Patent Publication Number: US-7583563-B2

Title: Ultrasonic sensor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is based on and incorporates herein by reference Japanese Patent Application No. 2004-128446 filed on Apr. 23, 2004. 
   FIELD OF THE INVENTION 
   The present invention relates to an ultrasonic sensor used, for instance, in a vehicular obstacle detection device that is attached to a bumper of a vehicle for detecting an obstacle rearward of or at corners of the vehicle. 
   BACKGROUND OF THE INVENTION 
   There is proposed, as a conventional technology, an ultrasonic sensor that is attached to a bumper of a vehicle for detecting obstacles around the vehicle. (Refer to Patent Document 1)
         Patent Document 1: JP-H04-35600 A       

   Here, a vibrating planar member (or vibrating face) of this type of the sensor is exposed in its surface outward of the vehicle, so this exposed surface is painted in the same color as the bumper of the vehicle. Further, the ultrasonic sensor is attached to the bumper or regions around the bumper, so thrown stones or gravels often hit the sensor to cause dents on the surface of the vibrating planar member. These dents or damages then bring about corrosion on the surface. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an ultrasonic sensor less subject to damage and corrosion. 
   To achieve the above object, an ultrasonic sensor is provided with the following. An ultrasonic transducer and a casing are included in the sensor. A metal-made housing, a vibrating planar member, and a driving element are included in the ultrasonic transducer. The housing includes an inner space. The vibrating planar member is formed in the housing, wherein an outward surface of the vibrating planar member constitutes an outward surface of the housing and an inward surface of the vibrating planar member faces the inner space. The driving element is attached on an inward surface of the vibrating planar member for vibrating the vibrating planar member. This ultrasonic transducer is assembled within the casing with at least the outward surface of the vibrating planar member exposed from the casing. Here, the ultrasonic transducer is attached to a vehicle via the casing so that the outward surface of the vibrating planar member is exposed outwardly. Further, a resin film is attached using an adhesive member applied on a rear surface of the resin film to cover all the outward surface of the vibrating planner member. 
   Under this structure, the film can help prevent hitting stones from damaging the vibrating planar member, so that the surface of the vibrating planar member is protected from being damaged and corroded. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
       FIGS. 1A to 1D  are views showing a structure of an ultrasonic transducer of an ultrasonic sensor according to an embodiment of the present invention; 
       FIGS. 2A ,  2 B are views showing a state where an ultrasonic sensor is assembled to a bumper of a vehicle; and 
       FIGS. 3A ,  3 B are graphs showing sound reverberations when different-sized films are glued on a vibrating planar member. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An ultrasonic transducer  10  of an ultrasonic sensor  20  according to an embodiment of the present invention will be explained below.  FIG. 1A  shows a front view of the ultrasonic transducer  10 ;  FIG. 1B  shows a side view; and  FIG. 1C  shows a rear view. The transducer  10  is formed of a housing  11  that has an inner space  13  filled with fillers.  FIG. 1D  shows a sectional side view of the transducer  10  without the fillers. 
   The housing  11  is made of aluminum to be electrically conductive. The housing  11  includes a vibrating planar member (or vibrating face)  11   a . An outward surface of the vibrating planar member  11   a  constitutes an outward surface of the housing  11 , while an inward surface of the vibrating planar member  11   a  faces the inner space  13 , as shown in  FIG. 1D . Inside the housing  11  or within the inner space  13 , a piezoelectric element  12  is contained. The piezoelectric element  12  is attached on an inward surface of the vibrating planar member  11   a . On the outward surface or front surface of the vibrating planar member  11   a , a resin-made film  14  (also referred to herein as a “resin film” or a “film” or a “clear film”)is glued so that the film  14  covers all the front surface of the vibrating planar member  11   a.    
   The resin-made film  14  is a clear circular film formed of polyurethane. An adhesive material is applied on the rear surface of the film  14 . All the surface of the housing  11  is painted in a given color (the same color as that of the bumper of the vehicle). Therefore, the front surface of the vibrating planar member  11   a  looks in the same color as the bumper of the vehicle via the clear film  14 . 
   The piezoelectric element  12  is soldered with one terminal of a lead wire  15 , while a portion on an internal wall of the housing  11  is soldered with the other terminal of the lead wire  15 . Alternate signals are thereby applied on both terminal ends of the piezoelectric element  12  via the housing  11 . Applying the alternate signals drives the piezoelectric element  12  to thereby cause the vibrating planar member  11   a  to vibrate. Namely, the piezoelectric element  12  works as a driving element for vibrating. The inner space  13  is filled with the fillers  16  such as silicon after the lead wire  15  is soldered. 
   The ultrasonic sensor  20  including the ultrasonic transducer  10  is assembled in the bumper  30  of the vehicle, as shown in  FIGS. 2A ,  2 B.  FIG. 2A  shows a front view.  FIG. 2B  shows a side view. 
   The ultrasonic sensor  20  consists of the ultrasonic transducer  10 , a processing circuit board  21 , and a resin-made casing  22  within which the ultrasonic transducer  10  and the processing circuit board  21  are assembled. 
   The processing circuit board  21  applies driving voltage generating ultrasonic on the ultrasonic transducer  10  while processing voltage generated from a counter-electromotive force effect from the ultrasonic transducer  10 . Within the casing  22 , a vibration isolating member  23  (silicon rubber) is provided to surround the ultrasonic transducer  10  for preventing vibration transmission to the casing  22 . Further, silicon resin for preventing moisture is filled rearward of the processing circuit board  21 . The processing circuit board  21  connects via a connector  25  to a controller (not shown), which performs obstacle detection for the rear or corners of the vehicle. 
   The casing  22  has a circular opening face  22   a  through which the ultrasonic transducer  10  and the vibration isolating member  23  are inserted (rightward in  FIG. 2B ) and assembled. Thus, the vibrating planar member  11   a  of the ultrasonic transducer  10  is exposed outwardly via the opening face  22   a . The surfaces of the opening face  22   a  of the casing  22  and the vibrating planar member  11   a  of the ultrasonic transducer  10  become approximately flat and outer circumferences of the two surfaces form concentric circles. 
   The lead wire  15  of the ultrasonic transducer  10  is soldered to the processing circuit board  21  to be electrically connected. The processing circuit board  21  includes a variable resistor (not shown) for adjusting sensitivity of the sensor. This variable resistor can be manually adjustable by turning a given volume. The adjustment of the sensor sensitivity is conducted as follows. A pole as an obstacle is positioned in a given distance away from the ultrasonic sensor  20 . The above variable resistor is adjusted while monitoring output signals, from the processing circuit board  21 , deriving from the pole. 
   After being adjusted, the processing circuit board  21  is inserted from the rear of the casing  22 , and the silicon resin  24  for preventing moisture is filled in the rear portion of the casing  22  to thereby complete the assembling of the ultrasonic sensor  20 . 
   As explained above, the resin-made film  14  is glued over the entire outward surface of the vibrating planar member  11   a  of the ultrasonic transducer  10 , so that the film  14  works to protect the ultrasonic transducer  10   a  from hitting stones or the like to help prevent damage of the surface of the vibrating planar member  11   a . Thus, the surface of the vibrating planar member  11   a  can be prevented from being damaged or corroded. 
   The above-described sensitivity adjustment is performed under condition where this film  14  is being glued on the surface of the vibrating planar member  11   a . For instance, when a film obtained from a market is attached to the vibrating planar member  11   a  after the sensitivity adjustment is completed, the sensitivity degrades to thereby decrease a detectable region. However, as in this embodiment, the sensitivity adjustment is performed under condition where the film  14  is already glued on the vibrating planar member  11   a  of the ultrasonic transducer  10 , the above problems can be solved. 
   Next, sound reverberations generated when different-sized films are glued on a vibrating planar member  11   a  will be explained with reference to  FIGS. 3A ,  3 B.  FIG. 3A  shows sound reverberations generated when the size of the film  14  is the same as or a little larger than that of the front surface of the vibrating planar member  11   a , but does not cover or contact a part of the casing  22  that surrounds the vibrating planar member  11   a  and the vibration isolating member  23 .  FIG. 3B  shows sound reverberations generated when the size of the film  14  is larger than that of the front surface of the vibrating planar member  11   a , and covers or contacts a part of the casing  22 . 
   Here, the sound reverberations means a phenomenon that the vibrating planar member  11   a  continues to vibrate without stopping the vibration even after alternate signals applied to both terminal ends of the piezoelectric element  12  is stopped. The sound reverberations being large and continued long may cause mis-detection of the sensor. 
   As shown in  FIG. 3B , even after the alternate signals are stopped, there are found sound reverberations larger and longer than those in  FIG. 3A . 
   In contrast, in  FIG. 3A , after the alternate signals are stopped, there are scarcely found sound reverberations. The cause of this phenomenon is explained as follows. Since the film  14  contacts the casing  22 , the vibration of the vibrating planar member  11   a  is transmitted via the film  14  to the casing  22 ; contrary, the vibration of the casing  22  is transmitted via the film  14  to the vibrating planar member  11   a . Therefore, when the alternate signals are applied, the casing  22  vibrates along with the vibrating planar member  11   a . Thereafter, when the alternate signals stop, the vibrating planar member  11   a  is going to stop the vibration. However, the vibration of the casing that was vibrating while the alternate signals were being applied is transmitted to the vibrating planar member  11   a , so that the vibrating planar member  11   a  continues vibrating without stopping right away. This results in the sound reverberations. 
   In contrast, in the ultrasonic sensor  20  of this embodiment, the size of the film  14  is the same as or a little larger than that of the front surface of the vibrating planar member  11   a , but does not cover or contact a part of the casing  22  that surrounds the vibrating planar member  11   a  and the vibration isolating member  23 . Therefore, there are no problems deriving from sound reverberations as in  FIG. 3B , so that mis-detection can be prevented. More reliable detection can be thereby achieved. Further, the ultrasonic transducer  10  is disposed via the vibration isolating member  23  within the casing  22 , so that the vibration of the ultrasonic transducer  10  is not easily transmitted to the casing  22 . 
   Further, the size of the film  14  can be designed to be a little smaller than that of the front surface of the vibrating planar member  11   a  so that the film  14  does not contact the casing  22 . However, in this size, a part (peripheral portion) of the front surface of the vibrating planar member  11   a  is exposed outwardly, so that this part is vulnerable to damage and corrosion. When this part is damaged and corroded, the corrosion prevails from this part to thereby possibly cause the entire part of the vibrating planar member  11   a  to be corroded. Therefore, gluing the film  14  as covering the entire surface of the vibrating planar member  11   a  is effective in preventing the foregoing problem. 
   Further, in this embodiment, the housing  11  is colored in the given color, and the clear film  14  is attached, so the vibrating planar member  11   a  can be seen in the same color as in the bumper of the vehicle. However, the paint having the same color as that of the bumper can be applied on the front surface or the rear surface of the film  14 . In this case, the paint on the housing  11  can be eliminated. 
   It will be obvious to those skilled in the art that various changes may be made in the above-described embodiments of the present invention. However, the scope of the present invention should be determined by the following claims.