Abstract:
In an ultrasonic sensor having a case that is integrally constructed from tubular bodies, one end of each of which is open and the other end is closed by the bottom, and from a connection section for connecting the tubular bodies, and having piezoelectric elements individually provided on the inner bottom surfaces of the tubular bodies, reverberation caused by vibration of one of the piezoelectric element may affect the other piezoelectric element through the connection section. Tubular bodies ( 11, 12 ) having the bottoms are connected through a connection section ( 13 ) to portions of side surface sections ( 11   b   , 12   b ) near bottom sections ( 11   c   , 12   c ), the portions being portions at which displacement by vibration of piezoelectric elements ( 51   a   , 51   b ) is minimum.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an ultrasonic sensor that is used, for example, as a back-up sensor for automobiles. 
         [0003]    2. Description of the Related Art 
         [0004]    An ultrasonic sensor is a sensor that uses ultrasonic waves to perform sensing. The ultrasonic sensor includes a piezoelectric transducer, which intermittently sends ultrasonic waves (transmission waves) and receives reflected waves (reception waves) from an object. The distance between the ultrasonic sensor and the object is measured via the transmission/reception wave signals. The piezoelectric transducer is disposed on the inner bottom surface of a bottom portion of a tubular container. The tubular container is mounted in a supporting member such that the outer bottom surface, which serves as a vibrating surface, of the bottom portion is located substantially opposite to the object. 
         [0005]    Known ultrasonic sensors include a single piezoelectric device acting as both a transmitter and a receiver. In this case, as an ultrasonic sensor and an object approach each other, reverberations of one of a transmission signal and a reception signal affect the other signal more strongly and cause a problem in that the object cannot be properly detected. In a configuration proposed to solve this problem, two piezoelectric devices, one that acts as a transmitter and the other that acts as a receiver, are disposed in respective tubular containers. However, while the effects of reverberating vibrations are reduced, this configuration has led to the problems of an increased number of components and increased assembly costs. 
         [0006]    Japanese Unexamined Patent Application Publication No. 10-206529 discloses an ultrasonic transmitting-receiving apparatus in which two piezoelectric devices are disposed in respective tubular containers that are connected together to form an integral housing. This apparatus is configured such that reverberations of both transmission and reception signals are prevented from affecting each other. 
         [0007]      FIG. 10  is a cross-sectional view showing an ultrasonic sensor of the ultrasonic transmitting-receiving apparatus disclosed in Japanese Unexamined Patent Application Publication No. 10-206529. In an ultrasonic sensor  90 , two tubular containers  92   a  and  92   b  and a connecting portion  92   c  that connects the two tubular containers  92   a  and  92   b  form an integral housing  92  having conductivity. An end of the ultrasonic sensor  90  is closed by bottom portions  92   a   1  and  92   b   1  acting as vibrating surfaces, while openings at the other end of the ultrasonic sensor  90  are covered with circuit boards  92   f  and  92   g . The two tubular containers  92   a  and  92   b  are connected to each other, through the connecting portion  92   c , at side portions near the openings of the tubular containers  92   a  and  92   b . Piezoelectric devices  92   d  and  92   e  are disposed on the respective inner bottom surfaces of the bottom portions  92   a   1  and  92   b   1  of the housing  92 . Shielded wires W 1  and W 2  are connected to the circuit boards  92   f  and  92   g , respectively. Live lead wires  92   h   1  and  92   i   1  extending from the circuit boards  92   f  and  92   g , respectively, are connected to the piezoelectric devices  92   d  and  92   e , respectively. Ground lead wires  92   h   2  and  92   i   2  extending from the circuit boards  92   f  and  92   g , respectively, are connected to portions of the bottom portions  92   a   1  and  92   b   1 , respectively, the portions being adjacent to the piezoelectric devices  92   d  and  92   e.    
         [0008]    The housing configuration of the ultrasonic sensor disclosed in Japanese Unexamined Patent Application Publication No. 10-206529 enables the tubular containers to be connected together, through the connecting portion  92   c , at the side portions near the openings where there are fewer vibrations. Therefore, reverberations caused by one of the piezoelectric devices do not substantially affect the other piezoelectric device. A possible reason for which there are fewer vibrations in the side portions near the openings is that the openings, which are covered with the circuit boards  92   f  and  92   g , are subjected to restraining forces of the circuit boards  92   f  and  92   g.    
         [0009]    It is preferable that general ultrasonic sensors have a housing configuration that minimizes interference with vibrations created by piezoelectric transducers. However, as in Japanese Unexamined Patent Application Publication No. 10-206529, covering the openings of the tubular containers with the circuit boards causes interference with such vibrations. If an ultrasonic sensor has a configuration in which openings are not covered, side portions of tubular containers vibrate most strongly at portions near the openings, in response to the vibrations of piezoelectric transducers. Therefore, if tubular containers are connected to each other at side portions near the openings, it is more likely that reverberations of vibrations created by one piezoelectric device affect the other piezoelectric device. 
       SUMMARY OF THE INVENTION 
       [0010]    To overcome the problems described above, preferred embodiments of the present invention provide an ultrasonic sensor having an integral housing including a plurality of tubular containers that are open at one end and closed by bottom portions at the other end and have side portions extending from the one end to the other end, and at least one connecting portion that connects the plurality of tubular containers, and piezoelectric devices disposed on respective inner bottom surfaces of the respective bottom portions of the plurality of tubular containers. In the housing, the side portions of the plurality of tubular containers are connected to each other, through the connecting portion, at portions adjacent to the bottom portions of the tubular containers, with outer bottom surfaces of the respective bottom portions of the plurality of tubular containers being flush with each other. The housing further includes an elastic member that supports the housing. 
         [0011]    The resonant frequency of the connecting portion preferably differs from the drive frequency of the piezoelectric devices. 
         [0012]    In each of the tubular containers, the thickness of a side portion facing toward another tubular container connected through the connecting portion is preferably greater than the thickness of a side portion that is substantially perpendicular to the side portion facing toward the another tubular container. 
         [0013]    The outline of the outer bottom surface of each of the tubular containers is preferably polygonal. 
         [0014]    The outer bottom surfaces of the plurality of tubular containers and an outer surface of the connecting portion preferably form a single flat surface. 
         [0015]    With the ultrasonic sensor of various preferred embodiments of the present invention, since the plurality of tubular containers are connected to each other at side portions that are adjacent to the bottom portions at which the amount of displacement caused by the vibrations of the piezoelectric transducers is smallest, the reverberations of vibrations created by a piezoelectric transducer cannot easily affect another piezoelectric transducer through the connecting portion. This enables accurate detection of an object even if it is located at a close distance from the ultrasonic sensor. 
         [0016]    By varying the resonant frequency of the connecting portion from the drive frequency of the piezoelectric devices, reverberations caused by the vibrations of the piezoelectric transducers are further reduced. 
         [0017]    Moreover, in each tubular container, by setting the thickness of a side portion facing toward an adjacent tubular container greater than the thickness of a side portion that is substantially perpendicular to the side portion facing toward the adjacent tubular container, reverberations caused by the vibrations of the piezoelectric transducers are further reduced. It is particularly preferable if the outline of the outer bottom surface of each tubular container is polygonal, for example, rectangular, since a side portion facing toward an adjacent tubular container is in contact with the connecting portion along a straight line and can be formed to have a uniform thickness greater than the thickness of a side portion distant from the connecting portion, and thus, reverberations are reduced. 
         [0018]    Moreover, configuring the outer bottom surfaces of the bottom portions of the plurality of tubular containers and the connecting portion adjacent to the outer bottom surfaces so as to form a single flat surface is preferable in terms of appearance since, for example, if the ultrasonic sensor is mounted in a bumper of a vehicle, an even surface is exposed to the outside. 
         [0019]    Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is an external perspective view of an ultrasonic sensor according to a first preferred embodiment of the present invention. 
           [0021]      FIG. 2  is an external perspective view of the ultrasonic sensor, as viewed from a different direction. 
           [0022]      FIG. 3  is a cross-sectional view of the ultrasonic sensor. 
           [0023]      FIG. 4A  is a schematic cross-sectional view showing a vibrating state of an ultrasonic sensor, and  FIG. 4B  is a graph showing the amount of displacement of the ultrasonic sensor. 
           [0024]      FIG. 5  is a partial perspective view of a vehicle with a rear bumper in which the ultrasonic sensor is mounted. 
           [0025]      FIG. 6  is a partial cross-sectional view of the vehicle. 
           [0026]      FIG. 7  is an external perspective view of an ultrasonic sensor according to a second preferred embodiment of the present invention. 
           [0027]      FIG. 8  is an external perspective view of an ultrasonic sensor according to a third preferred embodiment of the present invention. 
           [0028]      FIG. 9  is a front view of the ultrasonic sensor. 
           [0029]      FIG. 10  is an external perspective view of the known ultrasonic sensor. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     First Preferred Embodiment 
       [0030]      FIG. 1  is an external perspective view of an ultrasonic sensor according to the first preferred embodiment of the present invention.  FIG. 2  is an external perspective view showing the ultrasonic sensor  1  in  FIG. 1  turned upside down.  FIG. 3  is a cross-sectional view taken along line A-A in the ultrasonic sensor  1  shown in  FIG. 2 . In the ultrasonic sensor  1  of the present preferred embodiment, piezoelectric devices  51   a  and  51   b  that create vibrations are disposed inside an aluminum housing  10 . In the housing  10 , two tubular containers  11  and  12  that are open at one end and closed at the other end by bottom portions  11   c  and  12   c  are connected together by a connecting portion  13  at end portions of side portions  11   b  and  12   b  of the tubular containers  11  and  12 , respectively, the end portions being adjacent to the bottom portions  11   c  and  12   c . In other words, the housing  10  is an integral member including the two tubular containers  11  and  12 . The connecting portion  13  is defined by a plate having a uniform thickness. The side portions  11   b  and  12   b  are also of uniform thickness. As shown in  FIG. 1 , outer bottom surfaces  11   d  and  12   d  of the tubular containers  11  and  12  and an adjacent outer surface of the connecting portion  13  are connected to form a single flat surface. The piezoelectric devices  51   a  and  51   b  are disposed on inner bottom surfaces  11   e  and  12   e , respectively, of the respective tubular containers  11  and  12 . Lead wires (not shown) are attached to the respective piezoelectric devices  51   a  and  51   b  and extend outside the ultrasonic sensor  1  through respective openings  11   a  and  12   a.    
         [0031]    The housing configuration of the present preferred embodiment includes side portions of the tubular containers that are connected to each other, by the connecting portion, near the bottom portions of the tubular containers. The reasons that this configuration is used are as follows. 
         [0032]      FIG. 4A  is a schematic cross-sectional view showing a state in which the side portion  11   b  vibrates in response to the drive of the piezoelectric device  51   a  when a voltage is applied to an ultrasonic sensor  2  having a housing configuration including the single tubular container  11 . A power source, lead wires, and other components that are required for voltage application are omitted from  FIG. 4A , which schematically illustrates only the piezoelectric device  51   a  and the housing including the tubular container  11 . 
         [0033]      FIG. 4B  is a graph showing the amount of displacement (i.e., the width of horizontal vibrations) of the side portion  11   b  which vibrates in response to the application of a voltage. The horizontal axis represents the location in the side portion ranging from the bottom portion  11   c  at zero to an opening  11   a . The vertical axis represents the amount of displacement.  FIG. 4A  and  FIG. 4B  show that the amount of displacement increases as the location in the side portion  11   b  approaches the opening  11   a . This is because, in the side portion  11   b , a portion closer to the opening  11   a  is less affected by the restraining force of the bottom portion  11  while a portion closer to the bottom portion  11   c  is more affected by the restraining force of the bottom portion  11   c , and thus, is inhibited from vibrating. Therefore, in the present preferred embodiment of the present invention, the side portions of the plurality of tubular containers are connected to each other, by the connecting portion, at portions near the bottom portions where the amount of displacement of the side portions is small. In the first preferred embodiment, the connecting portion  13  is disposed at a location that enables the outer bottom surfaces  11   d  and  12   d , where the amount of displacement is smallest, and the outer surface of the connecting portion  13  to form a single flat surface. 
         [0034]    The ultrasonic sensor  1  is mounted, for example, in a bumper of a vehicle to be used as a back-up sensor. 
         [0035]      FIG. 5  is a partial perspective view of the vehicle  52  with the rear bumper  53  in which the ultrasonic sensor  1  is mounted. The outer bottom surfaces  11   d  and  12   d  of the ultrasonic sensor  1  are exposed to the outside, with the side portions  11   b  and  12   b  and openings  11   a  and  12   a  embedded in the rear bumper  53 . 
         [0036]      FIG. 6  is a partial cross-sectional view taken along line B-B in the vehicle  52  shown in  FIG. 5  which shows the ultrasonic sensor  1  as viewed from above. The side portions  11   b  and  12   b  are embedded in the bumper  32  while being covered with an elastic member  54  made of rubber or other suitable material. Supporting the housing  10  by the elastic member  23  in this manner enables the tubular containers  11  and  12  to vibrate freely, with virtually no interference, in response to the drive of the piezoelectric devices  51   a  and  51   b , and thus, enables the effects of preferred embodiments of the present invention to be achieved. 
         [0037]    In addition to the functional effects described above, the present invention has the effect of enhancing the appearance of ultrasonic sensors, as the exposed surface of the ultrasonic sensor  1  is a single flat surface. 
       Second Preferred Embodiment 
       [0038]      FIG. 7  is an external perspective view of an ultrasonic sensor according to the second preferred embodiment of the present invention. While the connecting portion  13  of the first preferred embodiment is preferably defined by a plate having uniform thickness, a connecting portion  33  of the present preferred embodiment includes a recessed portion  33   a  having a reduced thickness. In the tubular containers  11  and  12 , the recessed portion  33   a  is provided on the inner surface opposite the outer surface that is flush with the outer bottom surfaces  11   d  and  12   d . The shapes of the other components of the present preferred embodiment are preferably the same as those of the first preferred embodiment. 
         [0039]    Preferred embodiments of the present invention prevent the reverberations of vibrations created by piezoelectric devices disposed in respective tubular containers including an integral housing from affecting each other. Therefore, in the housing configuration described above, two tubular containers are connected to each other at a location at which the amount of displacement caused by vibrations is smallest. In addition, varying the drive frequency of the piezoelectric devices  51   a  and  51   b  from the resonant frequency of the connecting portion  33  is preferable because it prevents the vibrations from being easily transmitted. These frequencies can be varied by modifying the shape of the connecting portion  33 , for example, by forming a recessed portion, as shown in  FIG. 7 , or conversely, a raised portion in the connecting portion  33 . Another possible method is to adjust the thickness or length of the connecting portion. 
       Third Preferred Embodiment 
       [0040]      FIG. 8  is an external perspective view of an ultrasonic sensor according to the third preferred embodiment of the present invention, as viewed from the openings.  FIG. 9  is a front view of an ultrasonic sensor  4 . The ultrasonic sensor  4  of the present preferred embodiment differs from the ultrasonic sensor  1  of the first preferred embodiment in terms of the thickness of side portions of tubular containers. The shapes of the other components are the same as those of the first preferred embodiment. 
         [0041]    The ultrasonic sensor  4  of the present preferred embodiment includes substantially rectangular tubular containers  41  and  42  whose respective side portions do not have uniform thicknesses. In the tubular containers  41  and  42 , the thickness C of a side portion connected to the connecting portion is greater than the thickness D of a side portion that is substantially perpendicular to the side portion connected to the connecting portion. Specifically, the distance from the outer edge of each of outer bottom surfaces  41   d  and  42   d , which are substantially rectangular in outline, to the outer edge of each of inner bottom surfaces  41   e  and  42   e , in other words, the thickness of each side portion adjacent to the connecting portion  13  is greater than the thickness D, regardless of the location of a contact point  14  along a line between a side portion and the connecting portion  13  (i.e., thickness C 1 =C=C 2 &gt;D). Vibrations of the housing caused by the drive of the piezoelectric devices  51   a  and  51   b  are large in thinner portions of the side portions, and small in thicker portions of the side portions. Therefore, a configuration in which the thickness of a side portion adjacent to the connecting portion  13  is greater than the thickness of a side portion distant from the connecting portion  13  further reduces the effects of vibrations. 
         [0042]    Although, in the present preferred embodiment, each opening of the housing defined by the tubular containers is preferably substantially rectangular in shape, the present invention is not limited to this. For example, each opening may be circular in shape. Likewise, the shape of each piezoelectric device, which is preferably substantially circular in the present preferred embodiment, is not limited to this, and may alternatively be rectangular. 
         [0043]    Although it is preferable that the tubular containers are connected to the connecting portion at side portions closest to the bottom portions, the connecting position of the connecting portion may be slightly shifted toward the openings so as to form a gap therebetween. 
         [0044]    Moreover, the number of tubular containers is not limited to two. For example, the present invention is also applicable to a housing configuration in which three tubular containers are connected by two connecting portions. 
         [0045]    Moreover, filling the tubular containers with elastic members causes virtually no interference with the vibrations of the housing, and thus, does not adversely influence the effects of the present invention. 
         [0046]    While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.