JPS62291535A - Piezoelectric element applied sensor apparatus - Google Patents

Abstract

PURPOSE:To obtain the title apparatus having no sensitivity irregularity, by electrically connecting a sensitivity control condenser having predetermined capacity to a piezoelectric element in parallel. CONSTITUTION:A cable 2 is divided into a ground wire 21 and a signal wire 22 at the inlet of a connector 30 and both wires are respectively connected to the ground side terminal 31 and the signal side terminal 32 of the connector 30. The terminals 31, 32 are connected to the terminals in the connector 5 on an amplifier assembly 40 in an interdigitated state to achieve function transmitting a detection signal. Ground side and signal side glands 33, 34 are respectively provided to the base parts of the terminals 31, 32 and a sensitivity control condenser 35 is provided between said glands so as to be held therebetween and electrically connected to a cylinder internal pressure sensor 1 in parallel. By this constitution, when the actual sensitivity of a piezoelectric element is larger than desired sensitivity, a large capacity condenser is connected and, when the actual sensitivity is smaller, a small capacity condenser is connected to obtain a sensor apparatus free from sensitivity irregularity and having desired sensitivity.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a sensor device having a piezoelectric element, and particularly to a sensor device having a piezoelectric element that generates a detection signal in response to received pressure. The present invention relates to a sensor device comprising a sensor and a signal amplification means for amplifying the detection signal.

[Conventional technology]

Conventionally, example 4354) is used as a sensor device having a piezoelectric element.
, this device connects a cylinder pressure sensor l that detects the cylinder pressure of an internal combustion engine, a voltage amplifier 6 that amplifies the detection signal from the cylinder pressure sensor 1, and transmits the detection signal. It consists of a cable 2.3 and a connector 4.5 for connecting cable 2 and cable 3. Here, the voltage amplifier 6 is installed in an engine control unit (not shown).

The cylinder pressure sensor 1 has a ring-shaped washer type, and the sixth
As shown in the figure, the ignition plug 103 and the cylinder head 101 of an automobile engine etc. are interposed and sandwiched, and the pressure change in the combustion chamber 102 is transmitted between the ignition plug 103 and the cylinder head 101.
It is detected as a tightening load fluctuation between 1 and 1.

An example of the internal structure of the cylinder pressure sensor 1 is shown in FIG. The cylinder pressure sensor 1 has a casing 14 made of stainless steel or the like.
A piezoelectric element 11 is placed on both sides of the reed plate 13 from which the signal is taken out, and a pressure receiving plate 12 that also serves as a ground electrode is placed on the outside of the lead plate 13.
It is connected to Zare 1131D cable 2. The cylinder pressure sensor l generates a negative charge -Q proportional to the tightening load fluctuation (=pressure change in the combustion chamber 102) as a detection signal.

The detection signal is transmitted via the cable 2.3 and the connector 4.5 to a voltage amplifier 6 as signal amplification means, where it is converted into a voltage signal V. If an inverting amplifier using an operational amplifier is used as the voltage amplifier 6, the voltage signal V becomes a signal proportional to the tightening load of the cylinder pressure sensor 1. In other words, this piezoelectric element application sensor device attempts to obtain a voltage signal proportional to the cylinder pressure of an internal combustion engine.

The equivalent circuit of the sensor device shown in FIG. 5 is shown in FIG.
The cylinder pressure sensor 1 has a current source (current i = -d Q /
d t = A d F / d t ), which can be expressed by the capacitance Cs and insulation resistance Rs of the sensor coupled in parallel.

The voltage amplifier 6 has an input resistor R1 using an operational amplifier.
and a feedback resistor R2, and its output voltage is V. Furthermore, the cable 2.3 also has capacitance, and the combined capacitance is defined as CL.

Therefore, the output voltage V is expressed as when the insulation resistance R3 is sufficiently large, and the ratio of the resistances R1 and R2 of the voltage amplifier 6 is
The relationship from the sensor tightening load change ΔF to the output voltage V is determined by the capacitance Cs of the cylinder pressure sensor 1, the sum C of the capacitance of the cable 2.3, and the sensor sensitivity A.

[Problem that the invention seeks to solve]

By the way, in such a conventional sensor device, there is a variation in the sensitivity A of the in-cylinder pressure sensor l, which is adjusted by adjusting the length of the cable 2.3 (proportional to Ct) and the gain R2/R1 of the voltage amplifier 6. Therefore, it is difficult to eliminate the problem. Therefore, when the detection signal of the cylinder pressure sensor 1 is amplified by the voltage amplifier 6, the sensitivity variation is further expanded, making it impossible to accurately measure the cylinder pressure. It is necessary to select the sensitivity of the cylinder pressure sensor l so as to keep the pressure within the range.

There was a problem in that the yield during manufacturing of the cylinder pressure sensor 1 was reduced.

The present invention has been made by focusing on such conventional problems, and a sensitivity adjustment capacitor corresponding to the sensitivity of the in-cylinder pressure sensor 1 is connected electrically in parallel to the piezoelectric element, thereby reducing overall sensitivity variation. This was done with the aim of solving the above problem by keeping it within a predetermined range.

[Means for solving problems]

The present invention relates to a sensor device including a sensor having a piezoelectric element that generates a detection signal in response to received pressure, and a signal amplification means to amplify the detection signal, which has a predetermined capacity for adjusting the sensitivity of the sensor device. A sensitivity adjustment capacitor is electrically connected in parallel to a piezoelectric element.

[Effect]

When the piezoelectric element of the sensor receives pressure, the piezoelectric element is amplified to a predetermined magnitude by the signal amplification means. The sensitivity of the piezoelectric elements used at this time varies among products, and it does not necessarily have the desired sensitivity, and the signal amplified by the signal amplification means will have an even greater difference. Adjustment is required to obtain the correct signal. In the present invention, this adjustment is performed by appropriately setting the capacitance of a sensitivity adjustment capacitor connected in parallel to the piezoelectric element. In other words, if the actual sensitivity of the piezoelectric element is greater than the desired sensitivity, a capacitor with a predetermined large capacitance is connected, and if the actual sensitivity is smaller than the desired sensitivity, a capacitor with a predetermined small capacitance is connected. As a result, a sensor device having a desired sensitivity without sensitivity variations can be obtained.

〔Example〕

Examples according to the present invention will be described below.

FIG. 2 shows a first embodiment according to the present invention,
Piezoelectric element application sensor device Ito tips related to unimplemented examples -
74+ 7,,-,・7, 1 ^ “Cast 1
[7-7--7-,・7 7 A ^ Wound,
It is composed of

The sensor system 10 includes a cylinder pressure sensor l for detecting the cylinder pressure of an internal combustion engine, a cable 2, and a capacitor built-in connector 30 that contains a sensitivity adjustment capacitor.

The amplifier array 40 includes a connector 5 connected to the capacitor built-in connector 30, a cable 3, and a voltage amplifier 6 as a signal amplification means.

FIG. 3 shows details of the capacitor built-in connector 30. The cable 2 is divided into a ground line 21 and a signal line 22 for transmitting a detection signal at the entrance of the connector 30, and a ground side terminal 31 and a signal side terminal 32 of the connector 30. These are connected to each other by caulking or other methods. These terminals 31 and 32 are connected by fitting with the terminals in the connector 5 on the amplifier array 40 side and play the role of transmitting the detection signal.At the base of the terminals 31 and 32, there are a ground side land 33 and a signal side land 34, respectively. are provided, and a sensitivity adjustment capacitor 35 is provided sandwiched therebetween. This example uses chip capacitors. As a result, the sensitivity adjustment capacitor 35 is connected to the cylinder pressure sensor l.
will be electrically connected in parallel.

Next, the operating principle of this embodiment will be explained.

In the equivalent circuit of this embodiment shown in FIG. 1, the capacitance of the sensitivity adjustment capacitor 35 is C&Li, and the other parts are the same as in the conventional example. In this equivalent circuit, if the insulation resistance R5 is sufficiently large, the output voltage V is expressed as follows.

In other words, CalJ is added to the denominator of equation (1) above, and by selecting an appropriate capacitance value for CaU, the desired relationship from the tightening load fluctuation ΔF to the output voltage V can be obtained. Can be done.

Note that, from equation (2), adding the sensitivity adjustment capacitor 35 will reduce the overall sensitivity, but if the sensitivity is to be increased, the gain R2/R1 of the voltage amplifier 6 is set high in advance.

Also, the low-frequency cut-off frequency f0 of this equivalent circuit is f6 ” l/ (2w ” R3R1/ (R3+R
1) Fist (Cs +ct +CkiJ) ) ・
...(3) [Hz] is determined. Therefore, adding the sensitivity adjustment capacitor 35 changes the low cutoff frequency fc to the lower frequency side. Taking this into account as well, it is necessary to set the input resistance R1 of the voltage amplifier 6 so as to obtain the required low cut-off frequency f.

Next, a method of selecting the value of the capacitance Ca4 of the sensitivity adjustment capacitor 35 will be explained based on a specific example.

Table 1 describes the sensitivity A, capacitance C8, insulation resistance Rs, and capacitance CL of the cable 2.3 for six cylinder pressure sensors 1 with varying sensitivities.

The capacitance Cs of the six sensors is all 1000 pF, and the insulation resistance Rs of the six sensors are all IOMΩ, and the Δ1 lightning capacity NCL of the cable 23 between the capacitor and the eggplant is constant at 500 pF regardless of the sensor. . Sensor sensitivity ranges from 930pc/kg/f/cd to 1076pc/kg
Assume that the difference is within a range up to f/d.

Using these cylinder pressure sensors l, the output voltage V of the voltage amplifier 6 is set to l, OV/kg-f/cnl, and the low cut-off frequency fc+ is set to 50 at the maximum.
The frequency should be approximately 0Hz.

First, the input resistance R□ of the voltage amplifier 6 is determined based on the constraint of the low cut-off frequency fc. To do this, in equation (3), CadJ=
R5 and C5 in Table 1 so that fc=500 in the case of 0.
, CL can be substituted to find R1. Then,
Ω is obtained for R14217, and here Ω is obtained for R14217.
are selected.

Next, the feedback resistance R2 of the voltage amplifier 6 is determined from the conditions of output voltage v=1 and OV/kg fist f/cr4. Sensitivity A
Since it decreases when the sensitivity adjustment capacitor C&Ll is added, the cylinder pressure sensor NO05 has the lowest sensitivity A.
At least 1. when not adding Cad, l. OV/kg・
Make sure that f/crd is obtained. To select R2, v=1. Substitute Ω and ΔF=1kgφf/ for the sensitivity of OV/kg・f/crA, No. 5 (see Table 1), C&dJ=0, and R1=220 into equation (2). Then, Ω is obtained at R2 cape 355, and here, Ω is obtained at R2 = 360.
Select.

Next, to select the value C & dJ of the sensitivity adjustment capacitor 35, use a modified formula (2) to add Ω to R = 220, which was found earlier, and R2 = 360.
Ω, v=l, OV/kg lIf/CrA and Δ
F=1 kg@f/cm Further, substitute A, cs, and CL in Table 1 to find Cadj. The obtained results are also shown in Table 1.

The sensitivity adjustment capacitors 35 having the capacities Q C & dj thus obtained are connected to cylinder pressure sensors No. 1 to No. 1, respectively.
6, all of the cylinder pressure sensors No. 1 to No. 6, which have sensitivity variations, will have TE V = 1, O.
V/kg-f/CrAc7) Can be modified to have equal sensitivity to obtain equal output voltages.

Although the case where the sensitivity A fluctuates has been described here, even if the capacitance Cs of the sensor fluctuates, the sensitivity adjustment capacitor 35 can similarly adjust the sensitivity so that there is no fluctuation.

Also, if the target output voltage is within a predetermined tolerance range, for example 0.9
If you only need to keep it within the range of 5 to 1.05 V/kg-f/crd, prepare two to three types of sensitivity adjustment capacitors with different capacities, and adjust the capacitor according to the sensitivity variation of the sensor. You may select and use one of them.

Furthermore, a second example will be explained.

This embodiment does not use a cylinder pressure sensor in the form of a washer of a spark plug as in the first embodiment, but uses a pressure-detecting spark plug in which a pressure-sensitive element is embedded in the spark plug. FIG. 4 shows an example of a pressure detection spark plug 50. In this embodiment, a pressure sensitive element 53 made of a piezoelectric element is sandwiched between a metal shell 51 of the plug and an insulator 52. The detection signal is taken out from the cable 20.

In this embodiment, pressure is detected as follows. Combustion chamber 102
The insulator 52 is pushed upward in response to the combustion pressure, and this force acts as a compressive force on the pressure sensitive element 53 sandwiched between the metal shell 51 and the insulator 52.

Then, the pressure sensitive element 53 detects the change in the compressive force and transmits a detection signal to the cable 20.

In the first and second embodiments described above, since the sensitivity adjustment capacitor is housed in the connector on the sensor side including the piezoelectric element, it is possible to suppress variations in sensitivity to a small level using the sensor alignment alone. Therefore, the troublesome work of adjusting in combination with an amplifier controller including a voltage amplifier is unnecessary.

〔effect〕

As explained above, according to the present invention, the configuration is such that a sensitivity adjustment capacitor corresponding to the sensitivity of the piezoelectric element applied sensor is electrically connected in parallel with the piezoelectric element.
Variations in the sensitivity of the sensor device including the cable and voltage amplifier can be suppressed within a predetermined range by adjusting the capacitance of the sensitivity adjustment capacitor. Therefore, it becomes possible to accurately measure physical quantities such as pressure, and the tolerance for sensitivity variations in the piezoelectric element applied sensor device itself increases, resulting in the effect of improving the yield of sensor manufacturing. , \,

[Brief explanation of drawings]

FIG. 1 is an equivalent circuit diagram according to the first embodiment of the present invention, and FIG.
The figure is an overall view showing the first embodiment of the present invention; Fig. 5 is an overall view of the conventional example, Fig. 6 is a sectional view showing how the conventional example is used, Fig. 7 is an enlarged sectional view of the main part of Fig. 6, and Fig. 8 is an equivalent circuit diagram of the conventional example. be. l... Cylinder pressure sensor (including piezoelectric element) 2.3...
Cable 4.5... Connector 6... Voltage amplifier (signal amplification means) Patent applicant Nissan Motor Co., Ltd. Applicant Kuchiki Electronics Co., Ltd. Representative Patent attorney Uezumi Kao Tier diagram Figure 2 +p 4゜

Claims (1)

[Claims] In a sensor device comprising a sensor having a piezoelectric element that generates a detection signal in response to received pressure, and a signal amplification means to amplify the detection signal, a sensitivity adjustment device having a predetermined capacity for adjusting the sensitivity of the sensor device. A sensor device using a piezoelectric element, characterized in that a capacitor is electrically connected in parallel to a piezoelectric element.