JP4768684B2 - Ultrasonic sensor - Google Patents

Description

  The present invention relates to an ultrasonic sensor used for detecting an obstacle in a vehicle.

Conventionally, as this kind of ultrasonic sensor, there exists a thing of the structure shown by patent document 1. FIG. This configuration is shown in FIG. As shown in FIG. 9, the ultrasonic sensor 21 has a piezoelectric vibrator 23 bonded to the inner surface of the bottom 22 a of a cylindrical bottomed casing 22. Further, a sponge 24 and silicon rubber 25 are provided inside the housing 22. In this ultrasonic sensor 21, a voltage signal is input to the piezoelectric vibrator 23 to be deformed (vibrated) at, for example, 70 to 40 kHz, and ultrasonic waves are transmitted from the outer surface of the bottom 22 a using the resonance of the casing 22. Then, the housing 22 receives the ultrasonic wave, deforms the piezoelectric vibrator 23, and outputs a voltage signal from the piezoelectric vibrator 23.
Japanese Patent Laid-Open No. 10-206529

  As shown in FIG. 10, the ultrasonic sensor 1 having the above-described conventional configuration is attached to a rear bumper 26 or the like of a vehicle. The sensor surface is exposed to the stay 26b through the rubber 27. And it is used for confirming the presence or absence of a rear obstacle when the vehicle moves backward.

However, the ultrasonic sensor 21 having the conventional configuration has a large width dimension (diameter dimension) H, looks large from the outside of the vehicle, has a poor design appearance, and has a high probability of being hit by foreign objects such as pebbles.
As a countermeasure, it is conceivable that the width dimension H of the housing 22 is simply reduced. However, if the housing 22 is simply reduced, the resonance frequency of the housing 22 is increased, and the attenuation of the ultrasonic wave is increased. It gets worse.

  On the other hand, if a measure is taken to make the thickness of the bottom 22a of the housing 22 extremely thin (for example, about 0.1 mm), the frequency can be reduced, but the strength of the housing 22 is lowered. Furthermore, there is a possibility that the bottom 22a may be bent, and there is a new problem that it is difficult to achieve adhesion in surface contact with the piezoelectric vibrator 23. That is, the actual situation is that the thickness of the bottom portion 22a to which the piezoelectric vibrator 23 is attached cannot be made very thin.

  The present invention has been made in view of the above circumstances, and its purpose is to reduce the size seen from the transmitting or receiving direction, to reduce the so-called sensor surface, and to increase the housing strength, It is an object of the present invention to provide an ultrasonic sensor capable of reliably bonding the surface of a piezoelectric vibrator and improving the design appearance when mounted on a vehicle.

According to the first aspect of the present invention, when the piezoelectric vibrator attached to the bottom inner surface of the bottomed casing is vibrated by applying an electric signal, the casing resonates, and the bottom, shaft, and surface of the casing are resonated. And vibrate synchronously. In this case, the surface portion acts as an ultrasonic wave transmission surface portion. Further, when an ultrasonic wave is transmitted (reflected) from the outside, it is received by the surface portion, and the piezoelectric vibrator of the housing is vibrated through the shaft portion to generate an electric signal. In this case, the surface portion functions as an ultrasonic wave receiving surface portion. The surface portion and the shaft portion are provided on the outer surface of the bottom portion of the casing so as to extend in a direction opposite to the piezoelectric vibrator, so that the casing portion including the piezoelectric vibrator is a spring, and the surface portion and the shaft Even if the portion becomes mass and the casing is reduced, the resonance frequency can be lowered without reducing the thickness of the bottom portion. Further, since the size of the surface portion only needs to be large enough to transmit or receive waves, it is not necessary to increase the size of the surface portion. In addition, the housing strength can be increased, the piezoelectric vibrator can be securely attached to the surface, and the design appearance when attached to the vehicle is improved.
In this case, the surface portion may be configured to be smaller than the bottom portion (invention of claim 2), and in this way, the surface portion can be further reduced and the design appearance when attached to the vehicle is further improved.

  In this case, the surface portion for transmitting or receiving the ultrasonic wave may have a shape having a different length in the two axial directions perpendicular to the surface portion (invention of claim 3). If it does in this way, there will be the following effects. That is, when an ultrasonic sensor is attached to a bumper of a vehicle and an obstacle is detected, it is desirable to widen the detection angle with one sensor in the horizontal direction, and in the vertical direction to prevent erroneous detection due to reflected waves from the road surface. It is desirable to set an appropriate detection angle. In this respect, according to the third aspect of the present invention, the directivity can be different (provide partial directivity) in the two perpendicular directions, and the detection angle in the horizontal direction is wider than that in the vertical direction. can do.

Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a longitudinal sectional shape of an ultrasonic sensor 1 according to the present invention, and FIG. 2 shows a shape seen from the front. 1 and 2, the ultrasonic sensor 1 includes a sensor body 2 and a piezoelectric vibrator (PZT) 3. The sensor body 2 is composed of, for example, an integrally formed body of aluminum, and integrally includes a housing 4, a shaft portion 5, and a surface portion 6.
The casing 4 has a cylindrical bottom shape, and has a bottom portion 4a on one end side and an opening 4b on the other end side. The bottom portion 4a of the casing 4 is a piezoelectric vibrator mounting portion, and the piezoelectric vibrator 3 is attached to the inner surface of the bottom portion 4a by adhesion in a surface contact state.

  The shaft portion 5 has a columnar shape that is smaller (smaller in diameter) than the bottom portion 4a, and extends in the direction opposite to the piezoelectric vibrator 3 (the direction opposite to the opening 4b) from the outer surface of the bottom portion 4a. Is formed. The surface portion 6 has a circular shape and is formed at the distal end portion of the shaft portion 5. This surface portion 6 transmits or receives ultrasonic waves. In this case, the size (diameter dimension) of the surface portion 6 a is substantially the same as the size (diameter dimension) of the bottom portion 4 a of the housing 4.

The housing 4 is filled with a sound absorbing material 7 such as sponge and a vibration absorber 8 such as silicon rubber. Further, lead wires 9 for the piezoelectric vibrator 3 are led out from the inside of the housing 4 to the outside.
As shown in FIG. 3, the ultrasonic sensor 1 having the above configuration is configured such that, for example, an outer surface (so-called sensor surface) of the surface portion 6 is exposed from an arrangement hole 10 a formed in a bumper 10 of a vehicle via a rubber 11 on a stay 10 b. It is attached. The ultrasonic sensor 1 is used to confirm the presence or absence of a rear obstacle when the vehicle is moving backward.

  In this embodiment, when the piezoelectric vibrator 3 attached to the inner surface of the bottom portion 4a of the housing 4 vibrates by applying an electric signal, the housing 4 resonates, and the bottom portion 4a and the shaft portion 5 of the housing 4 are resonated. In addition, the surface portion 6 vibrates synchronously. In this case, the surface part 6 acts as an ultrasonic wave transmission surface part. Further, when an ultrasonic wave is transmitted (reflected) from the outside, it is received by the surface portion 6 and the piezoelectric vibrator 3 of the housing 4 vibrates via the shaft portion 5 to generate an electric signal. In this case, the surface portion 6 acts as an ultrasonic wave receiving surface portion. Since the surface portion 6 and the shaft portion 5 are provided on the outer surface of the bottom portion 4a of the housing 4 so as to extend in a direction opposite to the piezoelectric vibrator 3, the housing 4 portion including the piezoelectric vibrator 3 is included. The surface portion 6 and the shaft portion 5 become mass, and even if the housing 4 is made small, the resonance frequency can be lowered without reducing the thickness of the bottom portion 4a. Further, the size of the surface portion 6 may be any size as long as it can be transmitted or received. Therefore, it is not necessary to increase the size, and generally, the size seen from the direction of transmission or reception can be reduced. It can be made small and the strength of the housing 4 can be increased. And since the bottom part 4a of the housing | casing 4 does not need to be so thin, the inner surface (attachment surface of the piezoelectric vibrator 3) of the bottom part 4a does not bend, and it is easy to process this inner surface into a flat surface. Also, the piezoelectric vibrator 3 can be securely attached to the surface. Furthermore, the design appearance when attached to a vehicle is improved.

FIGS. 4 to 6 show a second embodiment of the present invention. This second embodiment is different from the first embodiment in the following points.
A portion 5a on the distal end side of the shaft portion 5 is slightly thickened, and the distal end surface of this portion 5a is used as a surface portion 12 for ultrasonic wave transmission and reception. The surface portion 12 is configured to be smaller (smaller in diameter) than the bottom portion 4a of the housing 4. FIG. 6 shows the state of vibration of the ultrasonic sensor 1 of this embodiment as a result of eigenvalue analysis by FEM (Finite Element Method). The solid line in FIG. 6 indicates the original state, and the thin line indicates the deformed state.

  According to the second embodiment, the surface portion 12 can be further reduced, and the design appearance when attached to the vehicle is further improved. In particular, in the second embodiment, since the surface portion 12 can be made considerably small, for example, when two ultrasonic sensors 1 are arranged side by side, the distance between the surface portions 12 is shortened (for example, a separation distance of λ / 2, 40 kHz). In this case, since λ (wavelength) is 8.5 mm, λ / 2 can be 4.25 mm), and angle measurement can be performed based on a phase difference, thereby improving azimuth detection accuracy. By the way, in the conventional configuration, since the surface portion is in the casing and the size of the casing is large, the distance between the ultrasonic sensors can be set to “λ / 2” even if the ultrasonic sensors are arrayed. The distance between the ultrasonic sensors cannot be measured by the phase difference because the distance between the ultrasonic sensors is about “λ” or “2λ”.

7 to 8 show a third embodiment of the present invention. This third embodiment differs from the first embodiment in the following points.
A length L1 in the x direction and a length L2 in the y direction are different from each other in the two axial directions (x direction, y direction) of the surface portion 6 (L1 <L2).

  According to the third embodiment, it is possible to make the directivities different (provide partial directivity) in the x direction and the y direction. For example, when mounting on a bumper of a vehicle, the horizontal direction has a wide detection angle by attaching the x direction (short direction) to the horizontal direction and the y direction (longitudinal direction) to the vertical direction, and the vertical direction (road surface direction) is The detection angle can be narrowed.

The shape of the surface portion in the third embodiment is not particularly limited as long as the length in the biaxial direction is different, and may be rectangular, elliptical, or other shapes.
The present invention is not limited to the above-described embodiments, and may be modified as follows.
The housing and the shaft portion may be integrated by welding or the like. The sensor body (housing, shaft portion, surface portion) may be brass or the like in addition to aluminum. The surface portion 6 may be dedicated to ultrasonic transmission or reception.

1 is a longitudinal side view of an ultrasonic sensor showing a first embodiment of the present invention. Front view of ultrasonic sensor Longitudinal side view with ultrasonic sensor attached to vehicle bumper FIG. 1 equivalent view showing a second embodiment of the present invention. 3 equivalent figure Diagram showing the vibration of the ultrasonic sensor FIG. 1 equivalent view showing a third embodiment of the present invention 2 equivalent diagram 1 equivalent diagram showing a conventional example 3 equivalent figure

Explanation of symbols

  In the drawings, 1 is an ultrasonic sensor, 2 is a sensor body, 3 is a piezoelectric vibrator, 4 is a housing, 5 is a shaft portion, 6 is a surface portion, 10 is a bumper, and 12 is a surface portion.

Claims (3)

A bottomed housing;
A piezoelectric vibrator attached to the bottom inner surface of the housing;
A shaft portion provided in a form extending in the opposite direction to the piezoelectric vibrator on the outer surface of the bottom portion of the housing, and having a width smaller than the bottom portion,
An ultrasonic sensor comprising a surface portion that is provided at a tip portion of the shaft portion and transmits or receives ultrasonic waves.   The ultrasonic sensor according to claim 1, wherein the surface portion is smaller than the bottom portion.   The ultrasonic sensor according to claim 1, wherein the surface portion that transmits or receives the ultrasonic wave has a shape having different lengths in two orthogonal directions of the surface portion.

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