Abstract:
The present invention has as its object to provide a vehicle passenger detection device that is able to prevent erroneous determinations arising from mechanical hysteresis. The present invention provides a vehicle passenger detection device comprising: weight measurement means, provided with a weight sensor disposed between a seat and floor of a vehicle, that measures the load applied to the seat; fluctuation amplitude detection means that detects the amplitude of fluctuation in values measured by the weight measurement means; correction means that applies a negative correction to the value measured by the weight measurement means when the fluctuation amplitude is smaller than a stipulated value; and passenger presence determination means that determines the presence of a passenger upon the seat by comparing the value measured by the weight measurement means against a stipulated threshold value.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a vehicle passenger detection device and particularly to a vehicle passenger detection device that detects the presence of a passenger upon a seat. 
   2. Background 
   Known examples of such a vehicle passenger detection device include, for example, the device taught by Japanese Unexamined Patent Publication No. 2000-258233. With such a vehicle passenger detection device, a strain gage-type weight measurement device  3  is provided between a seat frame  1  (or the lower rail of the seat slide rails) provided in the lower part of the seat and a seat bracket  2  attached to the floor panel. 
   This weight measurement device  3  consists of a base member  4  provided with a pin hole  4   a  and slot  4   b , an arm  7  pivotally supported upon the base member  4  using a base pin  5  serving as the fulcrum (support axle) and a retainer  6 , a flat spring  10  that is attached to one end of the arm  7  with a bracket pin  8  and retainer  9 , a pin bracket  11  as a load transfer member and a strain gage-type load sensor  12 . In  FIG. 1 , F indicates the front of the vehicle while R indicates the rear of the vehicle. 
   With this device, when the load of the passenger upon the seat is transferred via the pin bracket  11 , flat spring  10  and bracket pin  8  to the end of the arm  7 , this arm  7  is pivotally supported by the base pin  5 , so it rocks about the base pin  5 , the motion of the other end of the arm  7  is transferred to the load sensor  12  and the load of the passenger is detected by the load sensor  12 . With this device, in order to prevent excessive rocking of the arm  7 , bushings are disposed between the arm  7  and base member  4 , and moreover, the base pin  5  on the fulcrum side is pivotally supported in the pin hole  4   a  so that backlash does not occur. 
   However, with a weight measurement device such as that shown in  FIG. 1 , mechanical hysteresis occurs. 
   Mechanical hysteresis refers to a situation wherein, when the passenger exits the vehicle, the load on the seat is released and the seat returns to its original position, and at the stage when the load on the weight measurement device reaches a very small load of roughly 2 kg, for example, this very small load balances against the mechanical resistance of the moving parts within the weight measurement device, and thus the weight measurement device does not return to the zero position as its original position. As a result, even though the passenger is no longer present upon the seat, a constant load continues to be input to the load measurement device of the vehicle passenger detection device. 
   The results of detection by the vehicle passenger detection device are used to control airbag deployment, so the vehicle passenger detection device is required in order to determine the presence of a passenger upon the seat and whether the passenger is an adult or child. With a vehicle passenger detection device as described above, a determination is made among the states of no passenger present or an adult or child passenger present based on the load detected by the weight measurement device and predetermined threshold values. 
   Children are light in weight, so the threshold value for distinguishing between the states of no passenger present and a child passenger present is set to a relatively small value. For this reason, in the state in which mechanical hysteresis causes a constant load to be input to the load measurement device of the vehicle passenger detection device, if cargo is placed upon the seat, then the total load of the load due to the mechanical hysteresis and the load due to cargo may exceed the threshold value for distinguishing the state of no passenger present from the state in which a child passenger is present in the load measurement device of the vehicle passenger detection device. As a result, there is a problem in that the vehicle passenger detection device may erroneously determine that a child is sitting on that seat even though no passenger is present. 
   SUMMARY OF THE INVENTION 
   The present invention was accomplished in order to solve this problem and has as its object to provide a vehicle passenger detection device that is able to prevent erroneous determinations arising from mechanical hysteresis. 
   The present invention was achieved based on the discovery that although mechanical hysteresis occurs when a load is applied to a seat and this load is returned to zero, this mechanical hysteresis is eliminated when the seat is subjected to a certain amount of vibration. 
   The present invention thus provides a vehicle passenger detection device wherein the vehicle passenger detection device comprises: weight measurement means, provided with a weight sensor disposed between a seat and floor of a vehicle, that measures the load applied to the seat; fluctuation amplitude detection means that detects the amplitude of fluctuation in values measured by the weight measurement means; correction means that applies a negative correction to the value measured by the weight measurement means when the fluctuation amplitude is smaller than a stipulated value; and passenger presence determination means that determines the presence of a passenger upon the seat by comparing the value measured by the weight measurement means against a stipulated threshold value. 
   With the present invention having such a constitution, when the fluctuation of the value measured by the weight measurement device is determined to be less than a stipulated amplitude, residual hysteresis is assumed to be present, so the conditions for determining the presence of passengers are changed and the determination of the presence of passengers is performed under conditions with the effects of mechanical hysteresis eliminated. Thus, the detection of passengers can be performed accurately even in a range that is easily affected by mechanical hysteresis. 
   In a preferred embodiment of the present invention, the weight measurement means comprises a plurality of weight sensors, and the fluctuation amplitude detection means detects the amplitude of fluctuation in the values measured by the various weight sensors and further comprises correction control means that controls the negative correction when the amplitude of fluctuation of the values measured by at least one of the weight sensors is greater than said stipulated value. 
   Another embodiment of the present invention comprises: adult passenger determination means that compares the measured value against an adult passenger determination threshold value greater than the threshold value and thus determines if the passenger is an adult or child, and display means that, when the passenger presence determination means determines that a passenger is present and the adult passenger determination means determines that the passenger is a child, disables airbag deployment and activates an indicator that indicates that airbag deployment is disabled. 
   Another embodiment of the present invention is a vehicle passenger detection device where the vehicle passenger detection device comprises: weight measurement means, provided with a weight sensor disposed between a seat and floor of a vehicle, that measures the load applied to the seat; fluctuation amplitude detection means that detects the amplitude of fluctuation in values measured by the weight measurement means; and passenger presence determination means that determines the presence of a passenger by comparing the value measured by the weight measurement means against a stipulated threshold value, wherein: if the amplitude of fluctuation is greater than the stipulated value, the passenger presence determination means compares the value measured by the weight measurement means against a first threshold value to determine the presence of a passenger, and if the value measured by the weight measurement means is smaller than a stipulated value, the passenger presence determination means compares the value measured by the weight measurement means against a hysteresis threshold value greater than the first threshold value to determine the presence of a passenger. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective exploded view showing a vehicle passenger detection device according to the background art and a preferred embodiment of the present invention. 
       FIG. 2  is a side view of a seat equipped with the vehicle passenger detection device according to a preferred embodiment of the present invention. 
       FIG. 3  is a block diagram showing the constitution of the vehicle passenger detection device according to a preferred embodiment of the present invention. 
       FIG. 4  is a flowchart showing the content of the passenger detection process performed by the CPU of the vehicle passenger detection device according to Preferred Embodiment 1 of the present invention. 
       FIG. 5  is a flowchart illustrating the airbag control process performed by the CPU of the vehicle passenger detection device according to Preferred Embodiment 1 of the present invention. 
       FIG. 6  is a flowchart illustrating a modification of the airbag control process according to Preferred Embodiment 1 of the present invention. 
       FIG. 7  is a flowchart illustrating the content of the passenger detection process performed by the CPU of the vehicle passenger detection device according to Preferred Embodiment 2 of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be explained with reference to the drawings. 
     FIG. 2  is a schematic side view of a vehicle seat  20  incorporating the weight measurement device and other components of the vehicle passenger detection device according to preferred embodiments of the present invention. 
   This seat  20  consists of a seat cushion  22 , seat back  24  and headrest  26 , being a passenger seat. Below the seat  20  is disposed a seat bracket  30  secured to the floor panel  28  of the vehicle. To this seat bracket  30  are attached a left/right pair of base members  32  (only one of which is shown) extending toward the front and rear of the vehicle. Each of the base members  32  has the same construction as the base member  4  of  FIG. 1 . Each of these base members  32  is attached to seat slide rails  34  extending toward the front and rear of the vehicle. 
   The seat slide rails  34  consist of an upper rail  34 U secured to the bottom of the seat cushion  22  and a lower rail  34 L secured to the base members  32 . The upper rail  34 U and lower rail  34 L are assembled such that they are able to move relative to each other. With this construction, the seat  20  is mounted such that it is able to move forward and backward with respect to the floor panel  28  via the seat slide rails  34  consisting of an upper rail  34 U and lower rail  34 L. 
   As shown in  FIG. 2 , a load sensor  36  is disposed between the lower rail  34 L and base members  32 . This load sensor  36  is the same as load sensor  12  of  FIG. 1 , and together with other constituent members (not shown) constitutes the same weight measurement device as the weight measurement device  3  of  FIG. 1 . Accordingly, this embodiment is constituted such that the load applied to the seat  20  can be measured by means of the weight measurement device including the load sensor  36 . In addition, to one weight measurement device each is attached to the front and back of each of the base members  32 , so a total of four devices are attached to one seat  20 . 
     FIG. 3  is a schematic block diagram showing the constitution of the vehicle passenger detection device according to the present embodiment. In the present embodiment, a CPU  38  constituting the vehicle passenger detection device is constituted such that it is able to perform airbag deployment control in addition to the passenger detection process. 
   The CPU  38  is constituted so as to accept inputs from a G sensor (collision sensor)  40  and a buckle switch  42  that detects whether the seat belt is buckled. In addition, to the CPU  38  is connected ROM  44  for storing a passenger presence determination program and airbag deployment program and RAM  46  for storing the required data. The CPU  38  is further constituted such that it can send output signals to an inflator driver  50  that inflates an airbag  48 , a first indicator  52  that indicates the presence of a passenger and a second indicator  54  that indicates that the passenger is a child so the airbag is in the disabled state. In this embodiment, the first and second indicators are constituted such that they are lamps visible to the passenger. 
   The content of the processes performed by the CPU  38  of the vehicle passenger detection device of the present embodiment will be described with reference to flowcharts. The process given below is executed immediately upon the ignition switch being turned ON. 
     FIG. 4  is a flowchart showing the content of the passenger detection process performed by the CPU  38 . In Step S 1 , input the seat load W detected by the load sensors  36  and the amplitude of fluctuation of the output value of each load sensor. In the present embodiment, the seat load W is taken to be the sum of the values of the seat loads from each of the four load sensors  36 . In addition, the fluctuation amplitude is taken to be the difference between the maximum value and minimum value of the output of each load sensor during a stipulated period of time, e.g., 750 ms. 
   Next, in Step S 2 , input a signal from the buckle switch  42 . Next, in Step S 3 , read from RAM  46  the first threshold value W 1  which is a threshold value for distinguishing between the state in which no passenger is present and the state in which the passenger is a child (the child presence determination threshold value) and, in Step S 4 , read the second threshold value W 2  which is a threshold value for distinguishing whether a passenger is an adult or child (the adult presence determination threshold value). In the present embodiment, W 1  is set to 7 kg and W 2  is set to 35 kg. 
   Next, advance to Step S 5  and determine whether or not the seat load W is greater than the second threshold value W 2 . If the result of Step S 5  is YES, advance to Step S 6  where the passenger is determined to be an adult. 
   If the result of Step S 5  is NO, advance to Step S 7  and determine whether or not the amplitude of fluctuation in the output value of at least one of the load sensors is greater than a stipulated value (e.g., 2 kg). If the output value of at least one of the load sensors  36  fluctuates by more than the stipulated value, then by this fluctuation it may be assumed that the mechanical hysteresis within the weight measurement device has been eliminated. Accordingly, with the passenger detection device according to the present embodiment, the presence of mechanical hysteresis is assumed based on the amplitude of fluctuation in output values from the load sensor  36 . 
   If the result of Step S 7  is NO, or namely the amplitude of fluctuation in the output values from all load sensor  36  is smaller than the stipulated value, residual mechanical hysteresis is assumed to be present, so advance to Step S 8  and apply a negative correction that subtracts from the seat load W a correction value a equivalent to the mechanical hysteresis (e.g., 2 kg). 
   If the result of Step S 7  is YES and the processing of Step S 8  is complete, advance to Step S 9  and determine whether or not the seat load W is greater than the first threshold value W 1  used to determine the presence of a child. 
   If the result of Step S 9  is NO, advance to Step S 10  and determine whether or not the buckle switch is ON. If the result of Step S 10  is YES, the load on the seat is small but the seat belt is buckled, so a child seat is assumed to be installed. Accordingly, the passenger is determined to be a child in Step S 11 . In addition, if the result of Step S 10  is NO, no passenger is determined to be present in Step S 12 . 
   In addition, if the result is YES in Step S 9 , the seat load W is in the range equivalent to the weight of a child, so advance to Step S 11  and the passenger is determined to be a child. 
   Next, the airbag control process performed by the CPU  38  will be described with reference to the flowchart shown in  FIG. 5 . 
   In Step S 20 , read the results of determination according to the process of  FIG. 4  (adult passenger, child passenger, no passenger) and in Step S 21  read the signal from the G sensor  40 . 
   Next, in Step S 22 , determine whether or not no passenger is present upon the seat based on the results read in Step S 20 . If the result of Step S 22  is YES, namely no passenger is present, advance to Step S 23  and turn off first indicator  52  which reports the presence of a passenger. 
   If the result of Step S 22  is NO, namely an adult or child passenger is present, advance to Step S 24  and turn on the first indicator. Next, advance to Step S 25 , determine whether or not the passenger upon the seat  20  is an adult, and if YES, namely the passenger is an adult, perform the process of enabling airbag deployment in Step S 26 , and turn off (OFF) the second indicator  54  in Step S 27 . 
   Furthermore, advance to Step S 28  and determine whether or not the output value G of the G sensor  40  is greater than the airbag deployment threshold value Go. If the result of Step S 28  is YES, then advance to Step S 29  and deploy the airbag  48  via inflator driver  50 . If the result of Step S 28  is NO, then return to Step S 20 . 
   On the other hand, if the result of Step S 25  is NO and the processing of Step S 23  is complete, either no passenger is present or the passenger is a child so advance to Step S 30 , perform the process of disabling airbag deployment and advance to Step S 31 . In Step S 31 , if the passenger is a child, turn on (ON) the second indicator  54  which indicates that airbag deployment is disabled because the passenger is a child and return to Step S 20 . If no passenger is present, do not turn on the second indicator  54  in Step S 31 . 
   With the present embodiment, if the amplitude of fluctuation of the output value of one of the load sensors among the plurality of load sensors is greater than the stipulated value, the negative correction is controlled, so it is possible to control wasteful corrections. 
   In addition, with this constitution, the state of normal operation of the passenger detection device can be confirmed by means of the first indicator  52 . 
   It should be noted that configuration can be adopted wherein the step of reading the signal from the G sensor  40  in Step S 21  is performed immediately before the step of comparing the output value G of the G sensor  40  against the airbag deployment threshold value Go in Step S 28  as shown in the flowchart of  FIG. 6 . 
   A vehicle passenger detection device according to Preferred Embodiment 2 of the present invention will now be described. The basic constitution of this vehicle passenger detection device is the same as that of the vehicle passenger detection device according to Preferred Embodiment 1 above. The differences from Preferred Embodiment 1 lie in the content of the passenger detection process. The passenger detection process of Preferred Embodiment 2 will be described with reference to the flowchart of  FIG. 7  which shows the passenger detection process performed by the CPU of Preferred Embodiment 2. 
   First, in Step S 40 , input the seat load W detected by the load sensors  36  and the amplitude of fluctuation of the output value of each load sensor. In the present embodiment also, the seat load W is taken to be the sum of the values of the seat loads from each of the four load sensors  36 . In addition, the fluctuation amplitude is taken to be the difference between the maximum value and minimum value of the output of each load sensor during a stipulated period of time, e.g., 750 ms. 
   Next, in Step S 41 , input a signal from the buckle switch  42 . Next, in Step S 42 , read from RAM  46  the first threshold value W 1  which is a threshold value for distinguishing between the state in which no passenger is present and the state in which the passenger is a child (the child presence determination threshold value), in Step S 43  read a hysteresis threshold value W h  greater than the first threshold value and in Step S 44  read the second threshold value W 2  which is a threshold value for distinguishing whether a passenger is an adult or child (the adult presence determination threshold value), respectively. In the present embodiment, W 1  is set to 7 kg, W h  is set to 9 kg and W 2  is set to 35 kg. 
   Next, advance to Step S 45  and determine whether or not the seat load W is greater than the second threshold value W 2 . If the result of Step S 45  is YES, advance to Step S 46  where the passenger is determined to be an adult. 
   If the result of Step S 45  is NO, advance to Step S 47  and determine whether or not the amplitude of fluctuation in the output value of at least one of the load sensors is greater than a stipulated value (e.g., 2 kg). If the output value of at least one of the load sensors  36  fluctuates by more than the stipulated value, then by this fluctuation it may be assumed that the mechanical hysteresis within the weight measurement device has been eliminated. Accordingly, with the passenger detection device according to the present embodiment, the presence of mechanical hysteresis is assumed based on the amplitude of fluctuation in output values from the load sensor  36 . 
   If the result of Step S 47  is NO, or namely the amplitude of fluctuation in the output values from all load sensor  36  is smaller than the stipulated value (e.g., 2 kg), residual mechanical hysteresis is assumed to be present, so advance to Step S 48  and determine whether or not the seat load W is greater than the hysteresis threshold value W h  which is greater than the first threshold value W 1  used to determine the presence of a child. If the result of Step S 38  is YES, advance to Step S 49  where the passenger is determined to be a child. 
   If the result of Step S 48  is NO, advance to Step S 50  and determine whether or not the buckle switch is ON. If the result of Step S 50  is YES, the load on the seat is small but the seat belt is buckled, so the state in which a child seat is assumed to be installed. Accordingly, advance to Step S 49  where the passenger is determined to be a child. 
   If the result of Step S 48  is NO, advance to Step S 50  and determine whether or not the buckle switch is ON. If the result of Step S 50  is YES, the load on the seat is small but the seat belt is buckled, so a child seat is assumed to be installed. Accordingly, advance to Step S 49  and determine the passenger to be a child. In addition, if the result of Step S 50  is NO, advance to Step S 51  and determine no passenger to be present. 
   On the other hand, if the result in Step S 47  is YES, advance to Step S 52  and determine whether or not the seat load W is greater than the first threshold value W 1 . If the result in Step S 52  is YES, advance to Step S 49  and determine the passenger to be a child. In addition, if the result in Step S 52  is NO, advance to Step S 50  and determine whether a child is present or no passenger is present based on the buckle switch. 
   With this constitution, a hysteresis threshold value W h  greater than the first threshold value W 1  used to determine the presence of a child is set, so if hysteresis is assumed to be remaining, the seat load W is compared against the hysteresis threshold value W h  to make a determination with the effects of mechanical hysteresis eliminated. 
   The invention is not limited to only the constitution of the preferred embodiments described above. 
   The first and second indicators in these preferred embodiments are constituted so as to notify the passenger of the indicated content by a lamp being turned on or off, but it is also possible to notify the passenger of the indicated content by turning on lamps of different colors.