Abstract:
A seat-occupant restraining apparatus is provided which includes a bag, accommodated in a shoulder belt, for restraining a seat occupant in a seat, and when a vehicle collides, expands the bag with a high-pressure gas produced by an inflator. A relief valve, which opens according to an increase in the internal pressure of the bag, is provided in a gas passage for supplying the high-pressure gas from the inflator to the bag. If the bag is completely expanded by the high-pressure gas from the inflator and the internal pressure of the bag reaches an appropriate value, the relief valve opens and discharges an extra high-pressure gas from the bag, whereby the internal pressure of the bag can be controlled to the appropriate value without causing variations. According to the above-described constriction, it is possible to realize a stable air vent function superior to that of a vent hole, without providing a vent hole in the bag of an air belt assembly.

Description:
This application is a division of prior application Ser. No. 09/210,371 filed on Dec. 14. 1998 now U.S. Pat. No. 6,109,647. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a seat-occupant restraining apparatus which expands a belt for restraining a seat occupant in a seat at the time of a collision of a vehicle, the belt being expanded with a high-pressure gas supplied from an inflator. 
     2. Description of the Related Art 
     An air belt assembly which includes a bag accommodated in a seat belt so that the bag is expanded to gently restrain a seat occupant at the time of a collision of a vehicle is already known, for example, from Japanese Patent Application Laid-Open No. 6-56001. 
     The bag of such an air belt assembly has a vent hole, and after the bag has been expanded, the internal pressure of the bag is adjusted to an appropriate value by discharging an extra high-pressure gas through the vent hole. 
     However, the vent hole, which is a simple opening formed in the bag and which automatically opens in the process of expansion of the folded bag, involves the problem that if the manner of the expansion of the folded bag varies, the timing or extent of opening of the vent hole does not become constant and it becomes difficult to discharge the extra high-pressure gas at an appropriate time. 
     A buckle assembly, to which a tongue device that is provided on a belt is connected, is pivotally supported on a seat base to be swingable forwardly and rearwardly, in order to compensate for a variation in the angle of the belt due to the forward or rearward position of a seat or the shape of the body of the seat occupant, when the seat occupant wears the seat belt assembly. For the same reasons in the air belt assembly as well, the buckle assembly needs to be supported pivotally to be swingable forwardly and rearwardly. 
     FIG. 14 shows the essential portion of a conventional air belt assembly. A buckle assembly  04 , to which a tongue device  03  is connected, provided at one end of each of a shoulder belt  01  and a lap belt  02 , is pivotally supported on a seat base  05  by a pivot pin  06  to be swingable forwardly and rearwardly. At the time of a collision of the vehicle, the high-pressure gas, produced by an inflator  07 , integrally provided on the buckle assembly  04 , is supplied to the shoulder belt  01  through the buckle assembly  04  and the tongue device  03 , thereby expanding the shoulder belt  01  to gently restrain the seat occupant. In such a conventional air belt assembly, since the inflator  07  is integrally provided on the buckle assembly  04 , as the buckle assembly  04  pivots about the pivot pin  06 , the inflator  07  integrally pivots. This leads to the problem that limitations are put on the design because it is necessary to avoid the interference of the inflator  07  with other members. 
     The magnitudes of the shocks due to collisions of vehicles widely range from a small shock, for which a seat occupant can be fully restrained with only a normal seat belt, to a large shock, for which it is necessary to produce the largest possible restraining force. However, in a case where a seat occupant can be fully restrained, for example, merely by operating an air belt assembly without operating an air bag assembly, if both the air bag assembly and the air belt assembly are operated at the same time, the air bag assembly, which originally need not be used, will be wastefully used and the problem of an economic burden to a user will occur. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-described problems, and a first object of the present invention is to realize a stable air vent function superior to that of a vent hole, without providing a vent hole in the bag of an air belt assembly. 
     A second object of the present invention is to allow a swinging motion of a buckle assembly, while avoiding the interference of an inflator with other members in an air belt assembly. 
     A third object of the present invention is to avoid wasteful use of an air bag assembly and an air betassembly, while ensuring necessary and sufficient restraining force, by controlling the operations of the air bag assembly and the air belt assembly according to the magnitude of shock applied to a vehicle. 
     To achieve the above-described first object, according to a first feature of the present invention, a seat-occupant restraining apparatus is provided which comprises a bag accommodated in a belt for restraining a seat occupant in a seat, and when a vehicle collides, expands the bag with a high-pressure gas produced by an inflator, wherein a relief valve, which opens according to an increase in an internal pressure of the bag, is provided in a gas passage for supplying the high-pressure gas from the inflator to the bag. 
     According to the above-described construction, if the inflator ignites at the time of a collision of the vehicle, a produced high-pressure gas is supplied to the bag accommodated in the belt and the belt is expanded so that the seat occupant can be gently restrained. If the bag completes expanding due to the high-pressure gas from the inflator and the internal pressure of the bag reaches the valve-opening pressure of the relief valve, the relief valve opens to discharge an extra high-pressure gas from the bag. Accordingly, not only is it possible to control the internal pressure of the bag to an appropriate value without causing variations, but it is also possible to freely set the gas-discharging direction of the relief valve and discharge the high-pressure gas in a direction away from the body of the seat occupant. 
     To achieve the first object described above, according to a second feature of the present invention, a seat-occupant restraining apparatus is provided which comprises a bag accommodated in a belt for restraining a seat occupant in a seat, and when a vehicle collides, expands the bag with a high-pressure gas produced by an inflator, wherein a solenoid valve, which opens with a time delay after an ignition of the inflator, is provided in a gas passage for supplying the high-pressure gas from the inflator to the bag. 
     According to the above-described construction, if the inflator ignites at the time of a collision of the vehicle, a produced high-pressure gas is supplied to the bag accommodated in the belt and the belt is expanded so that the seat occupant can be gently restrained. If a sufficient amount of time, which is necessary for the bag to complete expanding, passes after the inflator ignites, the solenoid valve opens to discharge an extra high-pressure gas from the bag. Accordingly, not only is it possible to control the internal pressure of the bag to an appropriate value without causing variations, but it is also possible to freely set the gas-discharging direction of a relief valve and discharge the high-pressure gas in a direction away from the body of the seat occupant. 
     To achieve the first object described above, according to a third feature of the present invention, a seat-occupant restraining apparatus is provided which comprises a bag accommodated in a belt for restraining a seat occupant in a seat, and when a vehicle collides, expands the bag with a high-pressure gas produced by an inflator, wherein a relief valve, which opens according to an crease in an internal pressure of the bag, is provided in a gas passage for discharging the high-pressure gas of the bag into the atmosphere. 
     According to the above-described construction, if the inflator ignites at the time of a collision of the vehicle, a produced high-pressure gas is supplied to the bag accommodated in the belt and the bag is expanded so that the seat occupant can be gently restrained. If the bag completes expanding due to the high-pressure gas from the inflator and the internal pressure of the bag reaches the valve-opening pressure of the relief valve, the relief valve opens to discharge an extra high-pressure gas from the bag. Accordingly, not only is it possible to control the internal pressure of the bag to an appropriate value without causing variations, but it is also possible to freely set the gas-discharging direction of the relief valve and discharge the high-pressure gas in a direction away from the body of the seat occupant. 
     To achieve the first object described above, according to a fourth feature of the present invention, a seat-occupant restraining apparatus is provided which comprises a bag accommodated in a belt for restraining a seat occupant in a seat, and when a vehicle collides, expands the bag with a high-pressure gas produced by an inflator, wherein a solenoid valve, which opens with a time delay after an ignition of the inflator, is provided in a gas passage for discharging the high-pressure gas of the bag into the atmosphere. 
     According to the above described construction, if the inflator ignites at the time of a collision of the vehicle, a produced high-pressure gas is supplied to the bag accommodated in the belt and the bag is expanded so that the seat occupant can be gently restrained. If a sufficient amount of time, which is necessary for the bag to complete expanding, passes after the inflator ignites, the solenoid valve opens to discharge an extra high-pressure gas from the bag. Accordingly, not only is it possible to control the internal pressure of the bag to an appropriate value without causing variations, but it is also possible to freely set the gas-discharging direction of a relief valve and discharge the high-pressure gas in a direction away from the body of the seat occupant. 
     To achieve the second object described above, according to a fifth feature of the present invention, a seat-occupant restraining apparatus is provided comprising: a belt in which a bag, which is expandable, is accommodated and which is supported at its one end on a fixed portion; a tongue device which is provided at the other end of the belt; a buckle assembly which is supported on the fixed portion to be swingable forwardly and rearwardly and to which the tongue device is connected; an inflator which is supported on the fixed portion for producing a high-pressure gas; and a flexible pipe which connects the inflator to the buckle assembly, wherein when a vehicle collides, the bag is expanded by supplying the high-pressure gas produced by the inflator to the bag through the flexible pipe, the buckle assembly, and the tongue device. 
     According to the above-described construction, when the seat occupant sits in a seat and connects the tongue device to the buckle assembly, even if the angle of the belt varies according to the forward or rearward position of the seat or the shape of the body of the seat occupant, the buckle assembly swings together with the tongue device and a variation in the angle of the belt can be absorbed. Even if the buckle assembly swings, the inflator, fixed to a fixed portion, does not swing and has no possibility of interfering with another member. In addition, the high-pressure gas can be smoothly supplied from the inflator to the buckle assembly via the flexible pipe. 
     To achieve the third object described above, according to a sixth feature of the present invention, a seat-occupant restraining apparatus is provided comprising: an air bag inflator, which produces a high-pressure gas; an air bag, which is expanded by the high-pressure gas produced by the air bag inflator and expands in front of a seat occupant sitting in a seat; an air belt inflator, which produces a high-pressure gas; an air belt, which is expanded by the high-pressure gas produced by the air belt inflator in the state of restraining the seat occupant in the seat; shock detecting means for detecting a shock of a collision of a vehicle; and control means for controlling an operation of the air bag inflator and an operation of the air belt inflator on the basis of an output of the shock detecting means, wherein if the shock detected by the shock detecting means is less than a first threshold the control means does not operate any one of the air bag inflator and the air belt inflator, wherein if the shock is not less than the first threshold and less than a second threshold greater than the first threshold, the control means does not operate the air bag inflator and operates the air belt inflator, and wherein if the shock is not less than the second threshold, the control means operates both the air bag inflator and the air belt inflator. 
     According to the above-described construction, if the shock of a collision of the vehicle is less than the first threshold and it is not necessary to strongly restrain the seat occupant, neither the air bag nor the air belt is expanded, and the seat occupant is restrained with only the air belt which functions as a mere seat belt. If the shock is not less than the first threshold and less than the second threshold and it is necessary to comparatively strongly restrain the seat occupant, only the air belt is expanded to produce the necessary and sufficient restraining force. If the shock is not less than the second threshold and it is necessary to strongly restrain the seat occupant, the air bag and the air belt are expanded to produce the maximum restraining force. In this manner, by inhibiting expansion of the air bag or the air belt when sufficient restraining force is obtained with other restraining means, it is possible to prevent wasteful operation of the air bag or the air belt to ease the economic burden on a user. 
     In the embodiment, the first threshold corresponds to the shock with which the vehicle collides head-on against a rigid wall at 16 km/h, while the second threshold corresponds to the shock with which the vehicle collides head-on against a rigid wall at 24 km/h. However, the values of these thresholds are a matter of design choice which can be appropriately varied. 
     The above and other objects, features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawing figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     FIGS. 1 to  4  illustrate a first embodiment of the present invention, as follows: 
     FIG. 1 is a side view of a front seat portion of a vehicle; 
     FIG. 2 is a view taken in the direction of an arrow  2  of FIG. 1; 
     FIG. 3 is a perspective view of an air belt assembly; and 
     FIG. 4 is an enlarged cross-sectional view taken along a line  4 — 4  of FIG.  3 . 
     FIG. 5 is a view similar to FIG. 4, but showing a modification of the first embodiment. 
     FIG. 6 is a view similar to FIG. 4, but showing a second embodiment of the present invention. 
     FIG. 7 is a view similar to FIG. 4, but showing a third embodiment of the present invention. 
     FIG. 8 is a view similar to FIG. 4, but showing a fourth embodiment of the present invention. 
     FIGS. 9 to  11  illustrate a fifth embodiment of the present invention, as follows: 
     FIG. 9 is a perspective view of an essential portion of the air belt assembly; 
     FIG. 10 is a cross-sectional view taken along a line  10 — 10  of FIG. 9; and 
     FIG. 11 is a cross-sectional view taken along a line  11 — 11  of FIG.  10 . 
     FIGS. 12 and 13 illustrate a sixth embodiment of the present invention, as follows: 
     FIG. 12 is a side view of a front seat portion of a vehicle; and 
     FIGS. 13A to  13 C are explanatory views of the operation of the sixth embodiment. 
     FIG. 14 is an explanatory view of a conventional air bag assembly. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention will be described below with reference to the accompanying drawing figures. 
     As shown in FIGS. 1 to  3 , an air belt assembly for restraining a seat occupant (in this embodiment, a driver) in a front right seat  1  includes: a shoulder belt retractor  3 , which is provided in a lower portion of a center pillar  2 ; a lap belt retractor  4 , which is provided below the shoulder belt retractor  3 ; a shoulder belt  6 , which is drawn from the shoulder belt retractor  3  to extend via a slip guide  5  provided in an upper portion of the center pillar  2 ; a lap belt  7 , which is drawn from the lap belt retractor  4 ; a tongue device  8 , which is fixed to an end of each of the shoulder belt  6  and the lap belt  7 ; a buckle assembly  9 , which is fixed to a seat base  10  made from a seat frame or a seat rail and to which the tongue device  8  is connected; and an inflator  11 , which is integrally provided on the buckle assembly  9 . 
     The shoulder belt retractor  3  and the lap belt retractor  4 , which are of known types, serve to drawably wind the shoulder belt  6  and the lap belt  7 , respectively. During a normal state in which an acceleration sensor (not shown) is not detecting an acceleration of not less than a predetermined value, the shoulder belt retractor  3  and the lap belt retractor  4  drawably unlock both belts  6  and  7  to allow movement of the body of the seat occupant, and if the acceleration sensor detects an acceleration of not less than the predetermined value at the time of a collision of the vehicle, the shoulder belt retractor  3  and the lap belt retractor  4  nondrawably lock both belts  6  and  7  to restrain the seat occupant. When the acceleration sensor detects an acceleration of not less than the predetermined value, the inflator  11 , of a known type, ignites and produces a high-pressure gas due to the combustion of a propellant. 
     The lap belt  7  is made from a plain weave belt of synthetic fiber. As shown in FIG. 3, the portion of the shoulder belt  6 , which is to be brought into contact with the chest of the seat occupant, includes: a rubber-made bag  12 , which is formed in a tubular shape; and a cover  13 , which covers the outside of the bag  12 . Each of the bag  12  and the cover  13  normally has a flat strip shape, but if the high-pressure gas is supplied from the inflator  11  to the bag  12 , the bag,  12  is expanded into the state shown in each of FIGS. 1 and 2 and gently restrains the seat occupant. When the cover  13 , made of warp knit, is expanded in the radial direction with the expansion of the bag  12 , the cover  13  shrinks in the longitudinal direction by the corresponding amount to produce an initial tension in the shoulder belt  6 . 
     Referring to FIG. 4 as well, the inflator  11  is fixed to a lower portion of a buckle housing  14  which constitutes the body portion of the buckle assembly  9 , and a buckle  15  is fixed to an upper portion of the buckle housing  14 . An anchor member  17 , which is fixed to the buckle housing  14  at its upper end by a bolt  16 , is supported on the seat base  10  to be swingable forwardly and rearwardly by a pivot pin  18 . The inflator  11  and a connection port  19 , which is opened in an upper wall of the buckle housing  14 , communicate with each other by a gas passage  20 , formed in the inside of the buckle housing  14 . 
     The bag  12  and the cover  13  of the shoulder belt  6 , which are fitted on an upper peripheral surface of a tongue housing  21  of the tongue device  8 , as well as the lap belt  7 , which is fitted to overlap the bag  12  and the cover  13 , are fixed to one another by being fastened by a ring-shaped holder  22 . A tongue  23 , whose upper half is embedded in the inside of the tongue housing  21 , is fixed to the tongue housing  21  by a bolt  24  which is inserted through a holder  22 , the lap belt  7 , the cover  13 , and the bag  12 . A connection pipe  25 , which can be inserted into the connection port  19  of the buckle housing  14 , projects from the lower surface of the tongue housing  21 . A gas passage  26 , which allows the connection port  19  to communicate with the inside of the bag  12 , is formed in the tongue housing  21  and the connection pipe  25 . A release button  27 , for separating the tongue  23  from the buckle  15 , is provided on the buckle housing  14 . 
     The bag  12  of the shoulder belt  6  does not have a vent hole through which to discharge an extra high-pressure gas, but instead, a relief valve  28  is integrally provided in an intermediate portion of the gas passage  20  of the buckle housing  14 . The relief valve  28  includes: a gas discharge hole  29 , which allows the gas passage  20  to communicate with atmospheric air; a valve disc  31 , which is pivotally supported by a pin  30 , and which opens or closes the gas discharge hole  29 ; and a spring  32 , which urges the valve disc  31  in the valve-closing direction. 
     The operation of the first embodiment of the present invention having the above-described construction will be described below. 
     As shown in FIG. 4, if the seat occupant connects the tongue  23 , of the tongue device  8 , to the buckle  15  of the buckle assembly  9 , in order to strap on the air belt assembly, the connection pipe  25  of the tongue device  8  is inserted into the connection port  19  of the buckle assembly  9 . 
     If the acceleration sensor detects an acceleration of not less than the predetermined value at the time of a collision of the vehicle, the inflator  11  ignites to produce a high-pressure gas, and the produced high-pressure gas is supplied to the bag  12  of the shoulder belt  6  through the gas passage  20  of the buckle housing  14  and the gas passage  26  of the tongue housing  21 , thereby expanding the bag  12 . As the shoulder belt  6  is expanded in this manner, the area of contact with the chest of the seat occupant increases compared with the shoulder belt  6  which has not yet expanded, so that the seatoccupant can be restrained far more gently. 
     The relief valve  28  is held in a closed state in the process of expansion of the bag  12 , but if the bag  12  completes expanding and its internal pressure exceeds the valve-opening pressure of the relief valve  28 , the valve disc  31  swings against the urging force of the spring  32  and the extra high-pressure gas produced by the inflator  11  is discharged from the gas passage  20  through the relief valve  28 . In addition, since the expanded bag  12  is compressed by the pressure of the seat occupant who moves forwardly because of his/her own inertia, the relief valve  28  opens to discharge the gas from the bag  12 , whereby it is possible to increase a shock absorption effect to a further extent. 
     In this manner, since the gas is discharged by using the relief valve  28  instead of being discharged through a vent hole in the bag  12 , there is no risk that the vent hole is covered to hinder smooth discharge of the gas or the gas is discharged toward the seat occupant. Accordingly, it is possible to expand the bag  12  at a constant internal pressure at any time, and it is also possible to reliably discharge the gas away from the body of the seat occupant. 
     FIG. 5 shows a modification of the first embodiment, and the modification differs from the first embodiment in the structure of the relief valve  28 . 
     Specifically, the relief valve  28  of the modification is detachably secured to the buckle housing  14 , and a valve disc  34 , which is slidably supported in the inside of a valve housing  33 , is brought into abutment with a valve seat  36  provided in the valve housing  33 , by the elastic force of a spring  35 . Accordingly, if the internal pressure of the bag  12 , which is expanded by the high-pressure gas supplied from the inflator  11 , exceeds the predetermined value, the valve disc  34  slides against the elastic force of the spring  35  and the gas passage  20  is allowed to communicate with openings  37 ,  37  . . . formed in the valve housing  33 , thereby discharging the gas. In accordance with this modification, since the relief valve  28  is detachably secured to the buckle housing  14 , production and maintenance are facilitated, as compared with the case in which the relief valve  28  is integrally provided on the buckle housing  14 . 
     FIG. 6 shows a second embodiment of the present invention, in which the relief valve  28  of the above-described modification is replaced with a solenoid valve  38 . The solenoid valve  38  is connected to a controller  40 , which controls the ignition of the inflator  11 , on the basis of the output of an acceleration sensor  39 . If the acceleration sensor  39  detects the shock of a collision of the vehicle, the controller  40  outputs an ignition signal to the inflator  11  and the bag  12  is expanded by the high-pressure gas produced by the inflator  11 . When the controller  40  outputs a valve-opening signal to the solenoid valve  38  slightly later than the ignition signal, a solenoid  41 , of the solenoid valve  38 , drives the valve disc  34  to move it away from the valve seat  36 , thereby allowing the gas passage  20  to communicate with the openings  37 ,  37  . . . and open the solenoid valve  38 . The time at which the solenoid valve  38  opens is set to coincide with the time at which the bag  12  completes expanding, and the extra high-pressure gas produced by the inflator  11  is discharged through the solenoid valve  38 , which has been opened. 
     In accordance with the second embodiment as well, similarly to the above-described first embodiment, not only is it possible to expand the bag  12  at a stable constant internal pressure, but it is also possible to reliably discharge the gas away from the body of the seat occupant. 
     FIG. 7 shows a third embodiment of the present invention, and the relief valve  28 , of the modification of the first embodiment, shown in FIG. 5, is provided at a different position. Specifically, the tongue housing  21  has a connection pipe  25 ′ and a gas passage  26 ′ for discharging the high-pressure gas, at positions symmetrical to the connection pipe  25  and the gas passage  26  for supplying the high-pressure gas, and the buckle housing  14  has a connection port  19 ′ and a gas passage  20 ′ for discharging the high-pressure gas, at positions symmetrical to the connection port  19  and the gas passage  20  for supplying the high-pressure gas. The relief valve  28 , which is identical in structure to that of the above-described modification, is provided at the downstream end of the gas passage  20 ′ of the buckle housing  14 . With the third embodiment as well, it is possible to achieve effects and advantages similar to those of the above-described first embodiment and the modification. 
     FIG. 8 shows a fourth embodiment of the present invention, and the solenoid valve  38 , of the second embodiment, shown in FIG. 6, is provided at a different position. Specifically, similarly to the third embodiment shown in FIG. 7, the tongue housing  21  has the connection pipe  25 ′ and the gas passage  26 ′ for discharging the high-pressure gas, and the buckle housing  14  has the connection port  19 ′ and the gas passage  20 ′ for discharging the high-pressure gas. The solenoid valve  38 , which is identical in structure to that of the second embodiment shown in FIG. 6, is provided at the downstream end of the gas passage  20 ′ of the buckle housing  14 . With the fourth embodiment as well, it is possible to achieve effects and advantages similar to those of the above-described second embodiment. 
     In any of the above-described first to fourth embodiments, a belt to be expanded is not limited to the shoulder belt  6 , and the lap belt  7  may also be expanded. Although, in each of the first embodiment and the modification thereof as well as the third embodiment, the relief valve  28  is provided on the buckle assembly  9 , the relief valve  28  may also be provided on the tongue device  8 . 
     A fifth embodiment of the present invention will be described below with reference to FIGS. 9 to  11 . 
     The feature of the fifth embodiment resides in the connection between the buckle assembly  9  and the inflator  11 , and the shoulder belt  6 , the lap belt  7 , the tongue device  8  and the buckle assembly  9  are substantially identical in structure to those of each of the first to fourth embodiments. 
     The inflator  11  is fixed to a side surface of the seat base  10  by two mounting bands  50  and  50 , fitted on the periphery of the inflator  11 , and two bolts  51  and  51 , which are inserted through the respective mounting bands  50  and  50 . The inflator  11  and a gas introducing port  52 , which is formed at the bottom of the buckle housing  14 , are connected by a flexible pipe  53  which can be bent. For example, a bellows pipe made of metal or a pressure hose may be used as the flexible pipe  53 . In the fifth embodiment, if the angle of the shoulder belt  6  and the lap belt  7  varies according to the forward or rearward position of the seat  1  or the shape of the body of the seat occupant, the tongue device  8 , connected to the shoulder belt  6  and the lap belt  7 , swings about the pivot pin  18  together with the buckle assembly  9  in a direction A or B as viewed in each of FIGS. 9 and 10, thereby compensating for the variation in such angle. 
     If the acceleration sensor detects an acceleration of not less than a predetermined value at the time of a collision of the vehicle, the inflator  11  ignites and produces a high-pressure gas in response to an ignition command from an ignition controller, and the high-pressure gas is supplied to the bag  12  of the shoulder belt  6  through the flexible pipe  53 , the gas introducing port  52 , the gas passage  20 , and the connection port  19  of the buckle housing  14  and the connection pipe  25 , and the gas passage  26  of the tongue housing  21 . Accordingly, as the shoulder belt  6  is expanded, the area of contact with the chest of the seat occupant increases compared with the shoulder belt  6  which does not yet expand, so that the seat occupant can be restrained far more gently. 
     As described above, since the inflator  11  connected to the buckle assembly  9  via the flexible pipe  53  is non-swingably fixed to the seat base  10 , even if the buckle assembly  9  swings, the inflator  11  has no risk of interfering with another member. Accordingly, the degree of freedom of design can be increased. 
     In the description of the fifth embodiment, the center pillar  2  is illustrated as a fixed portion to which one end of the shoulder belt  6  is connected, and the seat base  10  is illustrated as a fixed portion on which the buckle assembly  9  and the inflator  11  are supported, but such fixed portions are not limited to those of the fifth embodiment. The inflator  11  may be fixed to the inside surface of the seat base  10  as shown by chain double-dashed lines in FIG. 11, instead of being fixed to the outside surface of the seat base  10 . This arrangement makes it possible to achieve effective use of space and an improvement in external appearance at the same time. 
     A sixth embodiment of the present invention will be described below with reference to FIGS. 12 and 13A to  13 C. 
     As shown in FIG. 12, an air bag assembly  63  is provided in the inside of a steering wheel  62  so that a driver sitting in the seat  1  is restrained at the time of a collision of the vehicle. The air bag assembly  63  includes: an air bag inflator  64 , which produces a high-pressure gas at the time of a collision of the vehicle, and an air bag  66 , which is expanded by the high-pressure gas produced by the air bag inflator  64  and breaks a cover  65  of the steering wheel  62  to expand into the chamber of the vehicle. An ignition controller  67  controls the ignition of the air bag inflator  64  on the basis of a signal from an acceleration sensor  68 , which detects an acceleration occurring due to the collision of the vehicle. The ignition controller  67  constitutes control means of the present invention, and the acceleration sensor  68  constitutes shock detecting means of the present invention. 
     An air belt assembly  60 , which restrains the driver in the seat  1 , is substantially identical to the corresponding one of each of the above-described first to fifth embodiments, and the description thereof is omitted. 
     An acceleration which is detected by the acceleration sensor  68  at the time of a collision of the vehicle is inputted to the ignition controller  67 , and the ignition controller  67  calculates the magnitude of the shock of the collision by integrating the acceleration over a preset time, and the magnitude of the shock is compared with a first threshold and a second threshold, both of which are stored in advance. The first threshold corresponds to, for example, the magnitude of a shock which occurs when the vehicle collides head-on against a rigid wall at 16 km/h, while the second threshold corresponds to, for example, the magnitude of a shock which occurs when the vehicle collides head-on against a rigid wall at 24 km/h. 
     If the calculated magnitude of the shock is less than the first threshold, the driver can be fully protected with a normal seat belt and therefore, the ignition controller  67  does not output an ignition signal to either of the air bag inflator  64  and the air belt inflator  11 . Accordingly, as shown in FIG. 13A, the air bag  66  of the air bag assembly  63  is not expanded, and the shoulder belt  6  of the air belt assembly  60  is not expanded, either, whereby the seat occupant is restrained in the seat  1  by the lap belt  7 , of the air belt assembly  60 , and the shoulder belt  6 , which is not expanded. In this manner, if the shock of the collision is small, the ignition of the air bag inflator  64  and that of the air belt inflator  11  are both inhibited, whereby the replacement costs of the air bag assembly  63  and the air belt assembly  60  can be reduced to ease an economic burden on the user. 
     When the calculated magnitude of the shock is not less than the first threshold and less than the second threshold, if the air belt assembly  60  is operated, it is possible to fully restrain the seat occupant without operating the air bag assembly  63 , so that the ignition controller  67  does not output an ignition signal to the air bag inflator  64 , but outputs an ignition signal to only the air belt inflator  11 . Accordingly, as shown in FIG. 13B, the air bag  66  of the air bag assembly  63  is not expanded, and only the shoulder belt  6 , of the air belt assembly  60 , is expanded to gently restrain the seat occupant in the seat  1 . In this manner, if the magnitude of the shock of the collision is not too great, only the air belt assembly  60  is operated and an unnecessary operation of the air bag assembly  63  is avoided, whereby the replacement cost of the air bag assembly  63  can be reduced to ease an economic burden on the user. 
     When the calculated magnitude of the shock is not less than the second threshold, it is necessary to operate both the air bag assembly  63  and the air belt assembly  60  to produce the maximum restraining force, so that the ignition controller  67  outputs ignition signals to both the air bag inflator  64  and the air belt inflator  11 . Accordingly, as shown in FIG. 13C, the air bag  66  of the air bag assembly  63  and the shoulder belt  6  of the air belt assembly  60  are both expanded so that a seat-occupant restraining force can be increased to the maximum by the cooperation between the expanded air bag  66  and the expanded shoulder belt  6 . 
     In this manner, since either or both of the air bag assembly  63  and the air belt assembly  60  are selected and operated according to the magnitude of the shock of collision, it is possible to produce necessary and sufficient restraining force at a minimum cost. 
     Incidentally, although the description of the sixth embodiment has referred to the air bag assembly  63  for a driver&#39;s seat, the present invention can also be applied to an air bag assembly for the seat next to the driver. As a method of detecting the shock of collision, it is possible to adopt an arbitrary method other than the above-described embodiments.