JPH0830713B2 - Acceleration sensor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor for measuring or detecting running acceleration of an automobile equipped with an internal combustion engine.

2. Description of the Related Art FIGS. 5 to 15 show the structure of a conventional acceleration sensor. FIG. 5 is a plan view of a conventional acceleration sensor, FIG. 6 is a front sectional view taken along line VI-VI in FIG. 5, and FIG. 7 is a side sectional view taken along line VII-VII in FIG. FIG. 8 is a plan view of a main part of the conventional example, FIG. 9 is a front sectional view of the main part of the conventional example, FIG. 10 is a plan view of a piezoelectric ceramic element for sensor output in the conventional example, and FIG. 11 is a conventional example. Fig. 12 is a plan view of a piezoelectric ceramic element for pyroelectric cancellation in Fig. 12, Fig. 12 is a plan view of a diaphragm in a conventional example, Fig. 13 is a sectional view of the diaphragm,
Fig. 14 is a plan view showing another example of the conventional diaphragm.
FIG. 15 is a cross-sectional view of the diaphragm shown in FIG. In these figures, 1 is a base, and an annular projection 3 having a positioning hole 2 is formed in the center of the surface thereof. Reference numeral 4 denotes a diaphragm, the central portion of which is fixed to the annular projection 3 of the base 1 by means such as welding. Reference numeral 5 is a piezoelectric ceramic element for sensor output, which is fixed to the upper surface of the diaphragm 4. As shown in FIG. 10, the piezoelectric ceramic element 5 is formed in a donut shape having a round hole 6 in the center thereof, and the surface thereof has an annular shape for a positive electrode 7 for sensor output and a positive electrode 8 for driving the piezoelectric element. It is divided into two.

The negative electrode 9 on the entire back surface of the piezoelectric ceramic element 5 is conductively bonded to the front surface of the vibration plate 4 with the round hole 6 fitted in the outer circumference of the annular bead 10 formed in the central portion of the vibration plate 4. ing. Reference numeral 11 denotes a piezoelectric ceramic element for canceling pyroelectricity. As shown in FIG. 11, the piezoelectric ceramic element 5 has the same area as the positive electrode 7 of the piezoelectric ceramic element 5 and also has a round hole 12 in the center thereof. It has a plus electrode 13 and a minus electrode 14 on the back surface. The piezoelectric ceramic element 11 is
The positive electrode 13 side of the front surface is connected to the rear surface of the vibration plate 4, and the circular bead 15 formed in the central portion thereof is fitted with the round hole 12 so as to be conductively bonded.

As shown in FIGS. 12 and 13, the vibrating plate 4 has a positioning hole 16 of the same diameter as the positioning hole 2 of the base 1 at the center of the metal disk, and a concentric annular bead around the positioning hole 16. 10 and
15 are formed on the front surface and the back surface, respectively, in order of increasing diameter. As shown in FIGS. 14 and 15, the diaphragm 4 may be provided with an upward flange 17 at its periphery to increase the output of the acceleration sensor.

The positive electrode 7 of the piezoelectric ceramic element 5 and the negative electrode 14 of the piezoelectric ceramic 11 are connected to the lead frame 18,
The sensor output lead pin is connected to 19 by soldering 20 and 21, and via the insulating embedded lead pin 22 and the circuit board 23.
Connected to 24. This serves to cancel the electric charge generated in the plus electrode 7 of the sensor output piezoelectric ceramic 5 due to the pyroelectric phenomenon under the influence of the ambient temperature.

25 is a lead pin for driving the piezoelectric ceramic element,
It is connected to the plus electrode 8 of the piezoelectric ceramic element 5 via a lead frame 26 by solder 27. 28 is a circuit board
The power supply lead pin 23 and the ground lead pin 29 are connected to the circuit board 23, respectively. 30, 31
Is an embedded lead pin for supporting the circuit board 23. The circuit board 23 is provided with an impedance conversion circuit, an output amplification circuit, a filtering circuit, and the like.

Of the lead pins, 22, 24, 25, 28, 30, 31 are the base 1
Is insulated and hermetically fixed by means such as a sealing glass 32, and only the ground lead pin 29 is electrically connected by means such as brazing. Reference numeral 33 is a sealing glass for sealing the positioning hole 2 of the base 1. Power is supplied through the power supply lead pin 28 and the ground lead pin 29.

34 is a cap, the flange 35 of the periphery of which is the base 1.
Is fixed to the entire circumference by means such as resistance welding or cold pressure welding. As a result, the space 36 containing the piezoelectric ceramic elements 5 and 11 and the circuit board 23 is sealed.

The acceleration sensor having such a configuration is used by being attached to the vehicle body of an automobile with a bolt 38 and a washer 39 through a mounting hole 37 formed in the base 1.

Next, the operation of the above conventional example will be described. The acceleration generated by traveling of a car or the like is transmitted via the base 1 to the diaphragm 4
Is transmitted to the diaphragm 4, and the diaphragm 4 is bent. The bending of the diaphragm 4 alternately applies a tensile force and a compressive force to the piezoelectric ceramic elements 5 and 11, so that electric charges are generated in the piezoelectric ceramic elements 5 and 11. This charge is converted into a voltage by the impedance conversion circuit of the circuit board 23 and output through the filtering circuit and the amplification circuit so as to have a required band and an optimum output level, and a sensor output is obtained.

Further, since the piezoelectric ceramic has a pyroelectric phenomenon in which electric charges are similarly generated even when the temperature changes, in order to reduce this, this acceleration sensor connects the piezoelectric ceramic elements 5 and 11 with polarities opposite to each other. The generated charges are canceled.

Further, since an acceleration sensor used in an automobile or the like requires particularly high accuracy and quality, the positive electrode of the piezoelectric ceramic element 5 is used for sensor output so that the controller side can check whether or not it operates reliably. Electrode 7
And an electrode 8 for driving the element, and by inputting an appropriate signal from the transmitter circuit on the controller side to the driving electrode, a corresponding driving output appears on the sensor output electrode 7 and the sensor output Fault diagnosis is possible.

As described above, even the above-described conventional acceleration sensor can measure or detect acceleration in an automobile or the like.

However, in the above-described conventional acceleration sensor, the electrodes 9 and 13 on one side of the piezoelectric ceramic elements 5 and 11 are on the base 1.
Therefore, there is a problem in that noise is easily picked up through the base 1 and the cap 34, and when the noise is picked up by the vehicle body, the noise picked up by the vehicle body itself easily affects the sensor characteristics.

The present invention solves such a conventional problem, and an object of the present invention is to provide an acceleration sensor that is not easily affected by external noise.

Means for Solving the Problems In order to achieve the above object, the present invention has an insulative housing having an opening on the upper surface, and a shape including the inner wall surface of the opening of the housing and having the upper surface opened. A metal shield case fixed to the inner wall surface, and a resin base fixed inside the metal shield case,
A sub-base integrally formed on this base, a diaphragm whose central portion is fixed to the sub-base, and two positive and negative electrodes that are conductively bonded to each other on the front and back surfaces of the diaphragm. Of piezoelectric ceramic elements, lead terminals respectively connected to the electrodes of these piezoelectric ceramic elements, a circuit board for amplifying and filtering a signal output through these lead terminals, and an opening of the metal shield case. And a metal upper plate for covering.

Action According to the present invention, therefore, the positive and negative electrodes of the piezoelectric ceramic element are electrically insulated via the base, and the piezoelectric ceramic element and the circuit board are shielded by the metal case. Therefore, it is possible to cancel the pyroelectric phenomenon of the piezoelectric ceramic element that occurs due to a change in ambient temperature, and to eliminate the noise due to the pyroelectric phenomenon, in addition to having the effect of being less susceptible to external noise.

Embodiment FIG. 1 is a plan sectional view of an acceleration sensor showing an embodiment of the present invention, FIG. 2 is a front sectional view taken along line II of this embodiment, and FIG. 3 is line II-II of this embodiment. Side sectional view,
4A and 4B are a plan view and a front sectional view of the diaphragm 51, respectively. The diaphragm 51 shown in FIGS. 1 to 4b.
Since the positioning annular projections 81 and 82 and the center hole 83 of the piezoelectric ceramic elements 60 and 61 which are molded in the same manner as in the conventional example, description thereof will be omitted. 55 is a sub-base,
An annular protrusion 68 is provided in the substantially central portion of the surface. Sub base
55 is integrally molded with the base 53 together with the terminals 54, 69 and 70. Reference numeral 51 denotes a diaphragm fixed to the annular protrusion 68 of the sub-base 55 by being electrically insulated and fixed from the base 53, a piezoelectric ceramic element 60 for sensor output is fixed on the front surface thereof, and a pyroelectric element on the back surface thereof. The canceling piezoelectric ceramic element 61 is fixed. The negative electrode of the piezoelectric ceramic element 60 is conductively adhered to the surface of the diaphragm 51, and the positive electrode of the piezoelectric ceramic element 61 is conductively bonded to the rear surface of the diaphragm 51. The sensor output positive electrode 60a of the piezoelectric ceramic element 60 and the negative electrode of the piezoelectric ceramic element 61 are connected to the sensor output terminal 74 via the lead frames 72, 73 and the circuit board 62, respectively.
Reference numerals 64 and 66 denote soldered portions between the lead frames 72 and 73 and the piezoelectric ceramic elements 60 and 61, respectively. The electrode of the piezoelectric ceramic element 60 to which the lead frame 72 is connected becomes the output electrode 60a. 75 is a power supply terminal of the circuit board 62, and 76 is a ground terminal, which are connected to the circuit board 62, respectively. The terminals 74, 75 and 76 are all integrally formed with the housing 67. Reference numeral 85 is a pin for supporting the circuit board 62. Reference numeral 57 denotes a metal shield case, which is fixed to the housing 67 and the base 53 by adhesion or the like. Reference numeral 58 denotes an upper plate which is ring projection welded to the metal shield case 57 at the welded portion 65. 77 is a terminal formed by cutting and raising from the diaphragm 51,
Lead frame 79 by means such as soldering (78 parts)
It is connected to the. Reference numeral 52 denotes a drive terminal for applying a voltage to the piezoelectric ceramic element 60 to vibrate it for the purpose of self-checking the sensor characteristics, and is connected to the drive electrode 60b of the piezoelectric ceramic element 60 via the lead frame 80.

The acceleration sensor having the above structure is attached to the vehicle through the attachment holes 56a and 56b. 71a and 71b are mounting holes
Shown are metal rings inserted into 56a, 56b.

The operation in the above embodiment is the same as the conventional one. That is, the acceleration generated by the traveling of the automobile or the like is transmitted to the diaphragm 51 via the housing 67, the base 53 and the sub-base 55, and gives the diaphragm 51 a flexure. The bending of the diaphragm 51 alternately applies a tensile force and a compressive force to the piezoelectric ceramic elements 60 and 61.
And 61 generate charge. This charge is converted into a voltage by the impedance conversion circuit of the circuit board 62 and output through the filtering circuit and the amplification circuit so as to have a required band and an optimum output level, and a sensor output is obtained.

Here, according to the above-described embodiment, the vibration plate 51 is electrically insulated from the base 53 through the sub-base 55 so that the piezoelectric ceramic elements 60 and 61 are electrically insulated from the base 53. In addition, since the diaphragm 51 and the circuit board 62 are shielded by the metal shield case 57 and the upper plate 58, it is less susceptible to external noise such as electromagnetic waves and the characteristics are stable.

EFFECTS OF THE INVENTION As is apparent from the above-described embodiment, the present invention has a structure in which both positive and negative electrodes of a piezoelectric ceramic element are electrically insulated from the base, and the piezoelectric ceramic element and the circuit board portion are shielded by a metal case. Since the sensor characteristics are less likely to be affected by external noise, the pyroelectric phenomenon of the piezoelectric ceramic element that occurs due to changes in ambient temperature can be canceled, noise due to pyroelectric phenomenon can be eliminated, and the characteristics are stable. This has the effect of providing an extremely reliable acceleration sensor.

[Brief description of drawings]

FIG. 1 is a plan sectional view of an acceleration sensor showing an embodiment of the present invention, FIG. 2 is a front sectional view taken along line II of the present embodiment,
FIG. 3 is a side sectional view taken along line II-II of this embodiment, and FIG.
FIGS. A and b are a plan view and a front sectional view of a diaphragm used in this embodiment, FIG. 5 is a plan view of a conventional acceleration sensor, and FIG. 6 is a front view taken along line VI-VI of FIG. Sectional view, FIG. 7 is a side sectional view taken along the line VII-VII of FIG. 5, FIG. 8 is a plan view of the main part of the conventional example, and FIG. 9 is a front sectional view of the main part of the conventional example. 10 is a plan view of a piezoelectric ceramic element for sensor output in a conventional example, FIG. 11 is a plan view of a piezoelectric ceramic element for pyroelectric cancellation in a conventional example, FIG.
FIG. 13 is a plan view of the diaphragm in the conventional example, FIG. 13 is a cross-sectional view of the diaphragm, FIG. 14 is a plan view showing another example of the diaphragm in the conventional example, and FIG. 15 is the vibration shown in FIG. It is sectional drawing of a board. 51 …… Vibrator, 52 …… Drive terminal, 53 …… Base, 54,
69, 70 …… Terminal, 55 …… Sub base, 56a, 56b ……
Mounting hole, 57 …… Metal shield case, 58 …… Upper plate, 60,
61 ... Piezoelectric ceramic element, 60a ... Output electrode, 60b ...
… Drive electrodes, 62 …… Circuit board, 64, 66, 78 …… Soldering part, 67 …… Housing, 68 …… Annular protrusion, 71a, 7
1b …… Metal ring, 72,73,79,80 …… Lead frame, 74,75,76 …… Terminal, 77 …… Terminal, 81,82…
… Positioning annular projection, 83 …… Center hole, 85 …… Pin.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshiharu Saito 4-3-1, Tsunashima-higashi, Kohoku-ku, Yokohama-shi, Kanagawa Matsushita Communication Industrial Co., Ltd. (72) Inventor Hideki Matsumoto 4 Tsunashima-higashi, Kohoku-ku, Yokohama-shi, Kanagawa 3-3-1 Matsushita Communication Industrial Co., Ltd. (56) Reference JP-A-2-93370 (JP, A) JP-A-49-125076 (JP, A)

Claims (1)

[Claims] 1. An insulative housing having an opening on its upper surface, a metal shield case which includes the inner wall surface of the opening of the housing and has a shape with an open upper surface, and which is fixed to the inner wall surface. A resin base fixed inside the metal shield case, a sub-base integrally molded to this base, a diaphragm whose central part is fixed to the sub-base, and both front and back surfaces of this diaphragm. , Two piezoelectric ceramic elements having positive and negative electrodes opposed to each other and being conductively bonded, lead terminals respectively connected to the respective electrodes of these piezoelectric ceramic elements, and amplification of a signal output through these lead terminals. And a circuit board for filtering, and a metal upper plate that covers the opening of the metal shield case, and the piezoelectric ceramic element and the metal shield case and the upper plate. An acceleration sensor formed by shielding the serial circuit board from the outside.