Abstract:
A seatbelt alarm device for a vehicle includes a seat sensor, a seatbelt sensor, a judgment circuit, an alarm unit, and a child seat sensor. The seat sensor detects a mass on a seat of the vehicle. The seatbelt sensor detects whether a seatbelt of the seat is engaged with a seatbelt buckle. The judgment circuit generates a demand for a seatbelt-wear alarm upon determining that a mass sits on the seat and the seatbelt is not engaged according to detection signals of the seat sensor and the seatbelt sensor, respectively. The alarm unit generates the seatbelt-wear alarm. The child seat sensor detects a child seat mounted on the seat. The judgment circuit restricts operation of the alarm unit when the judgment circuit determines that the child seat is mounted to the seat according to a detection signal of the child seat sensor.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based on Japanese Patent Application No. 2004-64649 filed on Mar. 8, 2004, the disclosure of which is incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a seatbelt alarm device for a vehicle and, more particularly, to a seatbelt alarm device that is suitably used for a seat on which a child seat is mounted.  
       BACKGROUND OF THE INVENTION  
       [0003]     Generally, a seatbelt alarm device is mounted in a vehicle for determining whether or not a seatbelt is worn and generating a seatbelt-wear alarm when it is determined that the seatbelt is not worn.  
         [0004]     In one known seatbelt alarm device described in JP-1999-70855A, a seat sensor is provided to detect whether or not a passenger sits on a seat and then generates a corresponding signal. Furthermore, a seatbelt sensor is provided to detect whether or not a seatbelt of the seat is worn and then generates a corresponding signal. When it is determined that a passenger sits on the seat without wearing the seatbelt according to the sitting signal and the seatbelt signal, the seatbelt alarm device generates a seatbelt-wear alarm for inducing the passenger to wear the seatbelt. This seatbelt alarm device can be suitably used for seats in a vehicle.  
         [0005]     For a seat on which a child seat is mounted with the seatbelt, the seat sensor will detect the weight of the child seat and generate a corresponding sitting signal. Furthermore, the seatbelt sensor will detect that the seatbelt is worn and generate a corresponding seatbelt signal. Thus, the above-described seatbelt alarm device determines if the seatbelt of the seat is worn irrespective of whether a child sits in the child seat or not.  
         [0006]     However, in the case where the child seat is mounted on the seat with fasteners or the like as opposed to the seatbelt, the seat sensor will detect the weight of the child seat and generate the sitting signal and the seatbelt sensor will detect that the seatbelt is not being worn. Accordingly, the seatbelt alarm device falsely determines that a passenger sits on the seat without wearing the seatbelt, thereby generating an incorrect seatbelt-wear alarm.  
         [0007]     Therefore, the vehicle may be provided with a switch near a driver so that the driver can manually cancel the seatbelt-wear alarm when the child seat is mounted to the seat. However, this method may require frequent operation of the switch by the driver, which may become impractical or inconvenient.  
       SUMMARY OF THE INVENTION  
       [0008]     In view of the above-described disadvantage, it is an object of the present invention to provide a vehicle seatbelt alarm device that generates a proper seatbelt-wear alarm without the operation of a driver even when a child seat is mounted to the seat.  
         [0009]     According to the present invention, a seatbelt alarm device for a vehicle is provided with a seat sensor, a seatbelt sensor, a judgment circuit, an alarm unit, and a child seat sensor. The seat sensor detects a passenger sitting on a seat of the vehicle based on a load exerted on the seat. The seatbelt sensor detects that a seatbelt of the seat is worn based on a fixing of a wear end of the seatbelt. The judgment circuit generates a demand for generating a seatbelt-wear alarm when the judgment circuit determines that a passenger sits on the seat without wearing the seatbelt according to detection signals of the seat sensor and the seatbelt sensor. The alarm unit generates the seatbelt-wear alarm according to the demand. The child seat sensor detects a child seat that is mounted on the seat without using the seatbelt. The judgment circuit restricts the alarm unit from generating the seatbelt-wear alarm irrespective of whether the seatbelt is worn or not when the judgment circuit determines that the child seat is mounted on the seat according to a detection signal of the child seat sensor.  
         [0010]     That is, even though the seat sensor detects a passenger sitting on the seat when the child seat is fixed on the seat, the judgment circuit can properly determine that the detection is due to the child seat fixed on the seat without using the seatbelt, thus not generating a demand of the seatbelt-wear alarm. Accordingly, a false seatbelt-wear alarm can be restricted even for the seat where the child seat is mounted, without an operation of a driver.  
         [0011]     Preferably, the child seat has a fastening unit, which is inserted into a hole formed on a fastening structure mounted near the seat so that the child seat is detachably fixed to the seat. The child seat sensor is a switch, which is attached to the fastening structure to operate while the fastening unit is inserted into and withdrawn from the hole.  
         [0012]     Accordingly, a mounting of the child seat on the seat can be readily determined according to an action of the fastening unit of the child seat.  
         [0013]     More preferably, the seat sensor is constructed of multiple normally-ON switches connected in parallel. The seatbelt sensor and the child seat sensor are normally-OFF switches. The judgment circuit is a switch circuit constructed of the seat sensor, the seatbelt sensor, the child seat sensor and the alarm unit connected in series. The judgment circuit is supplied with a power source voltage at two ends.  
         [0014]     Accordingly, the judgment circuit can be simply constructed with a low cost to provide proper actuation of a seatbelt-wear alarm.  
         [0015]     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 which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a partial side view of a vehicle interior including a seatbelt alarm device according to a first embodiment of the present invention;  
         [0017]      FIG. 2  is a schematic diagram of a circuit of the seatbelt alarm device according to the first embodiment;  
         [0018]      FIG. 3  is a table of operational conditions for the seatbelt alarm device of the first embodiment of the present invention;  
         [0019]      FIG. 4  is a perspective view of a vehicle seat including a seat sensor of the seatbelt alarm device according to the first embodiment of the present invention;  
         [0020]      FIG. 5  is a plan view of the seat of  FIG. 4 ;  
         [0021]      FIG. 6  is a cross-sectional view of the sitting switch of  FIG. 4  when the seat is vacant;  
         [0022]      FIG. 7  is a cross-sectional view of the sitting switch of  FIG. 4  when the seat is occuppied; and  
         [0023]      FIG. 8  is a schematic diagram of a circuit of a seatbelt alarm device according to a second embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     A first preferred embodiment of the present invention will be described with reference to  FIGS. 1-7 .  
         [0025]     A seatbelt alarm device for a vehicle is provided with a sitting switch  2 , a seatbelt switch  3 , a child seat switch  4 , and a seatbelt alarm lamp  5 , as shown in  FIG. 1 . A child seat  1  is mounted on an upper surface of a sitting portion of a seat  6  without using a seatbelt.  
         [0026]     The sitting switch  2  is constructed of multiple film switches  15 - 18  (shown in  FIG. 2  and described later), which are connected with each other in parallel and laid on a seat cushion that is enfolded by a cover of the seat  6 .  
         [0027]     The seatbelt switch  3  is fixed to a seatbelt buckle  7 , which is mounted at a side surface of the sitting portion of the seat  6 . A fastening unit (not shown) is attached to the seatbelt so that the seatbelt can be fastened when the fastening unit is inserted into a hole formed in the seatbelt buckle  7 . While the fastening unit is inserted into or withdrawn from the hole, that is, while the seatbelt is fastened or unfastened, the seatbelt switch  3  will intermittently operate.  
         [0028]     The child seat switch  4  is fixed to a child-seat buckle  8 , which is accommodated in the seat  6  near a boundary between a back portion and the sitting portion of the seat  6 . The child-seat buckle  8  is provided with a hole, which is disposed at the lower end of the back portion of the seat  6  and extends horizontally rearward. The child seat  1  is provided with a rod  9 , which may also be referred to hereinafter as a fastening unit, protruding from a rear side surface of a sitting portion of the child seat  1 , in which a front-rear direction corresponds to a longitudinal direction of the vehicle. While the rod  9  is inserted into or withdrawn from the hole formed in the child-seat buckle  8 , that is, the child seat  1  is attached to or detached from the seat  6 , the child seat switch  4  will correspondingly intermittently operate.  
         [0029]     Specifically, a lever (not shown) is provided for each of the child-seat buckle  8  and the seatbelt buckle  7  to face the hole thereof. Each lever is biased inward in a radial direction of the hole by a spring (not shown). When the fastening unit of the seatbelt is inserted into the seatbelt buckle  7  or the rod  9  of the child seat  1  is inserted into the hole of the child seat buckle  8 , the respective lever will be displaced radially outward of the hole so that the seatbelt switch  3  or the child seat switch  4  is turned on. On the other hand, when the fastening unit or the rod  9  is withdrawn from the respective hole, the respective lever moves radially inward of the hole to return to its original position due to a returning force of the spring so that the seatbelt switch  3  or the child seat switch  4  is turned off.  
         [0030]     During installation, the child seat  1  is pushed toward the rear side of the vehicle such that the rod  9  aligns with the hole of the child-seat buckle  8 . The rod  9  is inserted into the hole of the child-seat buckle  8 , so that the child seat  1  is fixed to and restrained by the seat  6 .  
         [0031]     Moreover, the seatbelt buckle  7  and the child-seat buckle  8  are separately provided with a depression unit (not shown), which may alternatively be referred to as an unfastening unit. When a user depresses the depression units of the buckles  8  and  7 , the rod  9  and the fastening unit of the seatbelt are unfastened from the buckles  8  and  7 , respectively. Then, the seatbelt and the child seat  1  can be detached from the buckles  7  and  8 , respectively.  
         [0032]     Alternatively, the child-seat buckle  8  and the rod  9  may be attached to the child seat  1  and the seat  6 , respectively. Moreover, the rod  9  and the child-seat buckle  8  may be replaced by any other restraint devices capable of detachably engaging each other.  
         [0033]     The seatbelt alarm lamp  5  is mounted on an instrument panel in front of a driver seat of the vehicle. When it is determined that the seatbelt is not being worn by a passenger, the seatbelt alarm lamp  5  is turned on.  
         [0034]     Next, with reference to  FIG. 2 , a judgment circuit of the seatbelt alarm device will be described.  
         [0035]     The judgment circuit includes the sitting switch  2 , the seatbelt switch  3 , the child seat switch  4 , the seatbelt alarm lamp  5 , and a resistor r connected in series. The sitting switch  2  is constructed of the film switches  15 - 18  that are connected in parallel. The resistor r is provided for restricting a current through the circuit. One end of the switch circuit is supplied with a predetermined voltage by a power supply (not shown) and the other end thereof is grounded.  
         [0036]     The film switches  15 - 18  are normally-ON switches. The child seat switch  4  and the seatbelt switch  3  are normally-OFF switches. Referring to  FIG. 3 , a seatbelt-wear alarm will be generated in the case where each of the sitting switch  2 , the seatbelt switch  3 , and the child seat switch  4  are ON. This will occur when it is determined that there is a mass sitting on the seat  6 , the seatbelt is not worn, and the child seat  1  is not mounted to the child seat buckle  8 . Therefore, when the seatbelt is not worn in the case where the seatbelt ought to be worn, the seatbelt-wear alarm will be generated for urging a passenger to wear the seatbelt.  
         [0037]     A construction of the sitting switch  2  will now be described referring to  FIGS. 4-7 .  
         [0038]     The sitting switch  2  includes the film switches  15 - 18  and is formed by stamping a film to have a tree portion  20  having a branched configuration and a line portion  30  linearly extending from the tree portion  20 . The sitting portion of the seat  6  is provided with the seat cushion enfolded by the cover made of hide or cloth. The tree portion  20  and a part of the line portion  30  are laid on the cushion and enclosed in the cover. The remainder of the line portion  30  passes through a gap in the sitting portion to downwardly extend along the side surface of the seat portion. The remainder of the line portion  30  is attached to a connector C that is fixed to the bottom of the seat  6 .  
         [0039]      FIG. 6  shows a cross section of film switch  15  when the seat  6  is vacant and  FIG. 7  shows that when the seat  6  is occupied. Film switches  16 - 18  have the same construction as film switch  15 .  
         [0040]     The film switch  15  is one branch of the tree portion  20  and is provided with a lower film  80 , an upper film  90 , a spacer film  10 , electrically conductive layers  11  and  12 , and electrically conductive layers  13  and  14 . The spacer film  10  is made of a resin film and sandwiched between the lower film  80  and the upper film  90 . Electrically conductive layers  11  and  12  are formed on the lower film  80  by printing. Electrically conductive layers  13  and  14  are formed under the upper film  90  by printing.  
         [0041]     Electrically conductive layers  11  and  13  are formed of a silver paste. Electrically conductive layers  12  and  14  are formed of a carbon paste. The electrically conductive layers  11  and  12  define a positive power-supply wire and a connecting point  21  at one side of the film switch  15  (film switch  16 ,  17  or  18 ). Electrically conductive layers  11  and  12  are connected with the positive power-supply wire at the connecting point  22 . Electrically conductive layers  13  and  14  define a negative power-supply wire and a connecting point  22  at the other side of the film switches  15  (film switch  16 ,  17  or  18 ). Electrically conductive layer  13  and  14  are is connected with the negative power-supply wire at the connecting point  22 . The positive and negative power-supply wires extend along the line portion  30  to be connected with a terminal of the connector C. When there is a mass sitting on the seat  6 , the connecting point  21  contacts the connecting point  22 , as shown in  FIG. 7 , so that the film switch  15  is turned on. Similarly, the film switches  16 - 18  can also be turned on.  
         [0042]     A second embodiment will now be described with reference to  FIG. 8 . According to this embodiment, a potential of a connecting point between the seatbelt switch  3  and the child seat switch  4  in the switch circuit (referring to  FIG. 2 ) is transmitted to a power window control unit  101  and an airbag control unit  102 . The power window control unit  101  operates to enable and/or disable a power window adjacent to the seat  6 . The airbag control unit  102  operates to enable and/or disable an airbag corresponding to the seat  6 .  
         [0043]     In the case where the child seat  1  is not mounted on the seat  6 , the sitting switch  2  is OFF and the child seat switch  4  is ON. This outputs a low potential to the power window control unit  101  and the airbag control unit  102 . On the other hand, when the child seat  1  is mounted on the seat  6 , the sitting switch  2  is ON and the child seat switch  4  is OFF. This outputs a high potential to the power window control unit  101  and the airbag control unit  102 .  
         [0044]     In the case where a passenger sits on the seat  6 , the sitting switch  2  is ON and the child seat switch  4  is also ON. This outputs a low potential to the power window control unit  101  and the airbag control unit  102 .  
         [0045]     Accordingly, the power window control unit  101  and the airbag control unit  102  can determine whether the child seat  1  is mounted on the seat  6  or not. Thus, when the child seat switch  4  detects the presence of a child seat  1  mounted on the seat  6 , the power window control unit  101  disables or restricts operation of the power window and the airbag control unit  102  disables or changes an operational mode of the airbag.