Abstract:
An aspect of the present invention provides a passenger protection device that includes, a brake pedal sensor configured to detect the amount by which a brake pedal of a vehicle is operated, a webbing, one end of the webbing fixed to the vehicle, configured to restrain a passenger seated on a seat of the vehicle, a retractor connected to the other end of the webbing, the rector configured to retract the webbing and inhibit of the webbing extraction, and an ECU electrically coupled to the brake pedal sensor, the ECU configured to detect that the brake pedal operation amount detected by the pedal sensor exceeds a first threshold value, the ECU configured to revise the threshold value based on safety related information of the vehicle to control the inhibition of the webbing extraction of the retractor.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a passenger protection device configured to retract the webbing of a seatbelt using an electric motor. More particularly the present invention relates to a technology for controlling the retraction of the webbing in accordance with the Situation.  
         [0002]     Japanese Laid-Open Patent Publication No. 2001-253317 discloses a passenger restraining device to determine if an emergency situation exists in which there is the possibility that the vehicle in which the passenger restraining device is installed will come abnormally close to a preceding vehicle or an obstacle and, if such an emergency situation exists, to retract the seatbelt using an electric motor. The passenger restraining device uses information regarding the operation of the brakes by the driver while driving (e.g., depression of the brake pedal, brake fluid pressure) in order to determine if such an emergency situation exists.  
         [0003]     Additionally, Japanese Laid-Open Patent Publication No. 2000-190815 discloses a technology provided with a belt control device configured to control the belt tension of a seatbelt in accordance with the driving conditions of the vehicle and belt wearer status detecting means to detect the posture of a passenger wearing a seatbelt, the belt tension control being executed based on information indicating the detected posture of the belt wearer. With that technology, when the belt wearer is the driver of the vehicle, the device controls the seatbelt tension in such a manner that the seatbelt tension increases as a quantity expressing a vehicle driving operation (e.g., brake pedal depression speed, brake pedal depression force, steering operating angle, etc.) increases, said quantity being detected and provided as vehicle state detection information.  
       SUMMARY OF THE INVENTION  
       [0004]     The technologies disclosed in Japanese Laid-Open Patent Publication No. 2001-253317 and Japanese Laid-Open Patent Publication No. 2000-190815 are configured such that the motor retracts the slack in the seatbelt and restrains the passenger in the same manner whenever an emergency brake operation by the driver is detected. Thus, the surrounding circumstances are not taken into consideration.  
         [0005]     Meanwhile, if one attempts to increase the restraining performance by merely speeding up the timing at which an emergency situation is determined to exist, the degree of passenger protection may improve but the device will be lacking from the perspective of driver comfort because it will become an annoyance.  
         [0006]     The present invention was conceived to address these issues and its object is to provide a passenger protection device that takes the driving conditions into consideration and ensures a high restraining performance without debasing the comfort of the passenger.  
         [0007]     An aspect of the present invention provides a passenger protection device that includes, a brake pedal sensor configured to detect the amount by which a brake pedal of a vehicle is operated, a webbing, one end of the webbing fixed to the vehicle, configured to restrain a passenger seated on a seat of the vehicle, a retractor connected to the other end of the webbing, the retractor configured to retract the webbing and inhibit of the webbing extraction, and an ECU electrically coupled to the brake pedal sensor, the ECU configured to detect that the brake pedal operation amount detected by the pedal sensor exceeds a first threshold value, the ECU configured to revise the threshold value based on safety related information of the vehicle to control the inhibition of the webbing extraction of the retractor. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0008]      FIG. 1  is a diagrammatic view for explaining a first embodiment of a passenger protection device in accordance with the present invention.  
         [0009]      FIG. 2  is a block diagram showing a passenger protection device in accordance with the first embodiment of the present invention and peripheral devices thereof.  
         [0010]      FIG. 3  is a flowchart showing the processing by which the brake operation threshold value for retracting the webbing  102  is revised in response to the parking lights ON signal obtained from the headlight switch  111  and the detection signal obtained from the buckle switch  112 .  
         [0011]      FIG. 4  is a flowchart showing the processing by which the brake operation threshold value for retracting the webbing  102  is revised in response to the wipers ON signal obtained from the wiper switch  110 .  
         [0012]      FIG. 5  is a flowchart showing the processing by which the brake operation threshold value for retracting the webbing  102  is revised in response to the headlights ON signal obtained from the headlight switch  111 .  
         [0013]      FIG. 6  is a flowchart showing the processing by which the brake operation threshold value for retracting the webbing  102  is revised in response to the wipers ON signal obtained from the wiper switch  110  and the headlights ON signal obtained from the headlight switch  111 .  
         [0014]      FIG. 7  is a characteristic diagram illustrating the relationship between the depression amount of the brake pedal  106 , the depression speed of the brake pedal  106 , and the threshold value used for retracting webbing  102 .  
         [0015]      FIG. 8  is diagrammatic view for explaining a second embodiment of a passenger protection device in accordance with the present invention.  
         [0016]      FIG. 9  is a block diagram showing a passenger protection device in accordance with the second embodiment of the present invention and peripheral devices thereof.  
         [0017]      FIG. 10  is a flowchart showing a first revision processing for revising the motor operation threshold value in a passenger protection device  100  in accordance the second embodiment.  
         [0018]      FIG. 11  is a flowchart showing a second revision processing for revising the motor operation threshold value in a passenger protection device  100  in accordance the second embodiment.  
         [0019]      FIG. 12  illustrates the first setting method in which the motor operation threshold value is set as a linear function of the pedal switch time, ie., the amount of time from when the driver starts releasing the accelerator pedal  113  until the driver star depressing the brake pedal  106 , or the release speed the accelerator pedal  113 .  
         [0020]      FIG. 13  illustrates the second setting method in which the motor operation threshold value is set as a higher order function of the pedal switch time, ie., the amount of time from when the driver starts releasing the accelerator pedal  113  until the driver starts depressing the brake pedal  106 , or the release speed the accelerator pedal  113 . 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0021]     Various embodiments of the present invention will be described with reference to the accompanying drawings. It is to be noted that same or similar reference numerals are applied to the same or similar parts and elements throughout the drawings, and the description of the same or similar parts and elements will be omitted or simplified.  
       First Embodiment  
       [0022]      FIG. 1  is a diagrammatic view for explaining a first embodiment of a passenger protection device in accordance with the present invention. The passenger protection device  100  is provided with a webbing  102  that serves to restrain a passenger P sitting in a seat S, and a retractor  103  configured to store the webbing  102  using an electric motor  104  configured to provided power to wind up one end of the webbing  102 . The other end of the seatbelt is fastened to the vehicle body through an anchor arranged on the door side of the seat S.  
         [0023]     The or  103  is configured to retract the webbing  102  and inhibits of extraction of the webbing  102  when the brake pedal operation amount detected by the pedal sensor  107  exceeds a threshold value prevents the webbing  102  from being extracted (drawn out) when the vehicle experiences a prescribed deceleration.  
         [0024]     A tongue is attached in a freely movable manner to an intermediate part of the webbing  102  and is configured to engage in a detachable manner with an inner buckle  105  that is fastened to the vehicle body at a transversely-middle portion of the seat S. The webbing  102  is supported in a freely movable manner at a position between the inner buckle  105  and the retractor  103  by a shoulder anchor  101  provided on an upper portion of the center pillar.  
         [0025]     A brake pedal  106  and a brake pedal sensor  107  configured to detect operation of the brake pedal  106  such as the depression amount and depression speed of the brake pedal  106  are provided at the feet of the passenger P. Also, a headlight switch  111  and a windshield wiper switch  110  are provided on the steering column.  
         [0026]      FIG. 2  is a block diagram showing a passenger protection device in accordance with an embodiment of the present invention and peripheral devices thereof. As shown in the figure, the passenger protection device is provided with an ECU (electronic control unit)  108  configured to control the electric motor  104  in the retractor  103  used for driving the webbing  102 . The ECU  108  receives the following signals in this embodiment: a wipers ON signal obtained from the wiper switch  110 , a headlights ON signal and a parking lights ON signal obtained from the headlight switch  111 , a brake signal obtained from a brake pedal sensor  107 , and a detection signal obtained from the buckle switch  112  (which detects if the tongue is inserted into the inner buckle  105 ). Also, a vehicle speed signal is obtained from a vehicle speed detecting device installed on the vehicle.  
         [0027]     The operation of a passenger protection device  100  in accordance with the first embodiment will now be explained with reference to the flowcharts of FIGS.  3  to  6 . The flowchart of  FIG. 3  shows the processing by which the brake operation threshold value for retracting the webbing  102  is revised in response to the parking lights ON signal obtained from the headlight switch  111  and the detection signal obtained from the buckle switch  112 . First, in step S 1 , the ECU  108  detects if the buckle switch  112  is on or off in order to determine if the tongue is set in the inner buckle  105 . The buckle switch is on when the tongue is set therein. If the buckle switch  112  is on, the ECU  108  proceeds to step S 2 , where it determines if emergency braking has been detected. In this embodiment, the ECU  108  returns to step S 2  if emergency braking is not detected, but the invention is not limited to such an arrangement, it is also acceptable for the ECU  108  to return to step S 1  and detect the on/off state of the buckle switch  112 . In step S 3 , the ECU  108  determines if the parking lights are on. If emergency braking is detected and the parking lights are determined to be on (“Yes” in step S 3 ), the ECU  108  sets the brake operation threshold value (emergency braking threshold value) that serves as the condition for retracting the webbing  102  to a threshold value B. If the parking lights are not on (“No” in step S 3 ), the ECU  108  sets the brake operation threshold value (emergency braking threshold value) that serves as the condition for retracting the webbing  102  to a threshold value A.  
         [0028]      FIG. 7  is a characteristic diagram illustrating the relationship between the depression amount of the brake pedal  106 , the depression speed of the brake pedal  106 , and the threshold value used for retracting webbing  102 . When the threshold value B is used, the webbing  102  is retracted at a smaller brake pedal depression amount than when the threshold value A is used.  
         [0029]     In ambient conditions under which the parking lights are turned on, ie., when the outside environment of the vehicle is dimly lighted, there is the possibility that the brakes will be operated late because the surroundings are difficult to discern. By using the threshold value B, the webbing  102  is retracted early and the passenger restraining performance can be improved.  
         [0030]     The flowchart of  FIG. 4  shows the processing by which the brake operation threshold value for retracting the webbing  102  is revised in response to the wipers ON signal obtained from the wiper switch  110 . The steps preceding step S 13  are the same as steps S 1  and S 2  of  FIG. 3  and are omitted from the figure.  
         [0031]     In this embodiment, if the ECU  108  determines that the wipers are on in step S 13 , it sets the brake operation threshold value that serves as the condition for retracting the webbing  102  to a threshold value C. If the ECU  108  determines that the wipers are not on, it sets the brake operation threshold value that serves as the condition for retracting the webbing  102  to a threshold value A.  
         [0032]     Thus, in ambient conditions under which the windshield wipers are turned on, ie., when it is raining or snowing, the brake operation threshold value is revised from the threshold value A to the threshold value C as shown in  FIG. 7  and, as a result, the webbing  102  is retracted at a smaller depression amount of the brake pedal  106 . When it is raining or snowing, there is the possibility that the brakes will be operated late because of poor visibility. By using the threshold value C, the webbing  102  is retracted early and the passenger can be restrained at a more appropriate timing.  
         [0033]     The flowchart of  FIG. 5  shows the processing by which the brake operation threshold value for retracting the webbing  102  is revised in response to the headlights ON signal obtained from the headlight switch  111 . The steps preceding step S 23  are the same as steps S 1  and S 2  of  FIG. 3  and are omitted from the figure.  
         [0034]     In this example, if the ECU  108  detects that the headlights are on in step S 23 , it sets the brake operation threshold value that serves as the condition for reacting the webbing  102  to a threshold value D. If the ECU  108  determines that the headlights are not on, it sets the brake operation threshold value that serves as the condition for retracting the webbing  102  to the threshold value A.  
         [0035]     Thus, in ambient conditions under which the headlights are turned on, ie., when the vehicle is traveling at night or through a tunnel the brake operation threshold value is revised from the threshold value A to the threshold value D as shown in  FIG. 7  and, as a result, the webbing  102  is retracted at a smaller depression amount of the brake pedal  106 . When it is dark, there is the possibility that the brakes will be operated late. By using the threshold value D, the webbing  102  is retracted early and the passenger can be restrained at a more appropriate timing.  
         [0036]     The flowchart of  FIG. 6  shows the processing by which the brake operation threshold value for retracting the webbing  102  is revised in response to the wipers ON signal obtained from the wiper switch  110  and the headlights ON signal obtained from the headlight switch  111 . The steps preceding step S 33  are the same as steps S 1  and S 2  of  FIG. 3  and are omitted from the figure.  
         [0037]     In this example, if the ECU  108  detects the wipers are on in step S 33  and the headlights are on in step S 34 , it sets the brake operation threshold value that serves as the condition for retracting the webbing  102  early to a threshold value E.  
         [0038]     Thus, in ambient conditions under which both the wipers and the headlights are tuned on, e.g., when the vehicle is traveling at night in rainy weather, the brake operation threshold value set to the threshold value E as shown in  FIG. 7  and, as a result, the webbing  102  is retracted at a smaller depression amount of the brake peal  106 . When the surroundings are dark and visibility is poor due to rain, there is the possibility that the brakes will be operated late. By using the threshold value E, the webbing  102  is retracted early and the passenger can be restrained at a more appropriate timing.  
         [0039]     In this way, a passenger protection device  100  in accordance with the present embodiment can revise the brake option threshold value used to the webbing  102  based on safety related information that includes, but not limited to, the on/off status of the parking lights, the windshield wipers, and the headlights. The threshold value can be set to a value well-suited to the quality of the outside visibility and the webbing  102  can be retracted based on the threshold value. Thus, the passenger can be restrained at an even more appropriate timing.  
         [0040]     When the threshold value is revised based on two or conditions from among the on/off status of the parking lights, the on/off status of the windshield wipers, and the on/off status of the headlights, the threshold value is set to a lower value such that the webbing  102  is retracted at an even smaller depression amount of the brake pedal  106 . As a result, the passenger can be restrained at an even more appropriate timing.  
         [0041]     Meanwhile, when the padding lights, the windshield wipers, and the headlights are al off, the brake option threshold value is set to the threshold value A, which is the largest value. As a result, unnecessary retracting of the webbing  102  is avoided and the passenger protection device does not become an annoyance to the passenger. In other words, since the emergency braking threshold value is higher when the visibility is good than when the visibility is poor, the probability of the webbing being retracted for no reason is decreased and the degree of annoyance to the passenger can be reduced.  
         [0042]     Although a passenger protection device in accordance with the present invention has been described heretofore based on an embodiment depicted in the drawings, the present invention is not limited to that embodiment. The constituent features of the various parts can be changed as desired so long as the parts have the same functions.  
         [0043]     For example, although in the previously described embodiment all of the threshold values B, C, and D are different, the present invention is not limited to such a feature and it is also feasible for these threshold values to be the same. Furthermore, although the flowchart of  FIG. 6  presents a case in which the brake operation threshold value is set to a threshold value E that is lower than the threshold values B, C, and D when it is detected that both the wipers and the headlights are on, it is also feasible to set the brake operation threshold value to a value lower than the threshold values B, C, and D when it is detected that both the wipers and the parking lights are on.  
         [0044]     Furthermore, although in the previously described embodiment the wipers ON signal is issued from a wiper switch  110  and the headlights ON and parking lights ON signals are issued from a headlight switch  111 , it is also feasible to detect the actual operation of the wipers and use the resulting detection signal as the wipers ON signal and to detect the illumination of the headlights and parking lights and use the respective resulting detection signals as headlights ON and parking lights ON signals.  
         [0045]     When the vehicle is traveling in rainy weather, in snowy weather, at night, in a tunnel, or in some other condition under which it is more difficult to discern the surroundings of the vehicle than when the vehicle is traveling in clear weather or in the daylight hours, there is the possibility that the driver&#39;s judgment of an emergency situation will be late and thus the timing at which the driver depresses the brake pedal will be late. Thus, there is the possibility the timing at which the electric motor retracts the seatbelt will be late.  
         [0046]     A passenger protection device in accordance with the first embodiment takes the visibility of the vehicles surroundings into consideration and makes it possible to retract the seatbelt at an appropriate timing.  
       Second Embodiment  
       [0047]      FIG. 8  is diagrammatic view for explaining a second embodiment of a passenger protection device in accordance with the present invention. Descriptions of parts that are the same as those of the first embodiment are omitted. A brake pedal  106 , a brake pedal sensor  107  configured to detect the movement of the brake pedal  106 , an accelerator pedal  113 , and an accelerator pedal sensor  109  configured to detect the movement of the accelerator pedal  109  are provided at the feet of the passenger P. The information detected by the brake pedal sensor  107  includes the timing at which the driver starts depressing the brake pedal, the amount by which the brake pedal is depressed, the speed at which the brake pedal is depressed, and other such information related to the movement of the brake pedal  106 . Meanwhile, the information detected by the accelerator pedal sensor  109  includes the amount by which the accelerator pedal is depressed, the timing at which the driver starts releasing the accelerator pedal, the speed at which the accelerator pedal is released, and other such information related to the movement of the accelerator pedal  113 .  
         [0048]     As shown in  FIG. 9 , the passenger protection device  100  of the second embodiment is provided with an ECU  108  configured to control the electric motor  104  used for driving the webbing  102 . The ECU  108  is receives the following signals in this embodiment: a brake signal obtained from the brake pedal sensor  107 , an accelerator signal obtained from the accelerator pedal sensor  109 , and a detection signal obtained from the buckle switch  112  (which detects if the tongue is inserted into the inner buckle  105 ). Also, a vehicle speed signal is obtained from a vehicle speed detecting device (not shown) installed on the vehicle.  
         [0049]     In this embodiment, when a detection value based on a vehicle driving operation (in this embodiment, the depression amount or depression speed of the brake pedal  106 ) exceeds a prescribed motor operation threshold value, the ECU  108  determines that an emergency brake operation has occurred and operates the electric motor  104  so as to retract the webbing  102  and restrain the passenger P.  
         [0050]     Based on detection information from the accelerator pedal sensor  109  and the brake pedal sensor  107 , the ECU  108  revises the motor operation threshold value in accordance with the timing at which the driver starts releasing the accelerator pedal  113  and the timing at which the driver starts depressing the brake pedal  106 . More specifically, the shorter the pedal switch time, i.e., the shorter the difference between the timing at which the driver starts releasing the accelerator pedal  113  and the timing at which the driver stats depressing the brake pedal  106 , the smaller the value to which the motor operation threshold value is revised. Based on the detection information from the accelerator pedal sensor  109 , the faster the release speed of the accelerator pedal  113  is, the smaller the value to which the motor operation threshold value is revised will be. The motor operation threshold value is set as a linear function (first order polynomial) or nonlinear function (higher order polynomial) of the release speed of the accelerator pedal  113  or the pedal switch time, which is the amount of time from when the driver starts releasing the accelerator pedal  113  until the driver starts depressing the brake pedal  106 .  
         [0051]     If the pedal switch time, ie., the amount of time from when the driver starts releasing the accelerator pedal  113  until the driver starts depressing the brake pedal  106 , is short or if the speed at which the accelerator pedal  113  is released is fast, it is highly probable that the depression operation of the brake pedal  8  about to occur will be an emergency brake operation. In such a case, the motor operation threshold value is set to a lower value in order to increase the sensitivity with which emergency braking is detected, thereby enabling an emergency brake operation to be detected with a smaller the depression amount of the brake pedal  106  or a slower depression speed. As a result, the electric motor  104  is operated at an earlier timing and the passenger P is restrained by the reaction of the webbing  102  at an earlier timing.  
         [0052]     The operation of a passenger protection device  100  in accordance with the second embodiment will now be explained with reference to the flowcharts of  FIGS. 10 and 11  and also to diagrams shown in  FIGS. 12 and 13 . The flowchart of  FIG. 10  describes a first revision processing for revising the motor operation threshold value in a passenger protection device  100  in accordance the second embodiment In step S 41  of  FIG. 10 , the ECU  108  determines if the detection signal from the buckle switch  112  is on or off in order to detect if the seatbelt is fastened, ie., if the seatbelt is being worn with the tongue inserted into the inner buckle  105 . If the seatbelt is not fastened, the ECU  108  repeats step S 41 . If the seatbelt is fastened, the ECU  108  proceeds to step S 42 .  
         [0053]     In step S 42 , based on the detection information from the accelerator pedal sensor  109  and the brake pedal sensor  107 , the ECU  108  determines if the accelerator pedal  113  was released and the action of depressing the brake pedal  106  was started in the immediate past. If not, the ECU  108  returns to step S 41 . If so, the ECU  108  reads in the pedal switch time, ie., the difference between the timing at which the driver started releasing the accelerator pedal  113  and the timing at which the driver started depressing the brake pedal  106 , and proceeds to step S 43 .  
         [0054]     In step S 43 , the ECU  108  determines if the acquired pedal switch time is less than a prescribed amount of time. If the pedal switch time is equal to or larger than the prescribed amount of time, the ECU  108  determines that an emergency brake operation has not been detected and returns to step S 41 . If the pedal switch time is less than the prescribed amount of time, the ECU  108  determines that an emergency brake operation has been detected and proceeds to step S 44 .  
         [0055]     In step S 44 , the ECU  108  revises the motor operation threshold value to a smaller value in such a manner that the shorter the pedal switch time (Le., the amount of time from when the driver starts releasing the accelerator pedal  113  until the driver starts depressing the brake pedal  106 ) is, the earlier the timing at which the electric motor  104  is operated becomes.  
         [0056]     The flowchart of  FIG. 11  describes a second revision processing for revising the motor operation threshold value in a passenger protection device  100  in accordance the second embodiment. In step S 51  of  FIG. 11 , the ECU  108  determines if the buckle switch  112  is on or off (based on the detection signal thereof) in order to detect if the seatbelt is fastened, ie., if the seatbelt is being worn with the tongue inserted into the inner buckle  105 . If the seatbelt is not fastened, the ECU  108  repeats step S 51 . If the seatbelt is fastened, the ECU  108  proceeds to step S 52 .  
         [0057]     In step S 52 , based on the detection information from the accelerator pedal sensor  109 , the ECU  108  determines if the accelerator pedal  113  was released in the immediate past. If not, the ECU  108  returns to step S 51 . If so, the ECU  108  reads in the release speed and release amount and proceeds to step S 53 .  
         [0058]     In step S 53 , the ECU  108  determines if the acquired release speed and release amount of the accelerator pedal  113  are equal to or larger than prescribed values. If the release speed and release amount of the accelerator pedal  113  are less than prescribed values, the ECU  108  determines that an emergency brake operation has not been detected and returns to step S 51 . If the release speed and release amount of the accelerator pedal  113  are equal to or larger than prescribed values, the ECU  108  determines that an emergency brake operation has been detected and proceeds to step S 54 .  
         [0059]     In step S 54 , the ECU  108  revises the motor operation threshold value to a smaller value in such a manner that the faster return speed of the accelerator pedal  113  is, the earlier the timing at which the electric motor  104  is operated becomes.  
         [0060]     The method by which the motor operation threshold value is set in step S 44  of  FIG. 10  and step S 54  in  FIG. 11  will now be described in more detail with reference to  FIGS. 12 and 13 .  FIG. 12  illustrates the first setting method in which the motor operation threshold value is set as a linear function of the pedal switch time, ie., the amount of time from when the driver starts releasing the accelerator pedal  113  until the driver starts depressing the brake pedal  106 , or the release speed the accelerator pedal  113 .  
         [0061]     In the upper portion of  FIG. 12 , the motor operation threshold values are shown on a plot in which the vertical axis indicates the depression speed of the brake pedal  106  and the horizontal axis indicates the depression amount of the brake pedal  106 . When the depression speed of the brake pedal  106  is so fast as to exceed the motor operation threshold values A, B, C, and D or when the depression amount of the brake pedal  106  is so large as to exceed the motor operation threshold values A, B, C, and D, the ECR  108  determines that an emergency brake operation has occurred and operates the electric motor  104  so that the webbing  102  is retracted and the passenger P is restrained. In short, the timing at which the webbing  102  of the seatbelt is retracted is advanced by setting the motor operation threshold value to successively lower values A, B, C, and D C (in that order) so that the electric motor  104  is operated when the brake pedal  106  is depressed at comparatively slower depression speeds or the brake pedal  106  is depressed to comparatively smaller depression amounts.  
         [0062]     In the lower portion of  FIG. 12 , the motor operation threshold values are shown on a plot in which the vertical axis indicates the pedal switch time, ie., the amount of time from when the driver starts releasing the accelerator pedal  113  until the driver starts depressing the brake pedal  106 , or the release speed the accelerator pedal  113  and the horizontal axis indicates the depression amount of the brake pedal  106 . Here, the motor operation threshold value is set as a linear function of the vertical axis variable (ie., the pedal switch time or accelerator pedal release speed). In other words, the motor operation threshold value is set in a linear fashion with respect to the pedal switch time or the accelerator pedal release speed in such a manner that the shorter the pedal switch time or the faster the accelerator pedal  113  release speed is, the lower the motor operation threshold value is set. The revision processing executed by the ECU  108  is digital processing and the straight line shown sloping down and to the right in the lower portion of  FIG. 12  would be more accurately depicted as step-like graph. However, it is possible to approach a continuous straight line by revising the motor operation threshold value in finer increments by preparing a larger number of present threshold values (A, B, C, D, E, F, etc.).  
         [0063]      FIG. 13  illustrates the second setting method in which the motor operation threshold value is set as a higher order function of the pedal switch time, ie., the amount of time from when the driver starts releasing the accelerator pedal  113  until the driver starts depressing the brake pedal  106 , or the release speed the accelerator peal  113 .  
         [0064]     The upper portion of  FIG. 13  is the same as the upper portion of  FIG. 12 . In the lower portion of  FIG. 13 , the motor operation threshold values are shown on a plot in which the vertical axis indicates the pedal switch time, ie., the amount of time from when the driver starts releasing the accelerator pedal  113  until the driver starts depressing the brake pedal  106 , or the release speed the accelerator pedal  113  and the horizontal axis indicates the depression amount of the brake pedal  106 . Here, the motor operation threshold value is set as a higher order (curved) function of the vertical axis variable (ie., the pedal switch time or accelerator pedal release speed). In other words, the motor operation threshold value is set in a curved fashion with respect to the pedal switch time or the accelerator pedal release speed in such a manner that the motor operation threshold value becomes gradually smaller when the pedal switch time or accelerator release speed is comparatively slow and becomes smaller more rapidly when the pedal switch time or accelerator release speed is comparatively fast. The revision processing is digital processing executed by the ECU  108  and the straight line shown sloping down and to the right in the lower portion of  FIG. 12  would be more accurately depicted as step-like graph. However, it is possible to approach a continuous straight line by revising the motor operation threshold value A, B, C, and D in finer increments. The revision processing executed by the ECU  108  is digital processing and the curved line shown sloping down and to the right in the lower portion of  FIG. 13  would be more accurately depicted as step-like graph. However, it is possible to approach a continuous curve by revising the motor operation threshold value in finer increments by preparing a larger number of present threshold values (A, B, C, D, E, F, etc.).  
         [0065]     Although  FIG. 12  and  FIG. 13  illustrate cases in which the motor operation threshold value is revised in accordance with the pedal switch time or the accelerator release speed and no explanation is given regarding taking the release amount of the accelerator pedal  113  into consideration, it is certainly possible to revise the motor operation threshold value.  
         [0066]     As explained previously, a passenger protection device in accordance with the second embodiment is a passenger protection device configured to operate an electric motor  104  so as to retract the webbing  102  of a seatbelt and restrain a passenger when a detection value based on safety related information exceeds a motor operation threshold value, said safety related information including such vehicle driving operations as operation of the accelerator pedal and brake pedal. Based on detection information from an accelerator pedal sensor  109  and a brake pedal sensor  107 , an ECU (controller)  108 revises the motor operation threshold value in accordance with the timing at which the driver starts releasing the accelerator pedal  113  and the timing at which the driver starts depressing the brake pedal  106 . By combining information from the accelerator pedal  113  and information from the brake pedal  106 , emergency braking can be detected earlier and more accurately in accordance with the driving conditions and the timing at which the webbing  102  of the seatbelt is retracted can be advanced by revising the motor operation threshold value to a lower value. As a result, the forward movement experienced by the passenger in a collision can be reduced.  
         [0067]     In a passenger protection device in accordance with the second embodiment, the ECU  108  uses detection information from the accelerator pedal sensor  109  and the brake pedal sensor  107  to revise the motor operation threshold value in such a manner that the shorter the pedal switch time, ie., the shorter the difference between the timing at which the driver starts releasing the accelerator pedal  113  and the timing at which the driver starts depressing the brake pedal  106 , the smaller the value to which the motor operation threshold value is revised; or the ECU  108  uses detection information from the accelerator pedal sensor  109  to revise the motor operation threshold value in such a manner that the faster the speed at which the acceleration pedal  113  is released, the smaller the value to which the motor operation threshold value is revised. Thus, unlike technologies that attempt to increase the passenger restraining performance by merely speeding up the timing at which an emergency situation is determined to exist, this embodiment increases the sensitivity with which emergency braking is detected and advances the timing at which the webbing is retracted only when it is highly probable that an emergency brake operation will occur. As a result, a high degree of passenger protection is achieved while also reducing the annoyance associated with emergency braking so that degradation of the passenger&#39;s comfort is avoided.  
         [0068]     Furthermore, in a passenger protection device in accordance with the second embodiment, the motor operation threshold value is set as a linear function or higher order function of the release speed of the accelerator pedal  113  or the pedal switch time, which is the amount of time from when the driver starts releasing the accelerator -pedal  113  until the driver starts depressing the brake pedal  106 . Thus, the function used to revise the motor pedal threshold value can be changed in accordance with the road conditions and driving conditions and emergency braking can be detected earlier and more accurately in accordance with the driving conditions.  
         [0069]     Although in the second embodiment the ECU  108  uses the depression amount and depression speed of the brake pedal  106  as the aforementioned detection values based on vehicle driving operations for determining if the passenger should be restrained by operating the motor  104  and retracting the webbing  102 , the invention is not limited to such an approach. It is also acceptable to use detection information from the accelerator pedal sensor  109 , information regarding the steering angle of the steering wheel  10 , the vehicle speed, a combination of these, or a combination of one or more of these including the detection information from the brake pedal sensor  107 .  
         [0070]     In a passenger protection device in accordance with the second embodiment, detection information from the accelerator pedal sensor and the brake pedal are used to revise the motor operation threshold value in accordance with the timing at which the driver starts releasing the accelerator pedal  113  and the timing at which the driver starts depressing the brake pedal  106 . Thus, by using a combination of information from the accelerator pedal and information from the brake pedal, the second embodiment can detect emergency braking earlier and more accurately in accordance with the driving conditions and the timing at which the webbing of the seatbelt is retracted can be advanced by revising the motor operation threshold value to a lower value. As a result, the forward movement experienced by the passenger in a collision can be reduced. Additionally, unlike technologies that attempt to increase the passenger restraining performance by merely speeding up the timing at which an emergency situation is determined to exist, the second embodiment increases the sensitivity with which emergency braking is detected and advances the timing at which the webbing is retraced only when it is highly probable that an emergency brake operation will occur. As a result a high degree of passenger protection is achieved while also reducing the annoyance associated with emergency braking so that degradation of the passenger&#39;s comfort is avoided.  
         [0071]     The entire contents of Japanese patent applications P2003-369253 filed Oct. 29, 2003, P2003-405941 filed Dec. 4, 2003, are hereby incorporated by reference.  
         [0072]     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all resects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.