JPH0611518A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To make it possible to output a stable signal even when the ambient temperature changes and to detect acceleration with high precision. CONSTITUTION:An inertia rod 2 is fitted swingably in a bottomed tubular casing 1 with support pins 3 interposed, and a piezoelectric body 4 formed of a d15 element is pressed, with an initial load, onto a contact part 2B of the inertia rod 2 by a pressing part 5B of a presser member 5. The acceleration at the time when the inertia rod 2 swings in directions A and B indicated by arrows in relation to the casing 1 is detected from a signal outputted from the piezoelectric body 4, through a contact plate 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor which is provided, for example, in a vehicle and is preferably used for detecting acceleration in the front-rear direction or the left-right direction.

[0002]

2. Description of the Related Art Generally, in an active suspension control device or the like provided in a vehicle, an acceleration sensor detects an acceleration in a front-rear direction or a left-right direction that acts when the vehicle is running, and the suspension is "hard" or "according to the acceleration". The attitude of the vehicle is controlled by adjusting it to "soft" to improve the riding comfort and steering stability of the vehicle.

As an acceleration sensor used in this type of prior art, a piezoelectric body called a so-called d ₃₃ element, in which the polarization axis and the signal axis are formed in the same direction, is provided in the casing, and the vehicle travels. When acceleration is applied in the front-rear direction or the left-right direction, the inertial body is displaced in response to the acceleration, thereby causing a load in the compression or tension direction to act on the piezoelectric body, and an electric signal output from the piezoelectric body. There is known a piezoelectric acceleration sensor which detects acceleration based on the above.

[0004]

By the way, in the above-mentioned prior art, since the piezoelectric body composed of the so-called d ₃₃ element is used, pyroelectricity is apt to occur due to the change of the ambient temperature, and the zero point is generated by the electric charge generated at this time. Fluctuates, and it is difficult to accurately detect and stabilize the acceleration.

As another conventional technique, a strain gauge type acceleration sensor using a strain gauge is also known. In this case, however, the acceleration detection sensitivity is low and it is necessary to form a bridge circuit. However, there is a problem that the entire sensor becomes large and it is difficult to make it small, and the heat resistance is low.

The present invention has been made in view of the above-mentioned problems of the prior art. The present invention can output a stable signal even with changes in ambient temperature, can detect acceleration with high accuracy, and is compact as a whole. It is an object of the present invention to provide an acceleration sensor that can be formed into a compact size and can be miniaturized.

[0007]

In order to solve the above-mentioned problems, the present invention relates to a cylindrical casing, an axially extending inside of the casing, which is swingably attached to the casing, and one end side of which is heavy. It consists of an inertia rod, which is a weight portion, and a d ₁₅ element, which is disposed in the casing so as to abut against the other end side of the inertia rod and in which a pair of electrodes are formed facing each other in the radial direction of the casing. A piezoelectric body, a pressing member which is provided in the casing so as to sandwich the piezoelectric body between the piezoelectric body and the inertial rod, and which applies an initial load in the axial direction to the piezoelectric body, and one electrode of the piezoelectric body. A conductive connecting member that is connected and grounds the one electrode to the casing side, and is connected to the other electrode of the piezoelectric body. Electrical signal output It adopts a configuration comprising a conductive contact plate to be led to the outside.

[0008]

With the above structure, the external force acts on the casing.
When the inertia rod swings back and forth or left and right
And d₁₅The piezoelectric body consisting of the element is pressed against the other end of the inertia rod.
The external force in the axial direction of the casing
Since it receives a shearing force,
A signal is generated between the radial electrodes and the electrical signal is
The external force is applied by removing it from the tact plate.
Can detect speed. Also, d ₁₅A piezoelectric body consisting of elements is
Piping due to temperature changes is made between the radial electrodes that are in the direction of the axis.
It is possible to prevent electricity from being generated.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

In the figure, reference numeral 1 denotes a casing which constitutes the main body of the acceleration sensor. The casing 1 is formed of a metal material such as stainless steel in a cylindrical shape with a bottom, and a cylindrical portion 1A extending in the axial direction and the cylindrical portion 1A. A bottom portion 1B that closes the lower end side of the portion 1A, a tubular step portion 1C that is located on the upper end side of the tubular portion 1A and has a smaller diameter than the tubular portion 1A, and a connector 9 described later is integrally molded, For example, four positioning holes 1D, 1D, ..., which are provided in the middle of the longitudinal direction of the portion 1A in the circumferential direction at predetermined intervals in the circumferential direction, and the outer periphery of the lower end side of the tubular portion 1A, are formed. It is generally composed of a male screw portion 1E as a mounting portion to be screwed to a vehicle body (not shown) or the like. Further, a cylindrical step portion 1C is provided on the upper end side of the cylindrical portion 1A.
Located on the lower side of, for example, three caulking parts 1F, 1F,
.. are formed at predetermined intervals in the circumferential direction as shown in FIG. 2, and each caulking portion 1F caulks and fixes a pressing member 5 described later in the casing 1.

Reference numeral 2 denotes an inertial rod that is swingably disposed in the casing 1. The inertial rod 2 is formed of a metal material such as brass as a stepped columnar rod and is connected to a piezoelectric body 4 which will be described later. A contact portion 2B having a concave portion 2A on the left side in FIG. 1 so that the contact surface has a semi-circular shape, and the contact portion 2B are integrally formed below the contact portion 2B and have a predetermined concave curved shape. A reduced diameter portion 2C having a reduced diameter, and a weight portion 2D having a spherical end surface extending downward from the lower end of the reduced diameter portion 2C and extending in a taper shape. Has been done.

Reference numerals 3, 3, ... Show support pins that swingably support the inertia rod 2 in the cylindrical portion 1A of the casing 1, and the support pins 3 are press-fitted into the positioning holes 1D of the casing 1. The tip portion 3A protruding into the casing is formed in a hemispherical shape with a curvature smaller than that of the reduced diameter portion 2C of the inertia rod 2. Each of the support pins 3 has a hemispherical tip portion 3A in front of the reduced diameter portion 2C of the inertia rod 2,
After that, the inertia rod 2 is swingably supported in the casing 1 in the front-rear direction, the left-right direction, and the like by making point contact from the left and the right.

Reference numeral 4 denotes a piezoelectric body disposed on the abutting portion 2B of the inertia rod 2 and disposed inside the casing 1. The piezoelectric body 4 has a piezoelectric property such as lead titanate as shown in FIG. The material is formed into a rectangular parallelepiped or a cube, and a predetermined high electric field is applied during manufacturing, so that the directions of spontaneous polarization are aligned and the polarization axis P and the stress axis F are oriented in the axial direction of the casing 1 and the signal axis V. Is formed as a so-called d ₁₅ element in the radial direction of the casing 1. In addition, the piezoelectric body 4
A pair of electrodes 4A and 4B are formed on the left and right side surfaces of the casing 1 so as to face each other in the radial direction of the casing 1 by means such as vapor deposition. The electrodes 4A and 4B are connected to a contact plate 7 and a connecting plate 6 which will be described later. Has been done.

Here, the upper and lower surfaces of the piezoelectric body 4 are pressed together by a pressing portion 5B of a pressing member 5 and an abutting portion 2 of the inertia rod 2 which will be described later.
It is sandwiched between B and B, and the corresponding contact portion 2B is in contact with the lower surface of the piezoelectric body 4 at the right side portion as shown by the dotted line in FIG. As shown in FIG. 4, when the inertia rod 2 swings in the directions A and B of the arrow (for example, the front-rear direction of the vehicle), the piezoelectric body 4 is placed between the contact portion 2B and the pressing portion 5B. A shearing force is applied in the direction of the stress axis F, and a detection signal as an electric signal corresponding to this shearing force is output as shown in FIG.

Reference numeral 5 denotes a holding member provided in the casing 1 so as to sandwich the piezoelectric body 4 with the inertia rod 2. The holding member 5 is a short stepped circle made of a metal material having a relatively large specific gravity. It is formed in a columnar shape, and an annular groove 5A is formed on the outer peripheral surface at the intermediate portion in the axial direction as shown in FIG. A pressing portion 5B projects downward at a predetermined inclination angle from the lower end side of the pressing member 5, and the lower end surface of the pressing portion 5B has a semicircular shape as shown by a dotted line in FIG. The upper surface is in contact with the left side portion in FIG.

Further, an axial through hole 5C is formed in the pressing member 5 so as to contact the outer peripheral surface at the position of the pressing portion 5B, and a contact plate 7 to be described later has an insulating tube 8 in the through hole 5C. It is inserted with. Then, the pressing member 5 is inserted into the casing 1 to apply an initial load in the axial direction to the piezoelectric body 4 by the pressing portion 5B, and each caulking portion 1F of the casing 1 is annularly formed by using a means such as three-point caulking. By engaging the groove 5A as shown in FIG. 2, it is positioned in the casing 1 in the axial direction and the radial direction.

Reference numeral 6 denotes a connecting plate as a connecting member for grounding one electrode 4B of the piezoelectric body 4 to the cylindrical portion 1A side of the casing 1. The connecting plate 6 is formed by pressing a conductive metal plate. 4, the piezoelectric body 4 is formed on the upper side.
Is a hooking portion 6A that is bent in an L-shape in cross section so as to be hooked on the upper surface of the above, and the lower side is an arcuate contact portion 6B that comes into surface contact with the inner peripheral surface of the cylindrical portion 1A. A connecting portion 6C is formed on the connecting plate 6 between the latching portion 6A and the arcuate contact portion 6B by bending in a substantially V-shape, and the connecting portion 6C has the arcuate contact portion 6B as the cylindrical portion. By making surface contact with the inner peripheral surface of 1A,
It is pressed against the electrode 4B of the piezoelectric body 4 with a spring property.

Reference numeral 7 denotes a contact plate connected to the electrode 4A of the piezoelectric body 4. The contact plate 7 is formed by press-molding a conductive metal rod, the lower end side of which is attached to the lower surface of the piezoelectric body 4. It is a hooking portion 7A that is bent in a substantially L-shape to be stopped. Further, the upper end side of the contact plate 7 becomes a terminal pin 7B protruding into the connector 9, and the terminal pin 7B is connected to an external wiring (not shown) or the like via the connector 9. Then, the contact plate 7 is brought into surface contact with the electrode 4A of the piezoelectric body 4 as shown in FIG. 3, whereby the detection signal from the piezoelectric body 4 is led to the outside.

Reference numeral 8 denotes an insulating tube covering the contact plate 7. The insulating tube 8 is made of a fluororesin or the like in a cylindrical shape, and the contact portion of the contact plate 7 with respect to the electrode 4A of the piezoelectric body 4 and the terminal pin 7B are provided. Except for this, it covers the outer periphery of the contact plate 7. Also,
A concave portion 2 of the inertia rod 2 is provided on the lower end side of the insulating tube 8.
A thick-walled portion 8A, which is inserted with a tightening allowance, is integrally formed in A, and the inertial rod 2 of the thick-walled portion 8A is indicated by arrows A and B in FIG.
When swinging in the direction, the hook 7A of the contact plate 7 is elastically deformed in the concave portion 2A and is constantly pressed toward the lower surface of the piezoelectric body 4. The insulating tube 8 is inserted into the through hole 5C of the pressing member 5 together with the contact plate 7 to insulate the contact plate 7 from the casing 1, the inertia rod 2 and the pressing member 5.

Further, reference numeral 9 denotes a connector provided on the upper end side of the casing 1. The connector 9 is integrally molded with the cylindrical step portion 1C of the casing 1 by an insulating resin material,
After the inertia rod 2, the piezoelectric body 4, the pressing member 5 and the like are loaded in the casing 1, the upper end side of the casing 1 is air-tightly and liquid-tightly closed. The connector 9 is formed in a cylindrical shape with a bottom, and a mating connector (not shown) is fitted on the inner peripheral side to connect the terminal pin 7B to the external wiring.

The acceleration sensor according to this embodiment has the above-mentioned structure, and its operation will be described below.

First, the male screw portion 1E of the casing 1 is screwed onto the body of the vehicle, and the inertia rod 2 in the casing 1 is screwed.
So that it sways in the directions A and B in the front-rear direction of the vehicle,
Mount the casing 1 on the vehicle. When acceleration is applied to the casing 1 via the body of the vehicle at the time of starting or accelerating the vehicle, for example, the weight portion 2D of the inertia rod 2 swings in the arrow B direction. Contact part 2B
Presses the lower surface of the piezoelectric body 4 in the direction of the stress axis F, and applies an axial shearing force to the piezoelectric body 4 between the pressing member 5B of the holding member 5.

This causes shear strain in the piezoelectric body 4,
An electromotive force corresponding to the acceleration at this time is generated between the electrodes 4A and 4B, and this electromotive force is output to the outside from the contact plate 7 as a detection signal as shown in FIG. Then, this detection signal increases as shown in FIG. 5 corresponding to the acceleration applied when the vehicle starts or accelerates, so that the acceleration can be detected based on the voltage value of the detection signal or the like.

When a deceleration as a negative acceleration acts during braking or deceleration of the vehicle, for example, the weight portion 2D of the inertia rod 2 swings in the direction of arrow A, so that the inertia rod 2 The contact portion 2B is driven so as to reduce the initial load applied by the pressing member 5, so that the shearing force applied in advance to the piezoelectric body 4 between the pressing member 5B and the pressing portion 5B is weakened according to the deceleration. Become. As a result, the detection signal output from the piezoelectric body 4 decreases corresponding to the deceleration as shown in FIG. 5, so that the deceleration can be detected as a negative acceleration based on the voltage value of this detection signal.

Further, as shown in FIG. 4, the piezoelectric body 4 has a so-called d direction in which the signal axis V is different from the polarization axis P and the stress axis F.
Since it is composed of ₁₅ elements, even if pyroelectricity is generated in the direction of the polarization axis P due to a change in ambient temperature, it is possible to effectively prevent the pyroelectricity from being weighted on the signal axis V, and It is possible to prevent the detection signal of 1 from changing due to a change in ambient temperature.

Therefore, according to this embodiment, a stable detection signal can be output from the piezoelectric body 4 even when the ambient temperature changes, and the longitudinal acceleration acting on the vehicle can be detected with high accuracy.

Further, the piezoelectric body 4 composed of the d ₁₅ element is sandwiched between the contact portion 2B of the inertia rod 2 and the pressing portion 5B of the pressing member 5 so as to apply a shearing force in the axial direction of the casing 1, and Since the contact plate 7 and the connection plate 6 are brought into contact with the left and right electrodes 4A and 4B from the radial direction of the casing 1, the piezoelectric body 4 is provided inside the casing 1.
Etc. can be accommodated compactly, and the whole can be miniaturized, and various effects are exhibited.

In the above embodiment, when the inertial rod 2 swings in the casing 1 in the directions A and B, the acceleration signal in the longitudinal direction of the vehicle is detected by the detection signal from the piezoelectric body 4. As described above, if the casing 1 is attached to the body of the vehicle or the like so that the swinging direction of the inertia rod 2 (directions indicated by arrows A and B) is in the left-right direction of the vehicle, steering of the vehicle is not possible. The acceleration in the left-right direction acting on the above can be detected by the detection signal from the piezoelectric body 4.

Although the inertia rod 2 is swingably mounted in the casing 1 by using the four support pins 3, 3, ... In the above embodiment, the present invention is not limited to this. For example, three support pins 3, 3, ... Are attached at a predetermined interval in the circumferential direction of the casing 1, and each support pin 3
Therefore, the inertia rod 2 may be swingably supported in the casing 1. On the other hand, the number of crimp portions 1F provided on the casing 1 is not limited to three and may be four or more.

[0030]

As described above in detail, according to the present invention, a piezoelectric body composed of d ₁₅ element is disposed between the inertia rod and the pressing member in the cylindrical casing, and the piezoelectric body is provided with the piezoelectric body. An initial load is applied in the axial direction between the inertia rod and the pressing member, and when the inertia rod swings with respect to the casing, an electric signal corresponding to the acceleration at this time is output from the piezoelectric body. Therefore, a stable electric signal can be output from the piezoelectric body even with changes in ambient temperature, acceleration can be detected with high accuracy, and the inertia rod and the piezoelectric body can be housed in the casing 1 in a compact manner. Can be converted.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an acceleration sensor according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view taken along line II-II in FIG.

FIG. 3 is an enlarged sectional view taken along the line III-III in FIG.

FIG. 4 is a vertical cross-sectional view showing an enlarged main part in FIG.

FIG. 5 is a characteristic diagram showing a relationship between acceleration and a detection signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Casing 2 Inertial rod 2A Recessed part 2B Abutting part 2C Reduced diameter part 2D Weight part 3 Support pin 4 Piezoelectric body 4A, 4B Electrode 5 Holding member 5B Pressing part 6 Connection plate (connecting member) 7 Contact plate 7B Terminal pin 8 Insulation tube 8A Thick part 9 Connector F Stress axis P Polarization axis V Signal axis

Claims (1)

[Claims] 1. A cylindrical casing, an inertia rod extending axially in the casing and swingably attached to the casing, one end of which is a weight portion, and the other end of the inertia rod. A piezoelectric body composed of a d ₁₅ element, which is disposed in the casing so as to abut on the casing, and has a pair of electrodes facing each other in the radial direction of the casing, and the piezoelectric body is sandwiched between the piezoelectric rod and the inertia rod. So as to provide an initial load in the axial direction to the piezoelectric body and a conductive member that is connected to one electrode of the piezoelectric body and grounds the one electrode to the casing side. And a conductive contact plate which is connected to the other electrode of the piezoelectric body and which, when the inertia rod swings with respect to the casing, guides an electric signal output from the piezoelectric body to the outside. From Acceleration sensor made up.