Patent Abstract:
To provide an occupant detection system including a sensor for detecting an object in a plurality of predetermined regions by irradiating a plurality of light beams with different predetermined inclination angles toward a seat direction, the sensor being mounted to a ceiling of a vehicle and a control unit which, based upon a detection output of the sensor, determines that the seat is vacant if the number of the predetermined regions where the object is detected is below a predetermined number and determines that an occupant is seated in the seat if the number of the predetermined regions where the object is detected is the predetermined number or more.

Full Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an occupant detection system for detecting whether an occupant is present or absent in a vehicle, which is used for a system such as an air bag system for protecting an occupant at the time of a vehicle collision. In particular, the present invention relates to an occupant detection system mounted to a vehicle such as an automobile, which provides information as to whether an occupant is present or absent in a vehicle, the information being utilized for controlling: an air bag system for protecting an occupant at the time of a vehicle collision; an air conditioning system for controlling temperature inside a vehicle; an alarm system for warning an occupant of a critical condition such as his/her dozing; and the like. 
   2. Description of the Related Art 
   An air bag is used for protecting an occupant by immediately expanding between a steering wheel or a dashboard and the occupant at the time of a vehicle collision. However, there is a case where a driver is seated in a position close to the steering wheel because the driver is short or a case where a child stands in front of a front passenger seat. In such cases, a distance between the steering wheel or the dashboard and the occupant is extremely short. Thus, it is known that the expansion of the air bag causes damage to the occupant. 
   Also, in the case where the occupant in the front passenger seat is a child at the age of six or below, even when being seated in a normal position, it is presumed that it is safer not to expand the air bag. Therefore, in the United States, legislation enforcing obligatory installation of the occupant detection system in an occupant protection system using an air bag is the current tendency. As the occupant detection system that can be used for the occupant protection system, for example, a system described in Japanese Patent Laid-open No. 08-169289 is known. 
   A conventional occupant detection system is described with reference to the accompanying drawing.  FIG. 4  is a diagram showing the structure of the conventional occupant detection system described in Japanese Patent Laid-open No. 08-169289. 
   In  FIG. 4 , reference numeral  10  denotes a vehicle such as an automobile;  11 , a seat such as a driver seat or a front passenger seat which is provided in the vehicle  10 ;  12 , an occupant seated in the seat  11 ;  13 , a steering wheel;  14 , an air bag provided inside the steering wheel  13  or in the dashboard at the front passenger seat  11 ; and  15 , a distance sensor which is provided on a front ceiling of the vehicle  10  and faces in the direction of the seat  11 . Symbol  16   a  denotes a seat position sensor for detecting a position along the front and rear direction of the seat  11 , and symbol  16   b  denotes a seat position sensor provided in the seat back cushion of the seat  11  for detecting a reclining angle thereof. 
   Next, the operation of the occupant detection system of the conventional system will be described with reference to the drawing. 
   In the case where the seat  11  is vacant, the distance sensor  15  detects the position of the seat  11 , and in the case where the occupant  12  is seated in the seat  11 , the distance sensor  15  detects the position of a front surface of the occupant  12 . When the detected position is too close to the air bag  14 , expansion of the air bag  14  is judged to be more dangerous. Thus, even in the case of a frontal collision of the vehicle  10 , the air bag  14  is restrained from expanding. 
   Also, in the case where the position obtained by the distance sensor  15  is identical to the position obtained from outputs of the seat position sensors  16   a  and  16   b , it is judged that the occupant  12  is absent. In the case where the two positions are different, it is judged that the occupant  12  is present. 
   In the case of the frontal collision of the vehicle  10 , it is necessary that, if the occupant  12  is present, the air bag  14  be expanded to thereby protect the occupant  12 . However, it is uneconomical to expand the air bag  14  even in the case of the absence of the occupant  12 . Therefore, in the case where the above-described judgment results in the absence of the occupant  12 , the air bag  14  is restrained from expanding. As a result, the wasteful repair cost can be saved. 
   In the conventional occupant detection system described above, there is a problem in that in order to judge whether the occupant  12  is present or absent, besides the distance sensor  15  provided to the ceiling, it is necessary to provide the seat position sensors  16   a  and  16   b  in the seat  11  and long wirings for integrating the outputs of the seat position sensors  16   a  and  16   b  installed apart from each other. 
   Further, there is another problem in that the wirings are long, thereby causing inconvenience of mounting the system to the vehicle  10 , which results in poor mounting property. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in order to solve the aforementioned problems and has an object to obtain an occupant detection system which is mounted in one place with an excellent mounting property. 
   An occupant detection system according to the present invention includes: a sensor for detecting an object in a plurality of predetermined regions by irradiating a plurality of light beams with different predetermined inclination angles toward a seat direction, the sensor being mounted to a ceiling of a vehicle; and a control unit which, based upon a detection output of the sensor, determines that the seat is vacant if the number of the predetermined regions where the object is detected is below a predetermined number and determines that an occupant is seated in the seat if the number of the predetermined regions where the object is detected is the predetermined number or more. 
   Accordingly, there is an effect in that only counting the number of the regions makes it possible to detect whether the occupant is present or absent. 
   Further, an occupant detection system according to the present invention includes: a first object detection sensor for detecting an object in a plurality of first object detection regions by irradiating a plurality of infrared beams with different predetermined inclination angles toward a seat direction, the first object detection sensor being mounted to a ceiling of a vehicle; a second object detection sensor for detecting the object in a plurality of second object detection regions whose positional phases are shifted with respect to the plurality of the first object detection regions by irradiating a plurality of infrared beams with different predetermined inclination angles toward the seat direction, the second object detection sensor being mounted to the ceiling of the vehicle; and a control unit which, if detection outputs from the first and second object detection sensors are different, determines that one of the first and second object detection sensors malfunctions. 
   Accordingly, there is an effect in that the malfunction of the occupant detection system is prevented. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
       FIG. 1  is a side view showing a structure of an occupant detection system according to Embodiment 1 of the present invention; 
       FIG. 2  shows a structure of an object detection sensor for the occupant detection system according to Embodiment 1 of the present invention; 
       FIG. 3  is a side view showing a structure of an occupant detection system according to Embodiment 2 of the present invention; and 
       FIG. 4  is a side view showing a structure of a conventional occupant detection system. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiment 1 
   An occupant detection system according to Embodiment 1 of the present invention will be described with reference to the drawings.  FIG. 1  is a side view showing a structure of the occupant detection system according to Embodiment 1 which is mounted at a front passenger seat. Note that the identical symbols in the respective drawings indicate the identical or corresponding parts. 
   In  FIG. 1 , reference numeral  10  denotes a vehicle such as an automobile;  11 , a front passenger seat (a seat) provided in the vehicle  10 ;  14 , an air bag provided in a dashboard at the front passenger seat  11 ; and  40 , a sensor main body of the occupant detection system. 
   The sensor main body  40  is provided on an approximately central ceiling of the vehicle  10  and includes six object detection sensors  20  inside the sensor main body  40 , to thereby detect whether an object is present or absent in each of six object detection regions  42   a  to  42   f  arranged in alignment along a side surface of the vehicle  10 . Note that the sensor main body may be mounted on the ceiling of the vehicle  10  substantially directly above the seat  11 . 
     FIG. 2  is a cross sectional view showing a structure of an object detection sensor for the occupant detection system according to Embodiment 1 of the present invention. 
   In  FIG. 2 , reference numeral  20  denotes an object detection sensor;  21 , an LED for emitting infrared rays (a light emitting element);  22 , a projection lens;  41 , an infrared beam that is projected;  23 , a light receiving element;  24 , a lens;  43 , a field of view of the light receiving element  23 ; and  42 , an object detection region which is a portion where the infrared beam  41  and the field of view  43  of the light receiving element  23  intersect each other. 
   Also, in  FIG. 2 , reference numeral  50  denotes a control unit which is provided in the dashboard and includes a CPU and the like. The control unit  50  is connected to the light emitting elements  21  and the light receiving elements  23  provided in the six object detection sensors  20  and the air bag  14 . 
   Next, an operation of the occupant detection system according to Embodiment 1 will be described with reference to the drawings. 
   In  FIG. 2 , based upon control by the control unit  50 , if the infrared beam  41  irradiated from the LED  21  is hit against an object, a light spot develops on the object. If this light spot exits in the field of view  43  of the light receiving element  23 , it can be detected by the light receiving element  23 . 
   That is, only when the surface of the object exists in the region  42  where the infrared beam  41  and the field of view  43  of the light receiving element  23  intersect each other, the light receiving element  23  detects the light spot. Therefore, the object detection sensor  20  functions as the sensor that detects whether the object is present or absent in the object detection region  42  by utilizing the principle of the optical triangulation. 
   In  FIG. 1 , the six object detection sensors  20  irradiate the infrared beams  41   a  to  41   f  from the vicinity of the central ceiling of the vehicle  10  downward and outward in a diagonal directions avoiding a headrest of the seat  11 , so as to be able to detect whether the object is present or absent in the object detection regions  42   a  to  42   f.    
   The object detection regions  42   a  to  42   f  are arranged in alignment along the seat  11  such that, even in the case where the seat back cushion of the seat  11  exists in any position within a recognition range, the seat back cushion of the seat  11  can be detected in less than three of these object detection regions  42 , and in the case where the occupant is present in the seat, the object can be detected in three or more of these object detection regions  42 . Therefore, the control unit  50  can detect whether the occupant is present or absent with a simple process of counting the number of the regions  42  where the object is detected. 
   For example, based upon outputs form the six object detection sensors  20 , when the number of the object detection regions  42  where the object is detected is three or more, the control unit  50  determines that the occupant is present in the seat and, in the case of a frontal collision of the vehicle  10 , expands the air bag  14  to protect the occupant. 
   Also, for example, based upon outputs form the six object detection sensors  20 , when the number of the object detection regions  42  where the object is detected is less than three, the control unit  50  determines that the seat  11  is vacant and, in the case of the frontal collision of the vehicle  10 , that is, even if an acceleration sensor (not shown) is operated, restrains the air bag  14  from expanding. 
   Note that, in Embodiment 1, the example where the number of the object detection sensors  20  is six (=N) and the threshold number of the object detection regions is three (=a) is shown. However, N and a should be appropriately changed depending on the object to be measured, and if the numbers thereof are increased, the measurement range or reliability improves in general. 
   Also, in Embodiment 1, six independent object detection sensors  20  each provided with the light emitting element  21  and the light receiving element  23  are used. However, the total number of the elements may be decreased by dividing light irradiated from one light emitting element into a plurality of light beams through a mirror, a beam splitter, or the like to irradiate the beams in a plurality of directions, or by providing one light receiving element with plural ranges of field of view. 
   Further, in Embodiment 1, the object detection regions  42  are formed by utilizing the principle of the optical triangulation. However, a distance sensor may be provided which is for measuring the distance to the object within the angular range of a given solid angle and below based upon an arbitrary principle, so that the region which is located within the measurement angular range and where the output of the distance sensor is allowed within a given range, may be the object detection region. That is, in the case where the distance detected by the distance sensor is a distance to the object detection region  42 , similarly to the object detection sensor  20 , it can be considered that the object is detected in the object detection region  42 . 
   As described above, according to Embodiment 1, there is an effect in that the occupant detection system can be obtained which is excellent in mounting property and can detect whether the occupant is present or absent even without separately providing the seat position sensor. 
   Embodiment 2 
   An occupant detection system according to Embodiment 2 of the present invention will be described with reference to the drawings.  FIG. 3  is a side view showing a structure of the occupant detection system mounted at a front passenger seat according to Embodiment 2. 
   In  FIG. 3 , similarly to Embodiment 1, symbols  42   a  to  42   f  denote six object detection regions structuring a first system. Symbols  42   g  to  42   l  denote six object detection regions structuring a second system which are arranged such that positional phases thereof are shifted with respect to those of the first system. Symbol  42   m  denotes a fail judgment object detection region which is provided between the sensor main body  40  and the original object detection regions  42   a  to  42   l.    
   Next, an operation of the occupant detection system according to Embodiment 2 will be described with reference to the drawings. 
   Providing the two systems of the object detection regions  42   a  to  42   f  and  42   g  to  42   l  enables a fail judgment in the case of malfunction caused in one of the systems. That is, in the case where the detection outputs from the object detection sensors  20  of the two systems are the same, the control unit  50  determines that the two systems operate normally to perform the similar operation to Embodiment 1 described above. On the other hand, in the case where the detection outputs from the object detection sensors  20  of the two systems are different, the control unit  50  determines that one of the systems malfunctions and does not perform the operation of Embodiment 1 described above. 
   Also, arranging the two systems of the object detection regions  42   a  to  42   f  and  42   g  to  42   l  such that the positional phases thereof are shifted, eliminates a clearance between each of the object detection regions and can improve precision in detection. 
   As described above, according to Embodiment 2, there is an effect in that the occupant detection system can be obtained which is excellent in mounting property and can detect whether the occupant is present or absent even without separately providing the seat position sensor. 
   Embodiment 3 
   In Embodiment 1 and Embodiment 2 described above, in the case where an arm or the like of the occupant in a rear seat of the vehicle  10  is extended between the sensor main body  40  and the original object detection region  42 , the sensor is blocked, which makes it impossible to detect the object in the original detection region  42 . Thus, as shown in  FIG. 3 , the fail judgment object detection region  42   m  is arranged between the sensor main body  40  and the original object detection regions  42   a  to  42   f  and  42   g  to  42   l , so that a fail is outputted in the above-described case. The same applies to the case of Embodiment 1 shown in FIG.  1 . 
   That is, in the case where the detection outputted from the object detection sensors  20  having the object detection region  42   m  exists, the control unit  50  determines that there is a fear that the object detection sensors  20  having the object detection regions  42   a  to  42   f  and  42   g  and  42   l  malfunction and does not perform the operation of Embodiment 1 described above.

Technology Classification (CPC): 1