Patent Publication Number: US-2002000487-A1

Title: Seat belt retractor

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to a seat belt retractor with a pretensioner. More particularly, the present invention relates to a seat belt retractor with a pretensioner that includes balls positioned in a pipe.  
       [0002] A passenger car is normally equipped with seat belt devices for protecting occupants when the car experiences an abrupt deceleration. Such a seat belt device may include a pretensioner which takes up a seat belt around an occupant to restrain the occupant with increased forces when an accident such as a vehicle collision is detected.  
       [0003] There are various types of pretensioners. One known type of pretensioner comprising a pipe, a gas generator disposed on one end of the pipe, a piston arranged in the pipe, and balls arranged within the pipe. Typically, the balls are moved by the piston as a result of gas pressure produced by the gas generator. The balls are discharged through an outlet disposed at the other end of the pipe, and a pretensioner gear and a gear connected to a spool are meshed with each other and rotated by the balls being discharged, thereby pretensioning a seat belt.  
       [0004] A significant problem in pretensioners of this type is that force created by gas pressure is absorbed by friction between the inner wall of the pipe and the balls, thus reducing force to be transmitted to the gear. Therefore, in order to obtain large pretensioning force, previous device had a large configuration. The large device creates additional problems, because it is difficult to install a large retractor in a passenger car.  
       SUMMARY OF THE INVENTION  
       [0005] The present invention was made taking the aforementioned circumstances into consideration and the object of this invention is to provide a seat belt retractor with a pretensioner which can effectively transmit gas pressure produced form a gas generator to a gear, in order to obtain large pretensioning force, without requiring a retractor of increased size.  
       [0006] The aforementioned object is achieved according to the present invention by providing a seat belt retractor with a pretensioner of a type comprising a pipe, a gas generator disposed on one end of the pipe, a piston arranged in the pipe, and balls arranged within the pipe, in which the balls are moved via the piston by gas pressure produced by the gas generator and are discharged through an outlet disposed at the other end of the pipe, and a pretensioner gear and a gear connected to a spool are meshed with each other and rotated by the balls being discharged, thereby pretensioning a seat belt, the seat belt retractor being characterized in that lubricant of a type forming a dry lubricating film is applied to at least either the inner surface of said pipe or the outer surfaces of said balls.  
       [0007] According to the present invention, since the lubricant of a type forming a dry lubricating film is applied to at least either the inner surface of the pipe or the outer surfaces of the balls, the friction resistance between the inner surface of a pipe and balls can be reduced, thereby effectively transmitting gas pressure produced by the gas generator to a seat belt retracting mechanism. Further, since the lubricant is not of a wet type, there is no possibility of the lubricant leaking out and of thus causing a trouble.  
       [0008] According to the present invention, the dry coating lubricant may include a rust preventing property in addition to the lubricating property. Because the seat belt retractor is used over a long term of years, the pipe and the balls should be treated with a rust-preventive process. Since the dry coating lubricant has rust preventing property besides its lubricating property, the rust-preventive process and the lubrication process can be done simultaneously, thereby simplifying the manufacturing process.  
       [0009] As an alternative, grease may be employed instead of the dry lubricant. As mentioned above, when lubricant of a wet type is used, there is normally some concern that the lubricant will leak and thus causes a problem. However, if there is no possibility of such trouble, grease can exhibit the same effect as the dry coating lubricant.  
       [0010] According to the present invention, preferably, the lubricant is of a type capable of exhibiting its performance enough even at a temperature higher than 100° C. Since the temperature of the gas produced at the start of the pretensioner is very high, the temperature of the balls may become 100° C. or more. Even in such a case, gas pressure produced by the gas generator can be effectively transmitted to a seat belt retracting mechanism.  
       [0011] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012] These and other features, aspects and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.  
     [0013]FIG. 1 is a sectional view showing an example of structures of a pretensioner.  
     [0014] FIGS.  2 ( 1 )- 2 ( 4 ) are views showing the operation of the pretensioner shown in FIG. 1.  
     [0015]FIG. 3 is an exploded perspective view showing an example of a seat belt retractor having the pretensioner.  
    
    
     DETAILED DESCRIPTION  
     [0016]FIG. 3 is an exploded perspective view showing a seat belt retractor with a ball type pretensioner. This seat belt retractor comprises a base frame  1 , a spool  2  housed in the base frame  1 , and a seat belt (not shown) wound onto the spool  2 . Therefore, the rotation of the spool  2  causes the winding and unwinding of the seat belt. The spool  2  has a torsion bar  3  as its shaft, one end of the torsion bar  3  is supported in a retainer  6  via two locking mechanisms  4 ,  5 .  
     [0017] The spool  2  has a gear  7  on one end thereof. The spool gear  2  meshes with a gear in a return spring cover  8 . As a result, the spool  2  is biased in a belt-winding direction by a return spring in the return spring cover  8 .  
     [0018] The seat belt retractor having the aforementioned structure is provided with a pretensioner. Hereinafter, the structure of the pretensioner will be described. The pretensioner comprises a pipe  11  between a pretensioner cover  9  and a pretensioner plate  10 , and a gas generator  12  disposed on end of the pipe  11 . Arranged inside the pipe  11  are a stopper spring  13 , a piston  14 , and a plurality of balls  15 . The pipe  11  has a cut-out in a peripheral portion near the other end thereof and a guide block  16  is fitted into the other end of the pipe  11 .  
     [0019] The pretensioner cover  9  is provided with two pins  17  by which a ring gear  18  (i.e., “the pretensioner gear”) is held. The front-most ball  15   a  is supported between one of the external teeth of the ring gear  18  and a portion of the inner wall of the pipe  11  facing to the cut-out.  
     [0020] On the other hand, a pinion  20  (i.e., “the gear connected to the spool”) is arranged to be connected to the gear  19  of the spool  2 . In the normal state, the ring gear  18  and the pinion  20  are not meshed with each other. When gas is produced by the gas generator  12 , however, the balls  15  are pushed via the piston  14  by the pressure of gas so that the pins  17  are sheared by forces from the balls, whereby the ring gear  18  is released to be free and thus moves to be meshed with the pinion  20 , as will be described in detail later. The ring gear  18  in this state is forced to be rotated by the balls  15  so as to rotate the spool  2  via the pinion  20 . In this manner, the seat belt is pretensioned.  
     [0021]FIG. 1 is a sectional view showing an embodiment of the pretensioner according to the present invention. The front-most ball  15   a  is stopped by one of external teeth  18   a  of the ring gear  18  held by the pins  17  shown in FIG. 3. Other balls  15  are retained in the pipe  11  because the front-most ball  15   a  is stopped. The piston  14  is spherical and is in contact with the rear-most ball  15   b . The piston  14  is biased by the spring  13  so as to press the balls  15  toward the front end. Preferably, the balls  15  are made of steel and the piston  14  is made of silicone resin.  
     [0022] The pipe  11  has a cut-out formed in a portion near the outlet of the balls  15 , in which a portion of the ring gear  18  is positioned. Fitted in the front end of the pipe  11  is a guide block  16 , preferably made of aluminum. The guide block  16  is fixed to a supporting plate  21  by a vise  22 . It should be noted that the vise  22  also has the function of fixing the pipe  11  to the supporting plate  21 . Numeral  23 ,  24  designate sections of the pretensioner cover  9 . The section  23  positions the pipe  11  and the section  24  forms a ball receiving portion  25 .  
     [0023] In this state, the ring gear  18  is held by the pins  17  shown in FIG. 3, the internal teeth  20   b  of the pinion  20  are fitted into the gear  19  of the spool  2 , and the internal teeth  18   b  of the ring gear  18  are meshed with none of the external teeth  20   a  of the pinion  20 . Therefore, the pretensioner in this state has no effect on the rotation of the spool.  
     [0024] As gas is produced by the gas generator  12 , the piston  14  is pushed by the pressure of gas. The force on the piston  14  is transmitted to the balls  15  so that the front-most ball  15   a  exerts force on the external tooth  18   a  of the ring gear  18 . As a result of this, the pins  17  shown in FIG. 3 are sheared so as to release the ring gear  18 . Therefore, the ring gear  18  moves to the lower right in FIG. 1 because the ball  15  exerts force on the ring gear  18  to the lower right direction. This movement brings the internal teeth  18   b  of the ring gear  18  to be meshed with the external teeth  20   a  of the pinion  20 .  
     [0025] In this condition, a space is created between the inner surface of the pipe  11  and each bottom between the adjacent external teeth  18   a  of the ring gear  18  through which the ball  15  can pass. The pushed ball  15  passes through the space while rotating the ring gear  18 , and falls down to the ball receiving portion  25 . Then, the next ball  15  presses another external tooth  18   a  of the ring gear  18  so as to further rotate the ring gear  18 , and falls down to the ball receiving portion  25 . The guide block  16  is provided to maintain the distance between the guide block  16  and the bottoms of the ring gear  18  slightly greater than the diameter of the balls  15 . That is, the guide block  16  has the function of enlarging the range in which the balls  15  and the ring gear  18  are in contact.  
     [0026] The aforementioned actions are shown in FIGS.  2 ( 1 )- 2 ( 4 ). FIG. 2( 1 ) illustrates the initial state. FIG. 2( 2 ) illustrate the state where the pins  17  are sheared to release the ring gear so that the internal teeth  18   b  of the ring gear and the external teeth  20   a  of the pinion  20  are meshed. FIGS.  2 ( 3 ),  2 ( 4 ) illustrate the state where the ring gear  18  and the pinion  20  are rotated by pushing force of the balls.  
     [0027] Hereinafter, a preferred embodiment of the present invention will be described with reference to FIG. 1. Lubricant of a type forming a dry lubricating film (hereinafter, referred to as “dry coating lubricant”) is sprayed to the inner surface of the pipe  11  and the outer surfaces of the balls  15  shown in FIG. 1. Preferably, a molybdenum coating should be employed as the lubricant. As an example of the dry coating lubricant, Solvest® of a type forming a dry lubricating film available from SST INC. is preferably used. Since this lubricant has rust preventing property besides the lubricating property, the use of this lubricant can eliminate the rust-preventive process such as plating. In addition, since the lubricant has a wide usable temperature range from −200° C. to 500° C., the lubricant can exhibit its performance enough even when the pipe  11  and the balls  15  are heated to a high temperature by gas produced by the gas generator  12 .  
     [0028] If melting of grease causes no trouble because of a specific structure of the pretensioner, grease can be employed instead of the dry coating lubricant.  
     [0029] As described above, according to the present invention, the friction resistance between the inner surface of a pipe and balls can be reduced, thereby effectively transmitting gas pressure produced by a gas generator to a seat belt retracting mechanism and thus achieving a compact retractor. Since the lubricant is not of a wet type, there is no possibility of the lubricant leaking out and of thus causing a trouble.  
     [0030] In an aspect according to the present invention, the rust-preventive process and the lubrication process can be done simultaneously, thereby simplifying the manufacturing process.  
     [0031] In an aspect according to the present invention, even when the pipe and/or the balls become hot due to the temperature of gas, gas pressure produced by the gas generator can be effectively transmitted to a seat belt retracting mechanism.  
     [0032] Given the disclosure of the present invention, one versed in the art would appreciate that there may be other embodiments and modifications within the scope and spirit of the invention. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is to be defined as set forth in the following claims.  
     [0033] The priority document Japanese Patent Application No. 2000-118001, filed Apr. 19, 2000 is hereby incorporated by reference herein in its entirety.