JPH0639337Y2 - Acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an acceleration sensor using a piezoelectric element for detecting vibration and riding comfort for an automobile.

[Conventional technology]

Piezoelectric sensors are used to detect the vibration and riding comfort of automobiles.
For example, it is described in the book "Keras", Series No. 5 Ceramic Sensor '73, No. 32, published by Eresera Publishing Co., Ltd., P81-85 "Force and Acceleration Sensor (1)".

An acceleration sensor using such a piezoelectric sensor, a weight, and a charge amplifier is applied to, for example, an electronically controlled suspension that controls the riding comfort of an automobile.

When the piezoelectric sensor is applied to the electronically controlled suspension, the problem is how to solve the problem that the piezoelectric sensor has a high impedance and is vulnerable to external noise caused by its capacitive property.

Therefore, it has a built-in impedance conversion circuit,
A device such as grounding one electrode of the piezoelectric sensor on the case so that the case has a shielding effect has been devised.

[Problems to be solved by the device]

However, in this case, when a single battery power source is used as in an automobile and the body of the automobile is grounded, if one side electrode of the piezoelectric sensor is grounded to the case, The detection signal of changes with the ground as the center, while the amplifier amplifies, for example, at the point where the power supply voltage is divided in half, so it is difficult to separate the amount of change in the power supply voltage from the detection signal. However, there is a drawback that the signal is disturbed, and it becomes more susceptible to fluctuations in power supply voltage and noise.

In order to deal with this, the solution is to use a charge amplifier instead of an impedance conversion circuit, but the charge amplifier circuit has a practically difficult problem even in general use of both power supplies, and technically It was difficult.

Further, there is a problem in the circuit configuration for configuring the charge amplifier with a single power source and being strong against fluctuations in the power source voltage.

In addition, in order to optimally configure the above charge amplifier, it is necessary to float both electrodes of the piezoelectric sensor from the ground potential.In particular, when the case is grounded, how is it insulated from the case? The problem is whether the piezoelectric sensor is fixed to the case.

Also, when using an acceleration sensor with a piezoelectric sensor as a system combined with a suspension control device, the stabilized power supply of the suspension control device is effectively used, and in addition, induced noise on the power supply side and the ground side caused by wiring and the power supply voltage. The problem was how to eliminate the effects of fluctuations.

The present invention has been made to solve the above problems, and is resistant to fluctuations in power supply voltage, operates at a single power supply voltage and is also resistant to noise, and is optimal for use in combination with a vehicle suspension control device. The purpose is to obtain an acceleration sensor.

[Means for Solving the Problems]

The acceleration sensor according to the present invention is provided with a piezoelectric element that outputs a detection signal according to acceleration and a charge amplifier that amplifies the output signal of the piezoelectric element, which is attached to a conductive case with a weight through an insulating plate. It is a thing.

[Action]

The piezoelectric element in this invention is floated from the earth potential by an insulator, and the conductive case is set to the earth potential so as to have a shield effect, and the detection signal corresponding to the acceleration is taken out by the piezoelectric element without being affected by the fluctuation of the power supply voltage. It acts to suppress the influence of disturbance noise due to the charge amplifier.

〔Example〕

An embodiment 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 the embodiment. In FIG. 1, reference numeral 1 is a conductive case.

A piezoelectric element 4 and a weight 2 are attached to a predetermined portion of the conductive case 1 via an insulating plate 9 with a fixing screw 5 and a nut 15. As the insulating plate 9, a printed circuit board made of an epoxy substrate or a ceramic substrate is used. The piezoelectric element 4 is fixed to the conductive case 1 in a non-conductive manner by the insulating plate 9.

Electrodes 3a and 3b are provided on both front and back surfaces of the piezoelectric element 4.

The electrode 3b is pressed against the upper surface of the insulating plate 9, and the electrode 3a is a weight 2
And the piezoelectric element 4. The electrodes 3a and 3b are connected to the input ends of the charge amplifier 6 via the output lines 13 and 14, respectively.

The charge amplifier 6 is also attached to the insulating plate 9. Since the charge amplifier 6 preamplifies the detection signal of the piezoelectric element 4, it is used to reduce the influence of fluctuations in power supply voltage and noise.

Reference numeral 7 is an amplifier mounted on the insulating plate 9. This amplifier 7 is for amplifying the output of the charge amplifier 6, and its output end is a three-terminal capacitor 8b,
It is connected to the input terminal of the control device 11 via the feedthrough capacitor 10b.

12 is a stabilized power supply, and this stabilized power supply 12 is a control device 11
It is obtained from the stabilized power supply circuit (not shown) of the power supply line 12, the feed line 31, the feedthrough capacitor from the positive electrode of the stabilized power supply 12.
Power is supplied to the piezoelectric acceleration sensor via 10a and the three-terminal capacitor 8a.

The negative electrode of the stabilized power supply 12 is grounded and connected to the conductive case 1 via a ground wire 32. The conductive case 1 is connected to the insulating plate 9 via a ground wire 16.

With this configuration, the electronic circuits on the insulating plate 9, that is, the grounds of the charge amplifier 6, the amplifier 7, and the piezoelectric element 4 are connected to the ground wire 32 of the control device 11 via the conductive case 1. Therefore, when a noise filter circuit (not shown) is used as the shield effect, an effect of reducing the influence of external noise can be obtained.

The charge amplifier 6 is constructed as shown in FIG. In FIG. 2, the piezoelectric element 4 is floated above the ground potential, and the potential of the electrode 3b on one side is fixed to the potential divided by the resistors R1 and R2.

The (+) input terminal and the (-) input terminal of the operational amplifier 20 for FET input are connected through the resistor R3, and therefore the potentials of both the (+) and (-) input terminals are changed even if the power supply changes. , Which are linked to each other, reduce the effect of power fluctuations.

A capacitor C1 is connected in parallel with the resistor R3, and
The electrode 3a of the piezoelectric element 4 is connected to the (+) input terminal of the operational amplifier 20, and the electrode 3b is connected to the (-) input terminal of the operational amplifier 20 via the resistor R4.

The capacitor C1 is inserted in order to increase the time constant and set the optimum value for the purpose of lowering the minimum detection frequency of the detected acceleration.

A resistor R3 is placed between the output terminal of the operational amplifier 20 and the (-) input terminal.
Is connected, and the output of this operational amplifier 20 is amplifier 7,
It is adapted to be connected to the control device 11 via the three-terminal capacitor 8b and the feedthrough capacitor 10b.

The ground electrode of this feedthrough capacitor 10b is connected to the negative electrode of the stabilized power supply 12 of the connection device 11 via a ground wire 32.

Further, the power source terminal of the amplifier 7 is provided with a stabilized power source 12 via a three-terminal capacitor 8a, a feedthrough capacitor 10a, and a power supply line 31.
Is connected to the positive electrode of and is supplied with power.

Next, the operation will be described. The load of the weight 2 is applied to the piezoelectric element 4 by the acceleration, and a voltage corresponding to the change of the charge of the piezoelectric element 4 is generated between the electrodes 3a and 3b according to the acceleration,
This voltage is applied to the input terminal of the charge amplifier 6.

This charge amplifier 6 is an operational amplifier 20 used as a FET input.
The voltage corresponding to the change in the charge of the piezoelectric element 4 is applied between the (−) input terminal and the (+) input terminal of the operational amplifier 20.

This voltage is (1 + R5 / R4 times) multiplied by the operational amplifier 20, further amplified by the amplifier 7, and then the three-terminal capacitor 8b,
It is input to the control device 11 via the feedthrough capacitor 10b.

The potential of the piezoelectric element 4 is set to a floating state, and the charge amplifier 6 is configured to convert the change in the electric charge generated in the piezoelectric element 4 into a voltage and accurately amplify the voltage regardless of the change in the power supply voltage. It is strong against the fluctuation of and does not need a special stabilizing power supply for the acceleration sensor.

For example, even if the stabilizing power supply 12 of the control device 11 is shared and the power is supplied by the power supply line 31, the stable operation can be achieved.

Further, since the charge amplifier 6 uses the operational amplifier 20 of the FET input, the low frequency detection characteristic can be arbitrarily set by an external component, and there is a strong effect on the fluctuation of the power supply voltage.

The acceleration sensor using the piezoelectric element 4 of the embodiment shown in FIG. 1 and FIG. 2 is intended to detect only the vertical acceleration shown in FIG. Since the force is applied to the piezoelectric body due to the rolling due to
Output will be generated.

That is, when the electrode 3b on one side of the piezoelectric element 4 is directly fixed to the metal rigid body which is the conductive case 1 with the fixing screw 5 as in the conventional case, the action of the weight 2 is effective for the piezoelectric element 4 vertically. Although the left and right sides can be configured to act insensitively, there is a problem with a method of electrically insulating the conductive case 1 and fixing it mechanically and stably.

Although it is difficult to completely reduce the lateral detection sensitivity to zero, it can be reduced, and Fig. 3 shows that the detection of vertical acceleration is stabilized and unnecessary lateral sensitivity is reduced. An example of is shown.

In the embodiment shown in FIG. 1, the electrodes 3a, 3
The piezoelectric element 4 sandwiched in b is placed and fixed by the fixing screw 5 and the nut 15. However, when a force is applied in the lateral direction, the roll is likely to occur.

Therefore, as shown in FIG. 3, the plate 30 for reinforcing the fixed portion is formed in a "U" shape, and the plate 30 is formed.
Insert the insulating plate 9 inside, and place the piezoelectric element 4 on the plate 30.
And the plate with the fixing screw 5 with the weight 2 placed
Rolling can be reduced by fixing to 30 and the insulating plate 9.

In this case, the plate 30 is made of a material (for example, metal) that can be regarded as a rigid body, and since the plate 30 is fixed to the conductive case 1 via the insulating plate 9, the plate 30 is kept insulated from the conductive case 1. On the other hand, mechanically, it is stably fixed with screws or the like (not shown), and the conventional mechanical acceleration detection capability can be realized.

Incidentally, in each of the above-mentioned embodiments, the case where the ground wire 32 is provided is described in consideration of particularly high-precision applications, but in this case,
If the conductive case 1 is insulated and attached to the vehicle body, the ECU
One-point grounding can be realized only with the (electronic control device), a current due to the common impedance does not flow in the ground line 32, and it is possible to perform measurement with less fluctuation of the power supply voltage.

If the detection accuracy up to that level is not required, the conductive case 1
It goes without saying that the car can be grounded.

Furthermore, in each of the above-described embodiments, the case where the weight 2 and the piezoelectric element 4 are fixed to the same insulating plate 9 (printed circuit board) as the detection circuit has been described, but the same effect is expected even if they are fixed by different insulators. It goes without saying that you can do it.

Further, in each of the above-described embodiments, the case of detecting the vertical acceleration is described, but it goes without saying that the same effect can be expected in the case of detecting the left, right, front, and rear accelerations.

On the other hand, the charge amplifier 6 may have any configuration other than the circuit configuration shown in FIG. 2 as long as the change in the charge of the acceleration sensor is converted into a floating change in voltage. .

Furthermore, the structural shape of the metal rigid body is not limited to the shape of each of the above-described embodiments, and has a function of effectively detecting a change in force generated by the acceleration composed of the weight 2 and the piezoelectric element 4 with a reduced loss. It goes without saying that it is good as long as it is one.

[Effect of device]

As described above, according to the present invention, the charge amplifier circuit composed of a single power supply is housed in the conductive case of earth potential that also functions as a shield for the sealing circuit, and the potential of both electrodes of the piezoelectric element is grounded to the case ground. Insulation sensor is installed on the device and is configured to stably detect only the detection signal component irrespective of fluctuations in the power supply voltage, and then an acceleration sensor that operates stably in a use environment where noise and voltage changes such as in automobiles can be obtained. effective.

[Brief description of drawings]

FIG. 1 is a configuration explanatory view of an acceleration sensor according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a concrete circuit configuration mainly including a charge amplifier portion in the acceleration sensor.
FIG. 3 is a sectional view of a portion of a piezoelectric element in an acceleration sensor according to another embodiment of the present invention. 1 ... Conductive case, 2 ... Weight, 4 ... Piezoelectric element,
6 ... Charge amplifier, 9 ... Insulation plate, 31 ... Feed line. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of utility model registration request] 1. A piezoelectric element that generates a voltage by a weight of a weight according to acceleration, a charge amplifier that amplifies a signal generated by the piezoelectric element, and a power supply line that supplies a single-polarity power source to the charge amplifier. An acceleration sensor comprising: a conductive case connected to a ground circuit to the charge amplifier; and an insulating plate for fixing the weight and the piezoelectric element to the conductive case in a non-conductive state.