Air bag mounting and vent hole arrangement

An airbag of an airbag device has a primary hole for receiving an inflator and a secondary hole for receiving a securing device which secures the inflator to a base plate. A section surrounding the secondary hole is sandwiched between the inflator put in the airbag and the base plate. Therefore, the section of the airbag sandwiched between the inflator and the base plate can be enlarged and thus a high securing strength of the airbag can be acquired. The primary hole can comprise a vent hole that is used to discharge the gas from the inflator to the outside of the airbag. This structure need not make the vent hole separately. Therefore, the airbag is made simple and the production cost thereof becomes lower.

BACKGROUND OF THE INVENTION
 1. Field of the Invention:
 The present invention relates to an airbag device for protecting a
 vehicular occupant by softening a shock of a vehicle collision with an
 airbag inflated when the vehicle collision takes place.
 2. Related Art:
 An airbag device is already known as a vehicular occupant protective device
 to protect a vehicular occupant in case of a vehicle collision. The airbag
 device comprises a sensor for detecting the vehicle collision, an inflator
 for erupting gas based on a signal from the sensor, an airbag that
 inflates with the gas erupted from the inflator, a base plate to which the
 airbag and the inflator are fixed, etc. At the airbag, a hole portion and
 a vent hole are formed. The hole portion is used to insert a gas erupting
 portion of the inflator into the airbag, and the vent hole is used to
 adjust the pressure caused by gas in the airbag.
 FIG. 14 shows an example of an airbag device having such a structure. As
 shown in FIG. 14, a retaining section of an airbag 2 is sandwiched between
 a retainer 13 and a base plate 10 and secured by bolts 15 or rivets. A
 diameter of a hole portion 11 for inserting a gas erupting portion of an
 inflator 9 into the airbag 2 is designed as large as or larger than a
 diameter of the gas erupting portion of the inflator 9. Thus the gas
 erupting portion of the inflator 9 can be inserted into the airbag 2
 through the hole portion 11, and the gas from the inflator 9 can be
 erupted into the airbag 2.
 However, in the airbag device shown in FIG. 14, the retaining section of
 the airbag 2 sandwiched between the retainer 13 and the base plate 10 is
 extremely small. In case of a vehicle collision, high pressure gas from
 the inflator 9 to inflate the air bag 2 acts instantaneously inside the
 airbag 2, and a stress caused by the high pressure gas concentrates on the
 retaining section which is secured to the base plate 10 with the bolts 15.
 Therefore, if the airbag 2 is damaged by the stress, there arises a
 possibility that the retaining section of the airbag 2 slips off the base
 plate 10.
 As another example of prior arts, there is an airbag device disclosed in
 Japanese Unexamined Patent Publication No. 3-292236. An airbag in the
 airbag device has at least one slit for inserting an inflator thereinto.
 The airbag is sandwiched between the inflator and a base plate and secured
 with bolts.
 In the airbag device with the airbag having one slit, there arises a
 possibility that strength of the airbag decline. That is, if the high
 pressure gas acts instantaneously inside the airbag, the slit may tear
 from ends thereof. This causes undesired discharge of the high pressure
 gas to the outside.
 SUMMARY OF THE INVENTION
 It is an object of the present invention to provide an airbag device which
 protects a vehicular occupant certainly by improving strength for securing
 an airbag.
 The object is attained by forming a primary hole for enabling insertion of
 an inflator into an airbag and a secondary hole penetrated by a securing
 device which secures the inflator to a base plate, and sandwiching a
 section surrounding the secondary hole between the inserted inflator and
 the base plate. Thus the section of the airbag sandwiched between the
 inflator and the base plate can be enlarged, so that the high securing
 strength of the airbag can be acquired.
 The primary hole can comprise a vent hole that is used to discharge the gas
 erupted by the inflator to the outside of the airbag. This structure need
 not make a vent hole separately, so that the airbag is made simple and a
 production cost thereof is lower.
 It is desirable to form an cover cloth covering the primary hole of the
 airbag. The cover cloth which covers the whole primary hole prevents the
 gas from discharging to the outside of the airbag. In this case the vent
 hole must be formed independently. Therefore, it is preferable that the
 cover cloth partly covers the primary hole. Due to such a cover cloth, the
 primary hole can discharge a suitable amount of the gas to the outside of
 the airbag in order to adjust pressure in the interior of the airbag. A
 portion of cover cloth can be formed narrow in order to break the cover
 cloth in the case where an abnormal rise of the pressure in the interior
 of the airbag happens.
 It can also sew a patch for strengthening the airbag on the periphery of at
 least one of the primary hole and the secondary hole. This patch and the
 cover cloth can be composed of a single piece of cloth which is sewed to
 the airbag so that producing the airbag become easy.
 It is preferred to form the secondary hole in the shape of a circle. Thus a
 stress caused by a high pressure gas from the inflator acts on a periphery
 of the secondary hole uniformly and the airbag can avoid being damaged.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The present invention will be described in detail with reference to the
 embodiments.
 FIG. 1 is a sectional view illustrating the entire structure of the airbag
 device in the first embodiment. In an airbag device 1, a retaining section
 7 of an airbag 2 is sandwiched between an inflator 9 inserted into the
 airbag 2 and a base plate 10. The inflator 9 is secured to the base plate
 10 by connecting a screw section 16 thereof with a nut 12. The airbag 2 is
 folded and housed in a pad 5. The inflator 9 is connected to a power
 source (not illustrated in the figure) by means of an electrical connector
 51 to receive supply of a starting current. When the starting current is
 supplied to the inflator 9 through the connecter 51, the inflator 9
 generates inflation gas for the airbag 2. An electronic control circuit
 (not illustrated in the figure) controls whether to supply the starting
 current to the inflator 9, based on a signal detected by an acceleration
 sensor (not illustrated in the figure). The acceleration sensor is
 included in the electronic control circuit and outputs the signal when a
 vehicle has crashed. The acceleration sensor need not be located in the
 electronic control circuit. It can also be installed outside the
 electronic control circuit in the vehicle. Furthermore, it is possible to
 eliminate the electronic control circuit and adopt a mechanical
 acceleration sensor which is disposed between the power source and the
 inflator 9. When the acceleration caused by the vehicle collision is
 applied to the mechanical acceleration sensor, a contact of the mechanical
 acceleration sensor is closed and the inflator 9 is connected to the power
 source. It is also possible to install the electronic control circuit or
 the electronic control circuit including the acceleration sensor within
 the base plate 10. The airbag device 1 having such a structure is
 installed in the center of steering wheel 50.
 FIG. 2 and FIG. 3 show a detail of the airbag 2. FIG. 2 is a top plan view
 of the airbag 2 taken on line II--II of FIG.3, which is seen from the
 attachment side of the inflator 9. FIG. 3 is a sectional view of the
 airbag 2 in an inflated state.
 The airbag 2 is formed in the shape of a balloon by sewing a front cloth 2a
 to a rear cloth 2b by means of a thread 3, the front cloth 2a and the rear
 cloth 2b are made of synthetic fiber such as nylon or polyester. The rear
 cloth 2b has a vent hole 4 as the primary hole. The vent hole 4 is used to
 adjust the internal pressure of the airbag 2 in order to absorb the shock
 when the vehicular occupant collides with the airbag 2.
 The inflator 9 is inserted into the airbag 2 through the vent hole 4. Then,
 as described above, the screw section 16 and the connector 51 formed in
 the inflator 9 go through a hole section 11 as the secondary hole. The
 inflator 9 and the airbag 2 are secured to the base plate 10 by connecting
 the screw section 16 and nut 12. The hole section 11 is formed in the size
 that allows the screw section 16 and the connector 51 to pass
 therethrough. The hole section 11 is also formed into a round shape to
 maintain the airbag strength.
 The size of the vent hole 4 is large enough to insert the inflator 9 into
 the airbag 2. However, because the vent hole 4 is used as a passage to
 insert the inflator 9 into the airbag 2 and at the same time it is
 necessary to prevent the inflation gas from discharging too much from the
 vent hole 4, an cover cloth 6 is sewed on the airbag 2 with threads 8 so
 that it partially blocks the vent hole 4. In FIG. 2, the cover cloth 6 is
 sewed on an inner surface of the airbag 2, it is also possible to sew it
 on an outer surface of the airbag 2.
 The operation of the first embodiment explained above will be explained.
 In FIG. 1, the starting current from the power source is supplied to the
 inflator 9 through the connector 51, responding to the acceleration signal
 output from the acceleration sensor when the vehicle has crashed. As a
 result, the inflator 9 generates the inflation gas inside the airbag 2,
 and the internal pressure of the airbag 2 rises due to the inflation gas.
 As the internal pressure rises, the airbag presses on and breaks through
 the pad 6. Following this, the airbag 2 unfolds to be in a shape of a
 balloon and prevents the vehicular occupant from colliding with the
 steering unit 50. At this time, it is possible to absorb the collision
 energy of the vehicular occupant: by releasing appropriately the internal
 gas of the airbag 2 receiving the vehicular occupant. The sizes of the
 vent hole 4 and the cover cloth 6 must be set appropriately because the
 absorption of the collision energy is determined by the relationship
 between the sizes of the vent hole 4 and the cover cloth 6.
 The effects of the first embodiment will be explained. The stress of the
 high pressure gas during an inflation of the airbag 2 and a compression
 stress applied to the airbag 2 when the vehicular occupant collides with
 airbag 2 are concentrated on the retaining section 7 sandwiched between
 the inflator 9 and the base plate 10 or the hole section 11 which is
 formed into the round shape. However, the hole section 11 is formed in an
 extremely small size. This can make the area of the retaining section 7
 larger. As a result, even if the stress described above is applied to the
 retaining section 7, there will be no slipping of the airbag 2. Thus it
 need not secure the airbag 2 by tightening the screw section 16 strongly.
 Furthermore, because bolts or rivets are not used to secure the airbag 2 to
 the base plate 10, the stress described above is distributed uniformly
 over the retaining section 7 and there are no portions where the stress of
 the inflation gas concentrates. Therefore, it is possible to prevent the
 airbag 2 from being damaged by the stress.
 In addition, because the hole section 11 is in the form of a circle, the
 above-mentioned stress is distributed uniformly around the hole section
 11. As a result, there is very little chance that the airbag 2 tears at
 the hole section 11.
 For reasons mentioned above, the airbag 2 has enough strength against the
 stress and it is not necessary to apply a reinforcement cloth around the
 hole section 11 and the vent hole 4. Thus, it is possible to reduce the
 weight of the airbag 2 and also reduce the volume of the folded state.
 For these reasons, the airbag device 1 which includes the airbag 2 can
 definitely protect the vehicular occupant in case of a vehicle collision
 and can be made into a small size and light in weight.
 With reference to FIG. 4 and FIG. 5, the second embodiment will be
 explained. In the explanation hereinafter, only differences in structure,
 operation and effect are described and the same features as those in the
 first embodiment will be omitted for brevity.
 FIG. 4 is a top plan view of the airbag 2 taken on line III--III of FIG. 5,
 which is seen from the attachment side of the inflator 9. FIG. 5 is a
 sectional view of the airbag 2 in an inflated state.
 In the second embodiment, a reinforcement cloth 20 is applied to a
 circumference of the vent hole 4. In such a case, adopting the thinnest
 cloth possible as the reinforcement cloth 20 has the effect of reducing
 the weight of the airbag 2 and reducing the volume of the folded state.
 The cover cloth 6 is sewed on the airbag 2 in a way that it partially
 blocks the vent hole 4 where the reinforcement cloth 20 has been applied.
 Due to the cover cloth 6, the vent hole 4 which discharges the inflation
 gas is set in an appropriate size to adjust the internal pressure of the
 airbag 2 and thus absorbs the shock when the vehicular occupant collides
 with the airbag 2.
 By applying the reinforcement cloth 20 to the area around the vent hole 4,
 it is possible to further reduce the possibility that the airbag 2 breaks
 at the vent hole 4 when the airbag 2 inflates.
 With reference to FIG. 6, the third embodiment according to the present
 invention will be explained. As shown in FIG. 6, a first reinforcement
 cloth 20 for the vent hole 4 and a second reinforcement cloth 21 for the
 hole section 11 are applied to each circumference. The first reinforcement
 cloth 20 and the second reinforcement cloth 21 are connected by the cover
 cloth 6. That is, the cover cloth 6, the first reinforcement cloth 20 and
 the second reinforcement cloth 21 are made of a piece of cloth. The first
 and second reinforcement cloths 20 and 21 achieve reinforcement of the
 area around the vent hole 4 and the hole section 11.
 With such a structure, it is possible to further reduce the possibility
 that the airbag 2 breaks at the hole section 11 and the vent hole 4 when
 the airbag 2 is inflated. In addition, because the cover cloth 6, the
 first reinforcement cloth 20 and the second reinforcement cloth 21 are
 made of a piece of cloth, it is not needed to sew each clothes 6, 20, 21
 separately on the airbag 2, thus reducing the manufacturing cost of the
 airbag device 1.
 With reference to FIG. 7, the fourth embodiment according to the present
 invention will be explained. As shown in FIG. 7, one section of the cover
 cloth 6 is made narrower. As a result, if the vehicle occupant collides
 with the airbag 2 which has inflated upon a vehicle collision, and the
 internal pressure of the airbag 2 rises abnormally high, narrower section
 6a is broken by the internal pressure of the airbag 2. Thus, the internal
 pressure decreases immediately since the inflation gas is discharged
 through the wide area of the vent hole 4.
 In this way, the fourth embodiment includes pressure adjusting mechanism to
 adjust the internal pressure of the airbag 2, and it is possible to
 prevent the airbag 2 from breaking by the high pressure and achieve
 protection of the vehicular occupant.
 With reference to FIG. 8, the fifth embodiment according to the present
 invention will be explained. As shown in FIG. 8, (a) vent holes 4 of an
 appropriate size at two locations, and (b) a slit 17 which functions as
 the primary hole are located separately. It is of course possible to adopt
 a structure with one vent hole 4 or with three vent holes 4. The cover
 cloth 6 is sewed on the airbag 2 so that it covers the slit 17 formed on
 the airbag 2 for insertion of the inflator 9.
 When the cover cloth 6 is lifted up away from the inner surface of the
 airbag 2, the inflator 9 is inserted into the airbag 2 from the slit 17.
 If the airbag 2 inflates in case of the vehicle collision, the internal
 pressure of the airbag 2 is adjusted by the vent holes 4. In such a case,
 the slit 17 is blocked by the cover cloth 6 which is pressed down to the
 inner surface of the airbag 2. Therefore, the inflation gas inside the
 airbag 2 is not discharged to the outside through the slit 17 and thus it
 is possible to avoid any abnormal reduction in the internal pressure of
 the airbag 2.
 As mentioned above, even if the inflator 9 is inserted into airbag 2 from a
 position other than the vent hole 4, it is possible to obtain exactly the
 same effect as in the first embodiment.
 With reference to FIG. 9, the sixth embodiment according to the present
 invention will be explained. As shown in FIG. 9, (a) two vent holes 4 of
 the appropriate size, and (b) an insertion hole 18 which functions as the
 primary hole are located separately. It is of course possible to adopt a
 structure with one vent hole 4 or with three vent holes 4. The insertion
 hole 18 which can insert the inflator 9 into the airbag 2 is blocked by
 the cover cloths 6c and 6d sewed to the airbag 2. In more detail, as shown
 in FIG. 9, two cloths used as the cover cloth are overlapped so that the
 inflator 9 can be inserted from the location where they overlap. With such
 a structure, if the airbag 2 is inflated, the cover cloth 6c is pressed by
 the cover cloth 6d so that the inflation gas inside the airbag 2 is not
 discharged to the outside therefrom. Thus it is possible to avoid any
 abnormal reduction in the internal pressure of the airbag 2. In addition,
 it is possible with such a structure to obtain exactly the same effect as
 in the first embodiment.
 With reference to FIGS. 10A and 10B; the seventh embodiment according to
 the present invention will be explained. As is shown in FIG. 10A and 10B,
 when fixing the airbag 2 and the inflator 9 to the base plate 10, instead
 of using the screw section 16, a protrusion 22 can be used. That is the
 fixing is easily achieved with the protrusion 22 and a protrusion passage
 23. The protrusion passage 23 penetrates the base plate 10 to allow
 passage of the protrusion 22.
 In the seventh embodiment constructed in this way, the protrusion 22 and
 the connector 51 are drawn out inside the base plate 10 through the
 protrusion passage 23. After that, the protrusion 22 is rotated so that
 its direction differs from that of the protrusion passage 23. In this way,
 the protrusion 22 catches on sections of the base plate 10 other than the
 protrusion passage 23 so that the inflator 9 is secured to the base plate
 10.
 The airbag 2 which holds the inflator 9 thereinto described in detail in
 the above embodiments makes it possible to eliminate the necessity for
 strongly tightening the airbag 2 between the base plate 10 and the
 inflator 9 by means of the screw section 16 and the nut 12. Therefore, it
 is possible to make use of the simple fixing mechanism described above and
 manufacture the airbag device 1 easily.
 FIGS. 11 to 13 show examples of how to simply attach the inflator 9 to the
 base plate 10.
 FIG. 11 shows an example in which the inflator 9 is made of steel and
 secured to the base plate 10 by means of a permanent magnet 24.
 FIG. 12 shows an example in which the inflator 9 is secured by simply
 screwing the screw section 16 thereof directly to the base plate 10.
 FIG. 13 shows an example in which the inflator 9 is secured to the base
 plate 10 by screwing a flange screw 25 into the inflator 9.
 The present invention is not limited to the embodiments described above but
 can be changed in various ways as described below.
 For example, in the embodiments, it was explained about the case where the
 present invention was applied to an airbag device for the driver's seat
 and the air bag device was attached to the steering unit 50. However, it
 is also possible to apply the present invention to an airbag device
 located any position inside the vehicle, such as an airbag device for a
 seat next to the driver's seat.
 Also, in order to fix the airbag 2, it is possible to fasten the airbag 2
 with bolts or the like in the vicinity of the retaining section 7. In such
 a case, even if the stress during inflation of the airbag 2 concentrates
 on the retaining section 7 retained by bolts so that the airbag 2 is
 damaged, because the area of the retaining section 7 sandwiched between
 the inflator 9 and the base plate 10 is large, the airbag 2 will not be
 detached from the base plate 10.
 Furthermore, in the fifth embodiment, the slit 17 is covered by the cover
 cloth 6. However, instead of the cover cloth 6, it is also possible to
 close up the slit 17 with, for instance, an adhesive, after inserting the
 inflator 9 into the airbag 2.
 Also, although the hole section 11 was made circular, the hole section 11
 can be formed oval in shape, corresponding to the shape of, for instance,
 the connector 51. In this case, it is possible to maintain the attachment
 strength of the airbag 2.