JP2003315443A - Ultrasonic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic sensor in a configuration where beauty is improved without reducing sensor performance. <P>SOLUTION: A gap is provided between a cylindrical sidewall 11b of an inner cylinder and a cylindrical sidewall 13b of an outer enclosure. The cylindrical sidewall 11b in the inner enclosure comes into contact with four projections being provided inside the cylindrical sidewall 13b of the outer enclosure for supporting. The support section supports a section that is half or less of the height of the cylindrical sidewall 11b at the side of an ultrasonic radiation wall 11a in the inner enclosure 11. Additionally, when a support angle in the support section at one point with the center of the cylindrical sidewall 11b in the inner enclosure is set to be a zero point 0 is set to α-δ, the sum α+β+γ+δ of the support angle becomes 180 degrees or less. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic sensor, and is suitable for application to a vehicle obstacle detection sensor, for example.

[0002]

2. Description of the Related Art Conventionally, as an ultrasonic sensor of this type, there is one disclosed in Japanese Patent Laid-Open No. 2001-16694. This ultrasonic sensor is provided on a bumper of a vehicle, transmits ultrasonic waves from the rear or corner of the vehicle, receives ultrasonic waves reflected by an obstacle, and detects the obstacle.

A front view of a conventional ultrasonic sensor is shown in FIG.
Shown in. Further, FIG. 14B shows a cross-sectional view taken along the line AA 'in the front view. As shown in FIGS. 14A and 14B, the ultrasonic sensor includes a piezoelectric vibrating element 10 and an inner casing 1.
1, the vibration absorber 12, the outer casing 13, the sponge 14, and the vibration absorber 15.

The piezoelectric vibrating element 10 is fixed to the inner bottom portion of the inner casing 11, that is, the bottom portion of the hollow portion formed by the plate-shaped bottom portion as the ultrasonic wave radiation wall 11a and the cylindrical side wall 11b. . The cylindrical side wall 11b of the inner casing 11
A vibration absorber 12 made of rubber or the like is provided between the outer wall of the outer casing and the inner wall of the cylindrical side wall 13b of the outer casing 13, and the inner casing 11 is
The vibration is insulated from the outer casing 13 through the vibration absorber 12 and is supported on the entire circumference. Further, the cylindrical side wall 13b of the outer casing 13 is fitted in a hole provided in the bumper. In this way, by vibration-insulating the inner casing 11 and the outer casing 13 with the vibration absorber 12 such as rubber,
The vibration of the ultrasonic wave radiating wall of the inner casing is suppressed from being transmitted to the bumper.

[0005]

In the ultrasonic sensor described above, the outer casing 13 supports the inner casing 11 by the vibration absorber 12 such as rubber over the entire circumference. However, since it is difficult to paint the vibration absorber 12 such as rubber, the vibration absorber 12 is conspicuous when mounted on the bumper 16 and spoils the aesthetic appearance.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an ultrasonic sensor having a structure improved in aesthetics without deteriorating the sensor performance.

[0007]

In order to achieve the above object, in the invention described in claim 1, the inner casing (11) is provided with a plurality of outer casings (13) on the ultrasonic radiation wall (11a) side. It is supported at supporting points, and a gap is provided between the outer wall of the cylindrical side wall (11b) of the inner housing (11) and the inner wall of the cylindrical side wall (13b) of the outer housing (13) except at those supporting points. It is characterized by that.

According to this feature, there is a portion that is not constrained by the cylindrical side wall (13b) of the outer casing (13), and that portion can vibrate, so that the inner casing vibrates in combination with this vibration. It is possible to suppress a decrease in vibration of the ultrasonic vibration wall (11a) of the body (11). Therefore, it is possible to obtain the same sensor performance as that of the conventional one supported through the vibration absorber (12). Further, as described above, it is possible to eliminate the need for the vibration absorber (12) by supporting at a plurality of supporting points and forming the gaps. Further, as in the invention according to claim 5, it is possible to form the gaps. Vibration absorber (1
Even when 2) is provided, since the area of the portion where the vibration absorber (12) is exposed to the outside can be made smaller than that of the conventional one, the aesthetic appearance can be improved more than that of the conventional one.

The invention according to claim 1 can be more specifically configured by the inventions according to claims 2 to 4. That is, in the invention described in claim 2, the height at which the outer casing (13) supports the inner casing (11) is equal to or less than half the height of the inner casing (11).
With the center of the cylindrical side wall (11b) of 1) as the origin (O), the sum of the support angles of the support points is 180 degrees or less.

According to the third aspect of the invention, the height at which the outer casing (13) supports the inner casing (11) is larger than half the height of the inner casing (11). The cylindrical side wall (11b) of the inner housing (11) is cylindrical, the outer housing (13) supports the inner housing (11) at eight locations or less, and the inner housing (11) is further cylindrical. With the center of the side wall (11b) as the origin (O), the support angle of each support location is 10 degrees or less.

According to the fourth aspect of the invention, the height at which the outer casing (13) supports the inner casing (11) is larger than half the height of the inner casing (11). The cylindrical side wall (11b) of the inner housing (11) is an ultrasonic radiation wall (11b).
The section parallel to a) has a polygonal shape, and the outer housing (13) supports the inner housing (11) at a position of not more than twice the number of corners of the polygon, and further, the inner housing (11). Tubular side wall (11
With the center of b) as the origin (O), the support angle of each support location is 10 degrees or less.

The reference numerals in parentheses of the above means indicate the correspondence with the specific means described in the embodiments described later.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) FIG. 1A shows a front view of an ultrasonic sensor according to an embodiment of the present invention.
A cross-sectional view taken along the line AAA 'of this front view is shown in FIG. As shown in FIGS. 1A and 1B, the ultrasonic sensor includes a piezoelectric vibrating element 10, an inner casing 11, and a vibration absorber 1.
2, outer casing 13, sponge 14 and vibration absorber 15
It consists of The inner casing 11 is made of aluminum, and the outer casing 13 is made of resin.

The piezoelectric vibrating element 10 is bonded to the inner bottom portion of the inner casing 11, that is, the bottom portion of the hollow portion formed by the plate-shaped bottom portion as the ultrasonic wave radiation wall 11a and the cylindrical side wall 11b. .

The cylindrical side wall 11b of the inner casing 11 comes into contact with four convex portions (supporting parts) a, b, c, d provided inside the cylindrical side wall 13b of the outer casing 13, and is supported there. A gap is formed between the cylindrical side wall 11b of the inner housing 11 and the cylindrical side wall 13b of the outer housing 13 except at the supporting position. The height H of the supporting portion of the outer casing 13 on the side of the ultrasonic radiation wall 11 a is determined by the height H of the cylindrical side wall 11 of the inner casing.
It is not more than half the height L of b (H ≦ L / 2).

In the above structure, since a gap is provided between the outer wall of the first cylindrical side wall 11b of the inner casing 11 and the inner side of the second cylindrical side wall 13b of the outer casing 13,
A portion that is not restrained by the first cylindrical side wall 13b is formed, and that portion can vibrate, and a reduction in vibration of the ultrasonic vibration wall 11a of the inner housing 11 that vibrates in combination with this vibration is suppressed. be able to.

When the support angle of one support portion with the center of the cylindrical side wall 11b as the origin O is α to δ, the sum of the support angles α + β + γ + δ is 180 degrees or less. When the sum of the support angles α + β + γ + δ is large, the inner casing 1
Since the part that constrains 1 becomes large, the ultrasonic wave radiation wall 11
The displacement of a decreases, the damping coefficient increases, and the performance of the sensor deteriorates. Therefore, the sum of the support angles α + β + γ + δ is preferably 180 degrees or less, which corresponds to ½ of the entire circumference of 360 degrees.

Further, in the above-mentioned structure, the outer wall of the cylindrical side wall 11b of the inner casing 11 and the outer casing 13 are the same as in the prior art.
Between the inner wall of the cylindrical side wall 13b of the vibration absorber 12 such as rubber.
Is fitted. As described above, the vibration isolation can be effectively performed by providing the vibration absorber 12, but it is also possible not to fit the vibration absorber 12 as described later.

The inner casing 11 and the outer casing 13 can be fixed by press fitting, bonding, screwing, casting, welding, fitting.

The vibration absorber 15 is provided to absorb mechanical vibration (reverberation) generated by the inner casing 11 during transmission of ultrasonic waves, and the sponge 14 is provided with ultrasonic waves of the received ultrasonic waves. It is provided to prevent reflection on the radiation wall 11a.

2A and 2B show vibration modes of the cylindrical casing. As shown in FIG. 2A, when the tubular side wall 11b of the tubular housing is displaced outward from the center of the cylinder, the ultrasonic wave radiation wall 11a is displaced toward the opening. Also, FIG.
As shown in (b), when the tubular side wall 11b of the tubular housing is displaced toward the center of the cylinder, the ultrasonic radiation wall 11a is displaced in the direction opposite to the opening. In this way, the tubular side wall 11b and the ultrasonic radiation wall 11a are coupled and vibrate, and the displacement of the tubular side wall 11b increases as the distance from the ultrasonic radiation wall 11a increases.
Therefore, the ultrasonic radiation wall 1 with a small displacement of the cylindrical side wall 11b
By supporting the 1a side, it is possible to suppress a decrease in vibration of the ultrasonic radiation wall 11a.

As described above, the outer wall of the first tubular side wall 11b of the inner housing 11 and the second tubular side wall 1 of the outer housing 13 are arranged.
By providing a gap between the inner side of 3b and the inside of 3b, there is a portion that is not restrained by the first cylindrical side wall 13b, and that portion can vibrate. And the first tubular side wall 1
By supporting the side of the ultrasonic wave radiating wall 11a having a small displacement of 1b, it is possible to suppress the reduction of the vibration of the ultrasonic wave oscillating wall 11a of the inner casing 11 that vibrates in combination with this vibration, and to suppress the vibration. The same sensor performance as when supported via 12 is obtained.

The ultrasonic sensor has a resonance frequency, and the resonance frequency depends on the driving frequency of the piezoelectric vibrating element, the shape and material of the vibrating housing, the shape of the piezoelectric vibrating element, and the like. In many ultrasonic sensors used in vehicles, both the resonance frequency and the driving frequency of the piezoelectric vibrating element are about 40 kHz. The vibration mode differs depending on the relationship between the resonance frequency and the driving frequency of the piezoelectric vibration element,
The drive frequency of the piezoelectric vibration element is 40 kHz, 80 kHz,
In the case of 120 kHz, the vibration modes are the primary, secondary and tertiary modes.

FIGS. 3A to 3C show vibration modes of the side wall of the cylindrical casing. FIG. 3A is a primary mode, FIG.
Represents the secondary mode, and (c) represents the tertiary mode. As shown in the figure, the number of vibration nodes varies depending on the vibration mode. The vibration node is the displacement (amplitude) on the vibration surface.
At the point where is zero, there are 4, 6, and 8 vibration nodes in the order of the primary, secondary, and tertiary modes. Therefore, in FIG. 1, when the cylindrical side wall 13b of the outer casing supports the cylindrical side wall 11b of the inner casing, there are four locations in the primary mode, six locations in the secondary mode, and eight locations in the tertiary mode. For example, it is effective to select a supporting point according to the driving frequency of the piezoelectric vibration element, such as a point.

Further, the resonance frequency band in the conventional ultrasonic sensor is about 50 kHz, and in this case, the driving frequency of the piezoelectric vibrating element in which the vibration mode is the third mode is 15
It becomes about 0 kHz. However, the driving frequency of a piezoelectric vibration element that is normally used is about 20 kHz to 70 kHz, and the received signal becomes weaker as the order of the vibration mode becomes higher, so that it is normally used in the vibration mode of the third order or lower. Therefore, the cylindrical side wall 13b of the outer casing may support the cylindrical side wall 11b of the inner casing at eight locations or less.

(Second Embodiment) FIG. 4A shows a front view of an ultrasonic sensor according to a second embodiment. Further, a cross-sectional view taken along the line AAA 'of this front view is shown in FIG. Figure 4
As shown in (a) and (b), the cylindrical side wall 13 of the outer housing is formed.
b and the cylindrical side wall 11b of the inner casing are cylindrical and arranged coaxially. The outer casing 13 supports the inner casing 11 at four convex portions a, b, c, d, and the supporting angles α, β, γ of the respective supporting portions with the center of the cylindrical side wall 11b as the origin O.
Each δ is 10 degrees or less. Further, the height H of the support portion of the outer casing 13 on the ultrasonic radiation wall 11a side is larger than half the height L of the cylindrical side wall 11b of the inner casing 11 (H> L / 2). Here, the vibration mode is a primary mode, and the number of vibration nodes is four, and since it is supported at the same four positions as the number of vibration nodes, the sensor performance ideally does not deteriorate. However, if the supporting portion deviates from the node of vibration, the portion having a large displacement away from the ultrasonic wave radiation wall 11a is constrained, and the sensor performance deteriorates. Therefore,
It is desirable that the supporting angles α to δ at each supporting portion are small, and each is 10 degrees or less.

Although the ultrasonic sensor has a circular cross section parallel to the ultrasonic radiation wall 11a of the inner casing,
The shape is not limited to a circle, and may be, for example, a polygon or an ellipse. In the case of a polygon, the number of nodes of vibration in modes of the third order and lower is less than or equal to twice the number of corners, and it is sufficient to support the nodes at a position equal to or less than twice the number of corners. In essence, the number of vibration nodes corresponding to each shape or twice as many supporting points may be used for supporting.

5 (a) and 5 (b) show the maximum displacement and damping coefficient of the vibration characteristics of the ultrasonic radiation wall due to the difference in the supporting conditions (a) to (d) between the inner casing 11 and the outer casing 13. Show. The supporting conditions (a) to (d) are shown in FIGS. 6 to 9.

6 (a) and 6 (b) are a front view of the supporting condition (a) and a sectional view taken along the line AAA 'in the front view. The support condition (a) is that the outer casing 13 is made of rubber with the inner casing 1
This is the case of supporting 1.

A front view of the supporting condition (b) and a cross-sectional view taken along the line AAA 'in the front view are shown in FIGS. 7 (a) and 7 (b). As shown in the figure, the support condition (b) is a case where the outer housing 13 supports the inner housing 11 over the entire surface.

8 (a) and 8 (b) show a front view of the supporting condition (c) and a cross-sectional view taken along the line AA-A 'in the front view. As shown in the figure, the support condition (C) is a case where the outer housing 13 supports the inner housing 11 around the entire circumference on the ultrasonic wave radiation wall side only.

9 (a) and 9 (b) show a front view of the supporting condition (d) and a sectional view taken along the line AA-A 'in the front view. As shown in the figure, the support condition (d) is a case where the outer housing 13 is supported by a part of the inner housing 11 on the ultrasonic wave radiation wall side with a gap. The vibration absorber 12 is not fitted.

When the outer casing 13 supports the inner casing 11 over the entire surface as in the structure shown in the condition (b),
Both the maximum displacement and damping coefficient decrease compared to the case of rubber support shown in condition (a). When the outer casing 13 supports the inner casing 11 on the entire circumference only on the ultrasonic wave emitting wall side as in the structure shown in the condition (C), the condition (A)
The maximum displacement is increased, but the damping coefficient is decreased, compared with the case of the rubber support shown in Fig. In any of the conditions, the sensor performance is lower than that in the case of supporting by the rubber shown in the condition (a).

In FIG. 5, as in the structure shown in the condition (d), the outer casing 13 is supported by a part of the inner casing 11 on the ultrasonic wave radiating wall side with a gap, and the vibration absorber 12 is supported. Even when the ultrasonic radiation wall 11a is not fitted, the maximum displacement and the damping coefficient of the ultrasonic radiation wall 11a are the same as those in the case of the rubber support shown in the condition (a). Therefore, the exposed portion of the vibration absorber 12 can be made inconspicuous. Furthermore, since the color matching between the bumper 16 and the inner casing becomes easy, the aesthetic appearance can be improved. Further, the number of assembling points can be reduced.

In FIG. 10, the cylindrical side wall 11b of the inner casing and the cylindrical side wall 13b of the outer casing are supported only on the ultrasonic wave radiating wall 11a side with a gap, and four supporting portions are provided. It is a figure which shows the structure at the time of making a support angle 0 degree. Under such conditions, the supporting height H = L / 9, H
The maximum displacement and the attenuation coefficient of the ultrasonic radiation wall 11a in the case of = 2L / 9 are shown in FIGS. 11 (a) and 11 (b), respectively. The maximum displacement and the damping coefficient shown in the figure are characteristics with respect to changes in the supporting load from the four supporting portions on the outer casing 13 side toward the center of the cylindrical side wall 11b of the inner casing.

In FIGS. 11 (a) and 11 (b), when the support height H = L / 9, neither the maximum displacement nor the damping coefficient significantly changes with respect to the support load. However, when the support height H = 2L / 9, the ultrasonic radiation wall 1 with respect to the support weight is
The displacement of 1a and the change of the damping coefficient become large. In particular,
Since the attenuation coefficient is reduced, that is, the mechanical vibration (reverberation) time generated during ultrasonic wave transmission is lengthened. Then, the ultrasonic waves reflected from the obstacles at a short distance overlap with the reverberation, so that the obstacles at a short distance cannot be detected and the sensor performance deteriorates. Therefore, it can be seen that the shorter the support height H is, the smaller the influence of the change in the support weight on the maximum displacement and the damping coefficient due to the change in the support weight, and the better the sensor performance.

In FIG. 12, the cylindrical side wall 11b of the inner casing and the cylindrical side wall 13b of the outer casing are supported only on the ultrasonic wave radiating wall side with a gap therebetween, and the supporting portions are provided at four locations and are supported respectively. It is a figure which shows the structure in case height H = L / 9.
In such a structure, the sum of the support angles α + β + γ + δ
The maximum displacement and damping coefficient for
It shows in (b). In the figure, the cylindrical side wall 11b of the inner casing is shown.
And the sum of the support angles of the tubular side wall 13b of the outer housing α + β +
When γ + δ becomes large, the portion that restrains the inner casing 11 becomes large, so that the displacement of the ultrasonic radiation wall 11a decreases. Then, due to the decrease in displacement of the ultrasonic radiation wall 11a,
The transmitted sound pressure is reduced, which leads to deterioration of sensor performance. Therefore, the sum of the support angles of the inner casing 11 and the outer casing 13 α + β
The smaller + γ + δ is desirable.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an ultrasonic sensor to which a first embodiment of the present invention is applied.

FIG. 2 is a diagram showing a general vibration mode of a cylindrical casing.

FIG. 3 is a diagram showing a general vibration mode of a side wall of a cylindrical casing.

FIG. 4 is a diagram showing a modification of the ultrasonic sensor of the present invention.

FIG. 5 is a diagram showing the maximum displacement and the damping coefficient of the vibration characteristics of the ultrasonic radiation wall due to the difference in the support conditions of the inner casing and the outer casing.

6 is a diagram showing the structure of condition (a) in FIG.

FIG. 7 is a diagram showing a structure of condition (b) in FIG.

FIG. 8 is a diagram showing a structure of condition (c) in FIG.

9 is a diagram showing the structure of condition (d) in FIG.

10 is a diagram showing a structure of the ultrasonic sensor in FIG.

FIG. 11 is a diagram showing the maximum displacement and damping coefficient of the vibration characteristics of the ultrasonic radiation wall due to the difference in support height between the inner casing and the outer casing.

12 is a diagram showing a structure of the ultrasonic sensor in FIG.

FIG. 13 is a diagram showing the maximum displacement and the damping coefficient when the sum of the support angles is changed.

FIG. 14 is a diagram showing a configuration of a conventional ultrasonic sensor.

[Explanation of symbols]

10 ... Piezoelectric vibrating element, 11 ... Inner casing, 11a ... Ultrasonic radiation wall, 11b ... Cylindrical side wall, 12 ... Vibration absorber,
13 ... Outer wall housing, 13b Cylindrical side wall, 14 ... Sponge,
15 ... Vibration absorber.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hisashi Matsuoka             14 Iwatani Shimohakaku-cho, Nishio-shi, Aichi Stock Association             Company Japan Auto Parts Research Institute (72) Inventor Yoshihisa Sato             1-1, Showa-cho, Kariya city, Aichi stock market             Inside the company DENSO (72) Inventor Takekazu Mawa             1-1, Showa-cho, Kariya city, Aichi stock market             Inside the company DENSO F-term (reference) 5D019 GG09                 5J083 AB13 AC19 AF09 CA01 CA14                       CA22 CA31 CB03 CB07

Claims (5)

[Claims] 1. An inner casing (1) having a piezoelectric vibrating element (10), a bottom surface part to which the piezoelectric vibrating element (10) is attached to form an ultrasonic wave emitting wall (11a), and a cylindrical side wall (11b). 11) and an outer casing (1) having a cylindrical side wall (13b) arranged coaxially with the cylindrical side wall (11b) of the inner casing (11).
3), the outer housing (13) supports the inner housing (11) at a plurality of support points on the ultrasonic wave emission wall (11a) side, and the support is provided at a position other than the plurality of support points. Inner housing (1
1) The outer wall of the cylindrical side wall (11b) and the outer casing (1)
An ultrasonic sensor having a gap formed between the inner wall of the cylindrical side wall (13b) of 3). 2. The height at which the outer housing (13) supports the inner housing (11) is not more than half the height of the inner housing (11), and the height of the inner housing (11) is smaller than that of the inner housing (11). The ultrasonic sensor according to claim 1, wherein the sum of the support angles of the respective support points is 180 degrees or less, with the center of the cylindrical side wall (11b) as the origin (O). 3. The height at which the outer housing (13) supports the inner housing (11) is larger than half the height of the inner housing (11). ) The cylindrical side wall (11b) of FIG.
Supports the inner casing (11) at eight locations or less,
The ultrasonic wave according to claim 1, wherein the center of the cylindrical side wall (11b) of the inner casing (11) is the origin (O), and the supporting angle of each supporting portion is 10 degrees or less. Sensor. 4. The height at which the outer housing (13) supports the inner housing (11) is larger than half the height of the inner housing (11). ), The cylindrical side wall (11b) has a polygonal cross section parallel to the ultrasonic wave radiating wall (11a), and the outer casing (13) defines the inner casing (11) with the number of corners of the polygon being two. It is supported at less than double times, and the supporting angle of each supporting point is 10 degrees or less with the center of the cylindrical side wall (11b) of the inner casing (11) as the origin (O). The ultrasonic sensor according to claim 1. 5. The ultrasonic sensor according to claim 1, wherein a vibration absorber (12) is fitted in the gap.