Abstract:
An assembly structure of an airbag case includes a steering wheel core mounted to a hub of a steering wheel, the hub having an open top part and a retainer attached to the steering wheel core that retains an airbag and an inflator supplying a high-pressure gas to the airbag. An airbag cover is disposed on the hub of the steering wheel so that the airbag cover covers the open top part of the hub of the steering wheel and has a tear line formed thereat, the airbag cover being severed along the tear line when the airbag is expanded, and a plurality of hooks are formed at the edge of the airbag cover.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an airbag device for vehicles, and more particularly to an assembly structure of an airbag case wherein the edge of an airbag cover is hooked on a steering wheel, and a retainer is attached to a steering wheel core by means of bolts. 
   2. Description of the Related Art 
   Generally, an airbag device is a device mounted to a steering wheel of a vehicle for protecting a driver from injury when a collision of the vehicle occurs. Also, the airbag device is mounted to the steering wheel in such a manner that it is vertically moved, whereby the airbag device serves to turn on/off a horn switch mounted in the steering wheel. 
     FIG. 1  is a perspective view showing a conventional assembly structure of an airbag case, and  FIG. 2  is a side view, in section, of the conventional assembly structure of the airbag case. 
   As shown in  FIGS. 1 and 2 , the conventional airbag device for vehicles comprises: an airbag case  10  to  13  mounted to a hub  2  of a steering wheel  1 ; an inflator  14  for supplying a high-pressure gas when a vehicle collision is detected by means of an impact sensor; and an airbag  16  expanding toward a passenger when the gas is supplied from the inflator  14  to the airbag  16 . 
   The hub  2  of the steering wheel  1  is formed in such a manner that the width of the hub  2  is gradually increased from the lower part thereof to the upper part thereof. The hub  2  has an open top part and a bottom part, through which a hub hole  2 A is formed. Inside the hub  2  is mounted a steering wheel core  4 , which is extended to a rim  3  of the steering wheel  1 . 
   The airbag case  10  to  13  comprises: an airbag cover  10  for covering the open top part of the hub  2  of the steering wheel  1 ; a retainer  11  disposed on the steering wheel core  4  for retaining the inflator  14  and the airbag  16 ; a rib  12  protruded from the airbag cover  10  in such a manner that the rib  12  surrounds the retainer  11 , the rib  12  being attached to the retainer  11  by means of rivets  20 ; and brackets  13  attached to the rib  12  and the retainer  11  by means of the rivets  20  and attached to the steering wheel core  4  by means of bolts  22 . 
   At the airbag cover  10  is formed a tear line  17 . More specifically, the tear line  17  is formed at the rib-inside area  10 A of the airbag cover  10 , which is placed inside the rib  12 . Consequently, the airbag cover  10  is severed along the tear line  17  when the airbag  16  is expanded. 
   The retainer  11  is mounted coaxially with the airbag cover  10 . In other words, the retainer  11  and the airbag cover have the same central axis C. The width  11 W of the retainer  11  is approximately ½ of the width  10 W of the airbag cover  20 . The rib  12  is formed halfway between the central axis C and the edge of the airbag cover  10  so that the rib  12  comes in contact with a sidewall  11 A of the retainer  11 . Consequently, the rib-inside area  10 A of the airbag cover  10 , which is placed inside the rib  12 , corresponds exactly to the area where the tear line is formed. In other words, the area of the airbag cover  10  within the tear line  17  is approximately ½ of the area of the entire airbag cover  10 . 
   The operation of the conventional assembly structure of the airbag case with the above-stated construction will now be described. 
   When a vehicle collision is detected by means of the impact sensor, the high-pressure gas is supplied from the inflator  14  to the airbag  16 . As the gas is filled in the airbag  16 , the airbag  16  is expanded so that the airbag cover  10  is severed along the tear line  17 , and is then fully expanded toward a passenger. 
   In the conventional assembly structure of the airbag case, the shape of the tear line  17  is experimentally designed since the expansion performance of the airbag  16  is affected by the shape of the tear line  17 . However, the area of the airbag cover  12  within the tear line  17  is limited to approximately ½ of the area of the entire airbag cover  10  due to the rib  12 . Consequently, the expansion performance of the airbag  16  may be improved only restrictively. 
   To the airbag cover  10  is mounted a membrane type horn switch  18 , by which a horn sounding an alarm is operated. The horn switch  18  is disposed inside the rib  12  so that interference between the horn switch  18  and the rib  12  is prevented. As a result, an area in which the horn switch  18  can be disposed and operated is limited. 
   The conventional assembly structure of the airbag case provides no additional supporting member for supporting the edge of the airbag cover  10 . As a result, the edge of the airbag cover  10  is loosened from the steering wheel  1 , which leads to poor appearance. The rib  12  is formed at a distance from the edge of the airbag cover  10 , and therefore the edge of the airbag cover  10  in not securely and reliably supported by the rib  12 . 
   In the conventional assembly structure of the airbag case, the rib  12 , the retainer  11 , and the brackets  13  are fastened together by means of the rivets  20 , and then the brackets  13  are attached to the steering wheel core  4  by means of the bolts  22 . In this way, the airbag case  10  to  13  is assembled with the steering wheel  1 , whereby the number of the parts to be assembled is large, additional tools for rivet  20  and bolt  22  works are required, and thus the cost and time of assembly are increased. 
   SUMMARY OF THE INVENTION 
   Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an assembly structure of an airbag case wherein an area defined by a tear line is large and thus an operation area of a horn switch is large, its assembly operation is simplified, and its external appearance is appealing and smooth. 
   In accordance with the present invention, the above and other objects can be accomplished by the provision of an assembly structure of an airbag case, comprising: a steering wheel core mounted to a hub of a steering wheel, the hub having an open top part; a retainer attached to the steering wheel core for retaining an airbag and an inflator supplying a high-pressure gas to the airbag; an airbag cover disposed on the hub of the steering wheel so that the airbag cover covers the open top part of the hub of the steering wheel and having a tear line formed thereat, the airbag cover being severed along the tear line when the airbag is expanded; and hooks formed adjacent the edge of the airbag cover, wherein the airbag cover is securely fixed to the steering wheel by the hooks. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a perspective view showing a conventional assembly structure of an airbag case; 
       FIG. 2  is a side view, in section, of the conventional assembly structure of the airbag case; 
       FIG. 3  is a side view, in section, of an assembly structure of an airbag case according to a first preferred embodiment of the present invention; and 
       FIG. 4  is a side view, in section, of an assembly structure of an airbag case according to a second preferred embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Now, a first preferred embodiment of the present invention will be described in detail with reference to  FIG. 3 . 
     FIG. 3  is a side view, in section, of an assembly structure of an airbag case according to a first preferred embodiment of the present invention. 
   The assembly structure of the airbag case according to the first preferred embodiment of the present invention comprises a steering wheel core  54  mounted to a hub  52 , which has an open top part, of a steering wheel  50 . To the steering wheel core  54  is attached a retainer  64  for retaining an airbag  60  and an inflator  62 . On the hub  52  of the steering wheel  50  is disposed an airbag cover  66 , which covers the open top part of the hub  52  of the steering wheel  50 . Adjacent the edge of the airbag cover  66  are formed hooks  70 , which are vertically extended toward the hub  52  of the steering wheel  50 . The airbag cover  66  is fitted with the upper sidewall of the steering wheel  50  by the hooks  70  adjacent the edge thereof. 
   The hub  52  of the steering wheel  50  is formed in such a manner that the width of the hub  52  is gradually increased from the lower part thereof to the upper part thereof. The hub  52  has a bottom part through which a hub hole  52 A is formed. The steering wheel core  54  comprises: a horizontal panel  54 A disposed in parallel with the bottom surface of the hub  52  of the steering wheel  50  while the horizontal panel  54 A is spaced a prescribed distance from the bottom surface of the hub  52  of the steering wheel  50 , the horizontal panel  54 A comprising a lower horizontal panel part, an upper horizontal panel part, and an inclined connection part  54 S; and a plurality of inclined panels  54 C formed integrally with the upper horizontal panel part of the horizontal panel  54 A. The inclined panels  54 C are inclined upwardly and outwardly. Each of the inclined panels  54 C has an upper end  54 B bent outwardly with slow curvature. The upper ends  54 B of the inclined panels  54 C are inserted into core holes  56 A formed at a rim  56  of the steering wheel  50 , respectively. 
   At the upper ends  54 B of the inclined panels  54 C are formed hook holes  57 , through which the hooks  70  of the airbag cover  66  are vertically inserted, respectively. Preferably, the hook holes  57  are vertically formed so that the hooks  70  are easily inserted through the hook holes  57 , respectively. 
   The retainer  64  comprises: a top retainer part  64 A disposed above the horizontal panel  54 A of the steering wheel core  54  while the top retainer part  64 A is disposed in parallel with the horizontal panel  54 A of the steering wheel core  54 , the top retainer part  64 A having a hole formed at the central area thereof, through which the inflator  62  is inserted so that the inflator  62  is fitted in the hole of the top retainer part  64 A; and a sidewall  64 B formed in the shape of a ring from the edge of the top retainer part  64 A toward the horizontal panel  54 A of the steering wheel core  54  so that the sidewall  64 B of the retainer  64  is disposed on the inclined connection part  54 S of the horizontal panel  54 A of the steering wheel core  54 . To the top retainer part  64 A of the retainer  64  is attached the airbag  60  by means of bolts. 
   At the retainer is integrally formed a flange  65 , which is inwardly bent from the lower end of the sidewall  64 B of the retainer  64  toward the inside of the retainer  64  in such a manner that the flange  65  comes in surface contact with the horizontal panel  54 A of the steering wheel core  54 . 
   The flange  65  comprises: an inclined panel  65 A formed at the lower end of the sidewall  64 B of the retainer  64  while the inclined panel  65 A is bent at a prescribed angle so that the inclined panel  65 A comes in contact with the inclined connection part  54 S of the horizontal panel  54 A of the steering wheel core  54 ; and a horizontal panel  65 B inwardly extended from the end of the inclined panel  65 A while the horizontal panel  65 B is in parallel with the horizontal panel  54 A of the steering wheel core  54  so that the horizontal panel  65 B comes in contact with the lower horizontal panel part of the horizontal panel  54 A of the steering wheel core  54 . 
   At the horizontal panel  65 B of the flange  65  is formed at least one first bolt hole  65 C. Similarly, at the horizontal panel  54 A of the steering wheel core  54  is formed at least one second bolt hole  54 D, which vertically corresponds to the first bolt hole  65 C of the horizontal panel  65 B of the flange  65 . Through not only the first bolt hole  65 C but also the second bolt hole  54 D is inserted a bolt B, by which the retainer  64  is securely fixed to the steering wheel core  54 . 
   Each of the hooks  70  is preferably made of a plastic material with an elastic force so that the hooks  70  are easily engaged with or disengaged from the corresponding hook holes  57  by the elastic force. Each of the hooks  70  comprises: a supporting protrusion  74  provided adjacent the edge of the airbag cover  66  and vertically extending toward the hub  52  of the steering wheel  50 , the supporting protrusion  72  being inserted through the corresponding hook hole  57 ; and a hooking end  74  formed at the end of the supporting protrusion  72 , the hooking end  74  being inserted through the corresponding hook hole  57  by the elastic force and caught by the steering wheel core  54 . 
   At the airbag cover is formed a tear line  67 , by which the airbag cover is easily severed when the airbag  60  is expanded. As described above, the hooks  70  are formed adjacent the edge of the airbag cover  66 . Consequently, an area of the airbag cover  66  where the tear line  67  is formed is considerably increased as compared to the aforesaid conventional art. In other words, the area of the airbag cover  66  within the tear line  67  approximately corresponds to the area of the entire airbag cover  66 . 
   To the lower surface of the airbag cover  66  is mounted a membrane type horn switch  80 , which is elastically deformed in the lower direction to be switched on when a driver pushes down the airbag cover  66 . The airbag cover  66  is elastically deformed with the hooks as supporting points. As described above, the hooks are formed adjacent the edge of the airbag cover  66  according to the present invention. Consequently, an area in which the membrane type horn switch  80  can be disposed and operated is considerably increased as compared to the conventional art. 
   The airbag cover  66  is made of a plastic material with an elastic force. Consequently, the airbag cover  66  is elastically deformed in the lower direction when the airbag cover  66  is pushed down so that the membrane type horn switch  80  is turned on, and is restored to the original state when the pushing operation of the airbag cover  66  is stopped so that the membrane type horn switch  80  is turned off. Preferably, not only the airbag cover  66  but also the hooks  70  are made of a plastic material with an elastic force. 
   The airbag cover  66  is securely supported while the airbag cover  66  is not loosened adjacent the edge thereof from the steering wheel  50  since the hooks  70  are formed adjacent the edge of the airbag cover  66 . 
   The assembly operation of the airbag case with the above-stated construction according to the present invention will now be described. 
   First, the retainer  64  is disposed inside the hub  52  of the steering wheel  50  so that the first bolt hole  65 C of the horizontal panel  65 B of the flange  65  vertically corresponds to the second bolt hole  54 D of the horizontal panel  54 A of the steering wheel core  54 , and then the bolt B is inserted through the first and second bolt holes  65 C and  54 D. In this way, the retainer is mounted to the steering wheel core  54 . 
   Next, the inflator  64  and the airbag  62  are attached to the retainer  64 , and then the airbag cover  66  is pushed toward the hub  52  of the steering wheel  50 . As a result, the hooks  70  are inserted through the hook holes  57 , respectively, by which the airbag cover  66  is fitted with the steering wheel core  54 . Consequently, the assembly operation of the airbag case is completed. 
     FIG. 4  is a side view, in section, of an assembly structure of an airbag case according to a second preferred embodiment of the present invention. The assembly structure according to the second preferred embodiment of the present invention is very similar to that according to the first preferred embodiment of the present invention, and thus only the detailed description of the difference between the second preferred embodiment of the present invention and the first preferred embodiment of the present invention will be given. 
   As shown in  FIG. 4 , the assembly structure of the airbag case according to the second preferred embodiment of the present invention comprises a retainer  110  mounted to a core  100  of a steering wheel by bolts  104 . To a hub  106  of the steering wheel is attached an airbag cover  112 . Adjacent the edge of the airbag cover  112  are formed hooks  114 , which are protruded from the edge of the airbag cover  112  toward a rim  108  of the steering wheel. The hooks  114  are fitted into hook holes  108 A formed at the rim  108  of the steering wheel so that the airbag cover  112  is fixed to the steering wheel. 
   As apparent from the above description, the present invention provides an assembly structure of an airbag case wherein a retainer is attached to a steering wheel core by bolts, and hooks formed adjacent the edge of an airbag cover are inserted through hook holes formed at the upper part of a steering wheel so that the airbag cover is fixed to the steering wheel, whereby the number of the parts to be assembled is decreased, the assembly operation is simplified, and thus the cost of assembly is reduced. 
   According to the present invention, the airbag cover is securely supported while the airbag cover is not loosened adjacent the edge thereof from the steering wheel since the hooks are formed adjacent the edge of the airbag cover, whereby its external appearance is appealing and smooth. 
   Furthermore, a tear line can be formed in such a manner that the area of the airbag cover within the tear line approximately corresponds to the area of the entire airbag cover since the hooks are formed adjacent the edge of the airbag cover, whereby the tear line can be designed in various ways, and thus the expansion performance of an airbag is improved. 
   According to the present invention, a membrane type horn switch can be mounted to the airbag cover over the entire area of the airbag cover since the hooks are formed adjacent the edge of the airbag cover, whereby design of the membrane type horn switch is not restricted, an operation area of the membrane type horn switch is increased, and thus the membrane type horn switch can be conveniently operated. 
   Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.