insulating plate 9, as shown in FIG. 1, and the potential of one electrode is fixed at the potential divided by resistors R1 and R2. There is.

Further, 20 is an operational amplifier with FET input, and its (G) input terminal and (C) input terminal are connected via resistors R3 and R4. Since the potentials of both the ) input terminal and (c) input terminal move in conjunction with each other, the influence of fluctuations in the power supply voltage is reduced.

The connection point between the resistors R3 and R4 is connected to the connection point between the resistors R1 and R2. As described above, the resistors R1 and R2 are connected between the power source and the ground in order to fix the potential of one electrode of the piezoelectric elements 4a, 4b.

A capacitor CI is connected in parallel to the resistor R3. The capacitor C1 is used to convert changes in the charges of the piezoelectric elements 4a and 4b into voltage, and to increase the time constant to an optimum value in order to further lower the minimum detection frequency of the detected acceleration.

Moreover, between the output terminal and the H input terminal of the operational amplifier 20,
A parallel circuit of resistor R5 and capacitor C2 is connected. Since the impedance of capacitor C2 decreases at high frequencies, by setting the time constant of C2 and R5 to 5 Hz, for example, it can be set as a low-pass filter for removing unnecessary unsprung components when detecting acceleration in the vertical direction. , there is no need to add a special low-pass filter.

Even if you add a low-pass filter to the latter stage,
By matching the cutoff frequencies, it is possible to further optimize the filter characteristics for the second and third orders.

As mentioned above, the output of the operational amplifier 20 is amplified by the amplifier 7, and the output of the amplifier 7 is input to the control device II (Fig. 1) via the three-terminal capacitor 8b and the feedthrough capacitor 10b. Stabilized power supply 1 for control device 11
The feedthrough capacitor 10 is passed through the ground wire 32 from the negative terminal of 2.
It is connected to the ground wire of b.

Further, power is supplied to the piezoelectric acceleration sensor from the positive electrode of the stabilizing type a12 through the feeder line 31 feedthrough capacitor 10a and the three-terminal capacitor 8a.

Next, the operation will be explained. There is an air layer inside the conductive case 1, the temperature change outside the conductive case l due to the metal case is moderated, and the piezoelectric elements 4a, 4b
is a metal weight 2. Rigid metal body 30, fixing screw 5. The nut 15 stores and retains heat, which has the effect of maintaining a temperature balance between the piezoelectric elements 4a and 4b and slowing temperature changes.

Furthermore, since the piezoelectric elements 4a and 4b are held by the insulating plate 9, they have the effect of being thermally isolated from the conductive case l.

By connecting the piezoelectric elements 4a and 4b symmetrically and in parallel, pyroelectricity is canceled out. The charges generated in the piezoelectric elements 4a and 4b in response to acceleration are converted into voltage changes by the capacitor C1, multiplied by (1+R4 times) by the operational term C''/R5 and the multiplier 20, and further amplified by the amplifier 7. It is input to the control 1ffll device 11 via the terminal capacitor 8b and the v1 capacitor 10b.

In this case, the minimum frequency of the detected acceleration can be arbitrarily set using the capacitor C1 and the resistor R3. For example, 0.2! C1=0.047μ so that it is about Iz
It is sufficient to set F, R3=15MΩ.

This allows you to use the
Unnecessary drift voltage due to temperature can be optimally removed.

Furthermore, by making the resistor R3 smaller than the input impedance of the operational amplifier 20, it is possible to arbitrarily and optimally set the low-frequency time constant. The input impedance of the FET-powered operational amplifier 20 is, for example, 109Ω or more, which is sufficient for this purpose.

Furthermore, the time constant C2 of the capacitor C2 and the resistor R5,
For example, by setting R5 to 5) 1z as described above, unnecessary unsprung components can be removed when vertical acceleration is detected.

Furthermore, since the charge amplifier 6 is configured as shown in FIG.
In addition, the low frequency characteristics of the charge amplifier 6 can be adjusted by using a simple structure in which the capacitor CI, which converts changes in the charges of the piezoelectric elements 4a and 4b, is connected to the positive phase and anti-correlation of the operational amplifier 20 of the FET input. C.I.
and the discharge resistor R3 can be set optimally, which has the effect of omitting one stage of a special bypass filter for pyroelectric countermeasures.

Furthermore, the simple configuration of limiting the gain of the charge amplifier 6 in the high range has the effect of omitting one stage of a low-pass filter for removing the influence of external unwanted vibrations.

By the way, when using a conventional impedance conversion circuit, it is not as easy to set the low-frequency time constant as in the present invention, and for this reason, it is necessary to specially provide a bypass filter circuit and a low-pass filter circuit at the subsequent stage. Moreover, it has the disadvantage of being weak against power supply voltage fluctuations, but the present invention has the effect of solving these disadvantages with a single stage of charge amplifier 6.

In other words, it is possible to obtain an acceleration sensor that is resistant to fluctuations in power supply voltage, resistant to temperature drift, and does not amplify unnecessary vibration noise, and is optimal for use in automobiles.

On the other hand, the potential of the piezoelectric elements 4a, 4b is set to be floating, and the charge amplifier 6 is configured to convert the change in electric charge generated in the piezoelectric elements 4a, 4b into voltage and amplify it accurately regardless of fluctuations in the power supply voltage. Therefore, it is resistant to fluctuations in power supply voltage, and there is no need to provide a special stabilized power supply exclusively for the acceleration sensor.For example, as in the illustrated embodiment, the stabilized rA12 of the control device 11 can be shared, Even if it is supplied from the power supply line 31, it can be operated stably.

FIG. 3 is a cross-sectional view of a portion mainly consisting of a piezoelectric element, showing another embodiment of the metal rigid body 30. As shown in FIG. In the case of FIG. 3, the metal rigid body 30 is formed into a "U" shape as shown, and the insulating plate 9 is inserted into the metal rigid body 30 so that the insulating plate 9 is held between the metal rigid body 30. ing.

The piezoelectric elements 4a, 4b and weight 2 are placed on the upper surface of this rigid metal body 30, and are tightened with fixing screws 5 and nuts (the nuts are not shown in FIG. 3).

By doing so, the piezoelectric element 4a.

This has the effect of further optimizing the temperature balance of 4b.

In addition, in each of the above embodiments, the capacitor C1 and the resistor R
It is desirable that the cutoff frequency on the low frequency side of the detected acceleration is set to 0.1 to 0.311z, and the cutoff frequency on the high frequency side is equal to or higher than the vehicle's spring main resonance frequency and is equal to or higher than the unsprung resonance frequency. It is preferable to set the following.

Furthermore, in each of the above embodiments, the piezoelectric element 4a.

The temperature coefficient of capacitance of the capacitor CI for converting the change in the charge of the capacitor 4b into a corresponding change in the voltage of the capacitor may be made positive, thereby canceling out the temperature characteristic of the detection sensitivity.

〔Effect of the invention〕

As described above, according to the present invention, a plurality of piezoelectric elements are formed into a sandwich structure with a weight and a rigid metal body, are attached to an insulating plate, and are configured to be in a non-conductive state with a conductive case that also serves as a shield. , has a simple structure that seals noise resistance, and also has the effect of softening the effects of pyroelectricity caused by temperature changes, and canceling out pyroelectricity by using a plurality of piezoelectric elements.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of an acceleration sensor according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a specific circuit configuration mainly consisting of a charge amplifier part in the above acceleration sensor.
FIG. 3 is a sectional view of a piezoelectric element in an acceleration sensor according to another embodiment of the present invention. l... Conductive case, 2... Weight, 4a, 4b.
... Piezoelectric element, 5... Fixing screw, 6... Charge amplifier, 9... Insulating plate, lO... Nut, 30...
・Metal rigid body, 31... Power supply line. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A plurality of piezoelectric elements connected in parallel that generate a voltage using a weight according to acceleration, a charge amplifier that amplifies the signal generated by the piezoelectric element, and a conductive case connected to a ground circuit of the charge amplifier. A rigid metal body that supports the weight and the piezoelectric element, and the weight and the rigid metal body are thermally balanced by a fixing means and mechanically joined, and the rigid metal body is fixed to the conductive case in a non-conductive manner. Acceleration sensor equipped with an insulating plate for.