Abstract:
A seat belt pretensioner may include a cylinder, a piston slidably disposed in the cylinder, a gas generator installed to rear end portion of the cylinder and configured to supply a propellant gas to the piston for moving the piston in a forward direction, a first direction conversion unit disposed between the gas generator and the piston and connected to the cylinder, and a coupling member for coupling a seat belt and the piston, wherein a portion of the coupling member is engaged with the first direction conversion unit so as to change a movement direction of the coupling member while the piston moves in the forward direction, and a reward movement restriction member configured to restrict a rearward movement of the piston while the piston moves in the forward direction by the propellant gas of the gas generator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to Korean Patent Application No. 10-2008-0085442 filed Aug. 29, 2008, the entire contents of which application is incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a seat belt pretensioner which can rapidly pull in a length of a seat belt to tighten the seat belt about a vehicle occupant in case of a crash, thereby restraining and protecting the vehicle occupant. 
     2. Description of Related Art 
     In case of a crash, a vehicle occupant is moved forward through a substantial distance before a seat belt is locked by a retractor. A seat belt pretensioner functions to tighten the seat belt and protect the vehicle occupant before the forward movement of the vehicle occupant begins. 
     Referring to  FIG. 1 , a seat belt  100  is generally divided into an upper belt part  100 A and a lower belt part  100 B when viewed from a buckle tongue  110 . The upper belt part  100 A extends from the shoulder diagonally across the torso to the waist of a vehicle occupant, and the lower belt part  100 B extends laterally across the hips to restrain the waist of the vehicle occupant. A conventional seat belt pretensioner  200  shown in  FIG. 1  is installed adjacent to a buckle  300 . The seat belt pretensioner  200  is connected to the lower belt part  100 B through the engagement between the buckle tongue  110  and the buckle  300  to reduce the movement of the waist of the vehicle occupant in case of a crash. 
     The seat belt pretensioner  200  shown in  FIG. 1  is disclosed in Japanese Unexamined Patent Publication No. 2003-146184. The seat belt pretensioner  200  is structured such that a piston (not shown) disposed in a cylinder  210  is connected with the buckle  300  by a wire  220 , and a gas generator  240  is arranged in front of the cylinder  210  (in a direction facing the buckle  300 ). As the piston is fired rearward by the propellant gas generated from the gas generator  240 , the wire  220  pulls the buckle  300  and tightens the lower belt part  100 B. The gas generator  240  is installed to project vertically with respect to the cylinder  210  so as to avoid interference with the wire  220 . In  FIG. 1 , the unexplained reference numerals  230 ,  241 ,  400  and  500  respectively designate a housing, a cap, a retractor, and a center pillar. 
     The conventional seat belt pretensioner suffers from a drawback in that, since the gas generator  240  is arranged in front of the cylinder  210 , an area where the gas generator  240  is placed becomes structurally complicated, the number of parts increases, and the ease of assembly deteriorates. Also, the vertically projecting gas generator  240  interferes with surrounding parts such as a vehicle body, thereby serving as a factor that impedes the miniaturization of the pretensioner. 
     BRIEF SUMMARY OF THE INVENTION 
     Various aspects of the present invention are directed to provide a seat belt pretensioner in which a gas generator is arranged in line behind a cylinder so that the miniaturization and structural simplification of the pretensioner becomes possible. 
     In an aspect of the present invention, a seat belt pretensioner device may include a cylinder, a piston slidably disposed in the cylinder, a gas generator installed to rear end portion of the cylinder and configured to supply a propellant gas to the piston for moving the piston in a forward direction, a first direction conversion unit disposed between the gas generator and the piston and connected to the cylinder, and a coupling member for coupling a seat belt and the piston, wherein a portion of the coupling member is engaged with the first direction conversion unit so as to change a movement direction of the coupling member while the piston moves in the forward direction, and a reward movement restriction member configured to restrict a rearward movement of the piston while the piston moves in the forward direction by the propellant gas of the gas generator. 
     The seat belt pretensioner device may further include a guide member installed in the cylinder to receive a portion of the coupling member and to guide the movement direction of the coupling member while the piston moves in the forward direction. 
     The seat belt pretensioner device may further include a second direction conversion unit installed to a bracket connected to a front end portion of the cylinder and the other portion of the coupling member is engaged with the second direction conversion unit so as change the movement direction of the coupling member. 
     The second direction conversion unit may include at least a pulley rotatably coupled to the bracket and the pulley receives the other portion of the coupling member to change the movement direction of the coupling member. 
     The first direction conversion unit may include at least a pulley rotatably coupled to the cylinder and the pulley receives the portion of the coupling member to change the movement direction of the coupling member, wherein the coupling member is a wire. 
     The wire may include a first connection portion which is connected to the seat belt and a second connection portion which passes through the piston, is wound on the pulley, and is then fastened to the piston, wherein the wire has a first wire portion and a second wire portion which extend parallel to each other along the cylinder and wherein a guide member is installed in a front end portion of the cylinder and includes at least two receiving holes to receive the first wire portion and the second wire portion respectively so as to space the first and second wire portions with a constant distance therebetween. 
     The wire may include a single piece of wire which forms a loop at the first connection portion and both ends of which are fastened to the piston at the second connection portion, wherein both ends of the wire are wound on the pulley in opposite directions. 
     The wire may include one end which is connected to the seat belt and the other end which is wound on the pulley after passing through the piston in rearward, forward and rearward directions so that a loop is defined in front of the piston and is then connected to the seat belt, wherein, as the piston is fired and the loop is pulled in the forward direction, the seat belt is pulled in the rearward direction. 
     A gas guide may be disposed in front of the gas generator and has a rear opening which receives a front end of the gas generator and a plurality of gas passages which are branched from the rear opening and extend in the forward direction wherein the gas passages are aligned symmetrical in a horizontal and vertical axis in a cross-sectional view. 
     The cylinder and the gas generator may be arranged in line. 
     The reward movement restriction member may be formed in the piston, wherein the reward movement restriction member includes a roller groove formed in an outer surface of the piston, wherein a distance between the cylinder and an inner surface of the roller groove gradually decreases in the forward direction, and a roller disposed in the roller groove, wherein a front portion of the roller groove is narrower than a diameter of the roller. 
     The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description of the Invention, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a seat belt to which a conventional seat belt pretensioner is applied. 
         FIG. 2  is an exploded perspective view illustrating an exemplary seat belt pretensioner in accordance with the present invention. 
         FIG. 3  is a side sectional view of the seat belt pretensioner of  FIG. 2 . 
         FIG. 4  is a partial broken-away perspective view schematically illustrating the structure of a rear end part of the seat belt pretensioner of  FIG. 2 . 
         FIG. 5  is a transverse sectional view of the rear end part of the seat belt pretensioner of  FIG. 2 , showing the state in which a piston is moved forward by the propellant gas generated by a gas generator. 
         FIGS. 6A through 6D  are views illustrating the gas generator of the seat belt pretensioner of  FIG. 2 , wherein  FIG. 6A  is a perspective view,  FIG. 6B  is a front view,  FIG. 6C  is a side view, and  FIG. 6D  is a sectional view. 
         FIGS. 7A and 7B  are conceptual views explaining the installation or the location of a wire in the seat belt pretensioner of  FIG. 2 . 
         FIGS. 8A and 8B  are conceptual views explaining the construction of another exemplary seat belt pretensioner in accordance with the present invention, specifically, the installation or the location of a wire. 
         FIG. 9  is conceptual view explaining the construction of another exemplary seat belt pretensioner in accordance with the present invention. 
     
    
    
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
     In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
     A seat belt pretensioner in accordance with various embodiments of the present invention will be described with reference to  FIGS. 2 through 7B . Generally, the seat belt pretensioner according to various embodiments is constructed such that a seat belt (not shown) and a piston  20  disposed in a cylinder  10  are connected with each other by a wire  40 , and, when the piston  20  is fired forward by the propellant gas supplied from a gas generator  50 , the wire  40  pulls the seat belt rearward. 
     As shown in  FIGS. 2 and 3 , the cylinder  10  has a hollow configuration. A wire guide  70  is fitted into the front end of the cylinder  10  to prevent a first wire portion  40   a  and a second wire portion  40   b  of the wire  40  from becoming twisted and to hold them parallel to each other. The piston  20  is disposed adjacent to the rear end of the cylinder  10  to be movable in a forward direction. The gas generator  50  is fitted into the rear end of the cylinder  10 , and a gas guide  60  is positioned in front of the gas generator  50  so as to allow the pressure of the propellant gas to be transferred to the piston  20  without leakage. A pin  30  is placed between the piston  20  and the gas guide  60  to extend in a diametrical direction of the cylinder  10 . 
     A structure for installing or locating the wire  40  will be described with reference to  FIGS. 2 through 4 . 
     Referring to  FIG. 2 , a loop is formed on a first connection portion  41  of the wire  40 . The first connection portion  41  is connected to the seat belt, specifically, the buckle of a lower belt part. Of course, in the case that the pretensioner is installed on the anchor side of the lower belt part, the first connection portion  41  may be connected to an anchor connector or may be directly connected to the lower belt part. A second connection portion  42  of the wire  40  passes through the piston  20 , is wound on the pin  30 , and is then fastened to the piston  20 . 
     Referring to  FIGS. 3 and 4 , the first wire portion  40   a  and the second wire portion  40   b , which form loops at the second connection portion  42 , pass through the wire guide  70  and the piston  20 , and extend in parallel between the wire guide  70  and the piston  20  while being separated up and down from each other. The upwardly positioned first wire portion  40   a  passes through the right upper portion of the piston  20 , is wound on the pin  30  in the clockwise direction (when viewed in  FIG. 4 ), passes through the right lower portion of the piston  20 , and is then fastened to the front surface of the piston  20  by a wire fastener  21 . The downwardly positioned second wire portion  40   b  passes through the left lower portion of the piston  20 , is wound on the pin  30  in the counterclockwise direction (when viewed in  FIG. 4 ), passes through the left upper portion of the piston  20 , and is then fastened to the front surface of the piston  20  by the wire fastener  21 . The first wire portion  40   a  and the second wire portion  40   b  are placed symmetrically to each other. 
     The structure for installing the wire  40  as described above can be clearly understood from the conceptual views of  FIGS. 7A and 7B . First, as shown in  FIGS. 7A and 7B , it is to be noted that the wire  40  is composed of a single piece of wire. The middle portion of the wire  40  is flexed and forms the loop L. Both ends E of the wire  40  are wound on the pin  30  in opposite directions (indicated by the arrows A and B) and are fastened to the piston  20 . If the piston  20  to which both ends E of the wire  40  are fastened is pushed forward, as the loop L and both ends E of the wire  40  approach each other, the seat belt can be pulled rearward by the wire  40 . 
     Unlike the illustration of  FIGS. 7A and 7B , it is to be understood that one of the first wire portion  40   a  and the second wire portion  40   b  wound on the pin  30  may be removed. That is to say, as shown in  FIG. 9 , it is conceivable that the front end of a single piece of wire  40  is connected to the buckle, and the rear end thereof passes through the piston  20 , is wound on the pin  30  and is then fastened to the piston  20 . 
     Meanwhile, as shown in  FIG. 4 , two pulleys  31  can be installed on the pin  30  to be rotated about the pin  30 , and the wire  40  can be wound on these pulleys  31 . The pulleys  31  allow the propellant force applied to the piston  20  to be transferred to the wire  40  without loss. 
     A restriction mechanism for restricting the rearward movement of the piston  20  will be described with reference to  FIGS. 3 and 4 . 
     The piston  20  should be moved only in the forward direction, and the rearward movement of the piston  20  should be restricted. The rearward movement of the piston  20  means a decrease in the force for the wire  40  to pull the seat belt, and this means in turn failure in restrang a vehicle occupant by the seat belt pretensioner. Therefore, the restriction mechanism for permitting the movement of the piston  20  only in the forward direction needs to be provided between the piston  20  and the cylinder  20 . 
     In order to constitute the restriction mechanism, rollable elements such as balls and rollers are employed. In detail, as shown in  FIG. 4 , rollers  23  are interposed between the cylinder  10  and the piston  20 . Roller grooves  22  are defined on both sides of the piston  20  on which the rollers  23  are provided, such that the depth of the roller grooves  22  gradually decreases in the forward direction. Due to this fact, if the piston  20  is moved rearward, the rollers  23  roll and move forward to be caught tight between the piston  20  and the cylinder  10 , by which the rearward movement of the piston  20  is prevented. In  FIG. 4 , the piston  20  is illustrated by a single-dotted line. 
     The structure of the gas guide  60  will be described below with reference to  FIGS. 5 and 6A  through  6 D. 
     Referring to  FIG. 5 , the gas guide  60  is installed close to the pin  30  such that the propellant gas generated from the gas generator  50  can be quickly transferred to the piston  20 . Elements are defined on the front end of the gas guide  60  in order to prevent interference with the pin  30 , the pulleys  31  and the wire  40 . The front end of the gas guide  60  is defined with pin receiving grooves  63  in the horizontal direction and wire receiving grooves  64  in the vertical direction. 
     Referring to  FIGS. 6A and 6B , in addition to these grooves  63  and  64 , gas passages  61  are defined on the front end of the gas guide  60  to allow the propellant gas from the gas generator  50  to be transferred to the piston  20  through bypassing the pin  30 , the pulleys  31  and the wire  40 . As can be readily seen from  FIGS. 6C and 6D , these gas passages  61  branch from a rear opening  62  which is defined in the rear end of the gas guide  60  to receive the front end of the gas generator  50 , in such a way as to extend in various directions. An O-ring  24  is placed on the rear end of the piston  20  such that the propellant gas supplied through the gas guide  60  does not leak through a gap between the piston  20  and the cylinder  10  (see  FIG. 5 ). 
     Referring to  FIGS. 2 and 3 , a bracket  80  is provided in front of the wire guide  70 . The wire  40  is bent upward in the bracket  80 . In detail, the wire  40  is bent upward while passing between a first pin  81  and a second pin  82  which are secured to the bracket  80  in the horizontal direction. However, the bracket  80  is not an essential component. As the case may be, the wire  40  may not be bent upward and may be linearly connected to the seat belt. In particular, this is the case when the seat belt pretensioner is installed on the anchor side of the lower belt part. 
     Referring to  FIGS. 8A and 8B , another exemplary embodiment is different from the above-described embodiment in terms of the structure for installing or locating a wire. The other construction is essentially the same as that of the above described embodiment. According to this and other embodiments of the present invention, both ends E of the wire  40  are connected to the seat belt, and the loop L is formed in front of the piston  20  by the middle portion of the wire  40 . In detail, one end E 1  of the wire  40  is connected to the seat belt. The other end E 2  of the wire  40  passes through the piston  20  in the rearward direction, is primarily wound on the pin  30 , forms the loop L after passing through the piston  20  in the forward direction, is secondarily wound on the pin  30  by passing through the piston  20  in the rearward direction, and is then connected to the seat belt after passing through the piston  20  in the forward direction. The directions, in which the wire  40  is primarily and secondarily wound on the pin  30 , are the same with each other as indicated by the arrows B. 
     Describing the wire installation structure according to various embodiments using the first connection portion and the second connection portion (see  FIG. 2 ) as described above, both ends E of the wire  40  constitute the first connection portion which is connected to the seat belt, and the loop L is formed on the second connection portion of the wire  40  which is connected to the piston  20 . If the piston  20  is moved forward by the pressure of the propellant gas generated from the gas generator  50  while pulling the loop L, as the distance between the first connection portion and the second connection portion is shortened, the seat belt is pulled rearward. 
     However, the present invention is not restricted to the structure including the first connection portion and the second connection portion that is coupled by the first and wire portion as aforementioned above. In further embodiments, the first connection portion and the second connection portion can be coupled by a single wire portion not to form a loop. 
     As is apparent from the above description, the seat belt pretensioner according to the present invention provides advantages in that, since a gas generator can be arranged in line behind a cylinder, the miniaturization and structural simplification of the seat belt pretensioner becomes possible. 
     Also, because the degree of freedom in designing the seat belt pretensioner increases, the number of parts can be decreased, and the ease of assembly and space utilization efficiency can be improved. 
     For convenience in explanation and accurate definition in the appended claims, the terms “front”, “rear”, “forwards” and “rearwards” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
     The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.