Pretensioner for webbing retractor

Abstract: A pretensioner (10) for a webbing retractor (38) is provided with a cylinder into which gas is supplied thereby moving a piston. A rack thus causes a pinion (18) to rotate which causes a webbing (16) to be wound onto a winding shaft (14). During the assembly process for the pretensioner, an O-ring (34) is fitted onto a seal holding portion (32) of a piston (28) and the O-ring and piston are inserted together into a cylinder (20). Therefore, the conventional cutting process for forming a seal holding groove is unnecessary. In a normal state, the piston does not come into direct contact with the bottom portion of the cylinder, as in a conventional apparatus, instead the O-ring abuts the bottom portion of the cylinder. Therefore, noise generated by the bottom of the cylinder coming into contact with the piston due to vibration and the like can be prevented.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a pretensioner for a webbing retractor which removes the slackness in a webbing by forcefully winding the webbing onto a winding shaft when a vehicle executes emergency deceleration in a collision or the like. Description of the Related Art A webbing retractor is provided with a pretensioner for removing the slackness in a webbing by forcefully winding the webbing onto a winding shaft when a vehicle executes emergency deceleration in a collision or the like. This type of pretensioner includes what is known as a rack and pinion type of pretensioner which is provided in the webbing retractor 50 shown in Fig. 5. This webbing retractor 50 is provided with a pinion 56 which is connected to a winding shaft 60 onto which the webbing 58 is wound so as to always rotate integrally with the winding shaft 60. A cylinder 52 is provided near the pinion 56 so that when the vehicle executes an emergency deceleration, gas is supplied to the inside of the cylinder 52. A piston 62 is provided so as to be movable inside the cylinder 52. When the vehicle executes an emergency deceleration, the piston 62 is moved by the pressure of the gas in the direction of the arrow C shown in Fig. 5. A rack 64 is provided integrally with the piston 62 on the surface thereof nearest the pinion 56. The rack 64 is provided so as to move together with the piston 62 thereby meshing with the pinion 56 and causing the pinion 56 to rotate in the direction in which the webbing 58 is retracted (the direction shown by the arrow A in Fig. 5). Accordingly, in an emergency deceleration of the vehicle, the webbing 58 is wound onto the winding shaft 60 and the slackness in the webbing 58 is removed. The piston 62 is positioned in its initial position by abutting the bottom portion 66 of the cylinder 52. A seal holding groove 68 is formed in the side surface of the piston 62 by cutting the side surface of the piston 62 and an elastic O ring 70 is mounted in the seal holding groove 68. The O ring 70 seals the gap between the piston 62 and the inner wall 72 of the cylinder 52 thereby increasing the air-tightness between the piston 62 and the cylinder 52. It should be noted that in this type of webbing retractor 50, costs are increased because of the labor required by the cutting process for forming the seal holding groove 68 and stretching the O ring 70 to fit into the seal holding groove 68 is difficult. Because of this, in, for example, the webbing retractor 80 described in Japanese Patent Application Laid Open (JP-A) 9-202213 (refer to Fig. 6), the piston 82 has a structure where a piston body 84 and a pressure receiving plate 86 are formed separately and an O ring 88 is sandwiched between the piston body 84 and the pressure receiving plate 86. Because the O ring 88 is sandwiched between the piston body 84 and the pressure receiving plate 86, this webbing retractor 80 does not require the cutting process to form the seal holding groove 68 or the task of fitting the O ring 70 into the seal holding groove 68. However, because the piston 82 of the webbing retractor 80 has a structure where a piston body 84 and a pressure receiving plate 86 are formed separately, the number of parts is increased thereby leading to increased costs. Moreover, there is a drawback in that a noise from the contact is generated when the bottom portion 66 of the cylinder 52 comes into contact with the pressure receiving plate 86 of the piston 82 due to vibration and the like. Moreover, if the webbing retractor 50 shown in Fig. 5 is provided with what is known as a force limiter mechanism to prevent the load on a vehicle occupant from rising above a predetermined value when the vehicle executes an emergency deceleration, then when the force limiter operates, the pinion 56 rotates in the opposite direction to the direction in which the webbing 58 is retracted (the direction shown by the arrow B in Fig. 5) thus causing the piston 62 to move towards the bottom portion 66 of the cylinder 52 (the direction shown by the arrow D in Fig. 5) and to abut the bottom portion 66 of the cylinder 52. Therefore the pinion 56 and the rack 64 lock up and are damaged. Moreover, because the piston 62 cannot move below its initial position, there is a possibility of the operation of the force limiter being affected. A pretensioner according to the preamble of claim 1 is disclosed in US-A-4 508 287. This pretensioner comprises a cylinder having a closed and an opposite open end with a piston movable in the cylinder upon ignition of a propellant charge. Upon ignition of the propellant charge the piston with an attached weight is accelerated in the cylinder tube and thereby is leaving the top edge of the cylinder. A rope which is coupled with the piston is rotating the winding shaft and thereby retracting the webbing. A pretensioner being similar to that of above mentioned figure 5 is disclosed in US-A-5 794 876. This known pretensioner comprises a rack meshing with a pinion. The rack comprises a gas generator case which can drive the rack via a piston in a direction to retract the webbing. The rack comprising a cushioning member at the site of the piston is driven with its free end into a recessed guide portion of the guiding cylinder. US-A-4 006 644 discloses a safety belt tensioning apparatus having a piston to be displaced in the direction of a winding roller by initiating a gas pressure. The other end of this piston rod is provided with a soft metal sheathing which can engage axial helical grooves on the inside surface of the winding roller in order to retract the webbing. SUMMARY OF THE INVENTION In consideration of the above, an object of the present invention is to provide a pretensioner for a webbing retractor which can prevent noise being generated by the bottom of the cylinder coming into contact with the piston due to vibration and the like, at the same time as enabling costs to be reduced. For solving this object of the present invention the above mentioned pretensioner for a webbing retractor is provided with the features according to claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view showing the schematic structure of the webbing retractor of an embodiment of the present invention. Fig. 2 is an exploded perspective view showing the schematic structure of a webbing retractor. Fig. 3 is a side view showing the operation of a pretensioner for a webbing retractor. Fig. 4 is a side view showing the operation of a force limiter for a webbing retractor. Fig. 5 is a side view showing the schematic construction of a conventional webbing retractor. Fig. 6 is a side view showing the schematic construction of a conventional webbing retractor. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 shows a side view of the schematic construction of a webbing retractor 38 constructed using the pretensioner 10 for a webbing retractor of an embodiment of the present invention. Fig. 2 shows an exploded perspective view of the schematic construction of the webbing retractor 38. The webbing retractor38 is provided with a frame 12 which is fixed to a vehicle. A winding shaft 14 is fixed to the frame 12 so as to be rotatable therewithin and a webbing 16 is wound onto the winding shaft 14. The webbing retractor 38 is further provided with a rack and pinion type of pretensioner 10 and the pinion 18 is connected to one end of the winding shaft 14. The pinion 18 is disposed so as to always rotate integrally with the winding shaft 14 and, therefore, the winding shaft 14 is rotated by the rotation of the pinion 18 resulting in the webbing 16 being either wound onto or unwound from the winding shaft 14. A cylinder 20 is fixed to the frame 12. The cylinder 20 is formed in a hollow cylindrical shape with the distal end 22 of the cylinder 20 open in the vicinity of the pinion 18. In contrast, a cylindrical concave portion 26 is provided in the bottom portion 24 of the cylinder 20. This concave portion 26 is made with a smaller diameter than the internal diameter of the cylinder 20 so that the bottom portion 24 of the cylinder 20 and the concave portion 26 form a step which is used for positioning an O ring 34, which is described below, and holding the O ring 34 in position. Moreover, an unillustrated gas supply aperture is provided in the concave portion 26 from which a gas serving as a fluid is supplied into the cylinder 20 when a vehicle executes an emergency deceleration due to a collision or the like. A substantially disc-shaped piston 28 is provided so as to be able to move inside the cylinder 20. Accordingly, when gas is supplied to the inside of the cylinder 20, the gas pressure causes the piston 28 to move in the direction of the arrow C in Fig. 3. A rack 30 is provided integrally with the surface of the piston 28 nearest the pinion 18. The rack 30 matches the pinion 18 and when the rack 30 is moved together with the piston 28 in the direction of the arrow C in Fig. 3, the rack 30 meshes with the pinion 18 and causes the pinion 18 to rotate in the direction in which the webbing 16 is retracted (the direction of the arrow A in Fig. 3). A cylindrically-shaped seal holding portion 32 is formed integrally with the surface of the piston 28 nearest the bottom portion 24 of the cylinder 20. An O ring 34 is fitted onto the external periphery of the seal holding portion 32 as a sealing member. The O ring 34 has elastic properties and seals the gap between the piston 28 and the internal wall 36 of the cylinder 20. The O ring 34 abuts the bottom portion 24 of the cylinder 20 so as not to allow the piston 28 to come into direct contact with the bottom portion 24 of the cylinder 20. The position of the piston 28 in this state is the initial position of the piston 28. In this normal state where the O ring 34 abuts the bottom portion 24 of the cylinder 20, the seal holding portion 32 is positioned inside the aforementioned concave portion 26 of the bottom portion 24 of the cylinder 20. Moreover, the concave portion 26 is formed with sufficient depth that, when the O ring 34 is in an elastically deformed state, the seal holding portion 32 does not come into contact with the bottom wall 27 of the concave portion 26. The above-described type of webbing retractor 38 provided with. the pretensioner 10 using a rack and pinion is further provided with an unillustrated force limiter mechanism. When the force limiter is operated, the pinion 18 rotates in the opposite direction to the direction in which the webbing 16 is retracted (the direction shown by the arrow B in Fig. 4) thereby unwinding the webbing 16. Accordingly, when the vehicle executes an emergency deceleration, the load on the vehicle occupant does not exceed a predetermined value. The operation of the present embodiment will now be explained. During the assembly process for the pretensioner 10 of the webbing retractor38 having the above-described structure, an O ring 34 is fitted onto the external periphery of a seal holding portion 32 formed integrally with the surface of the piston 28 nearest the bottom portion 24 of the cylinder 20. The piston 28 is inserted into the cylinder 20 together with the O ring 34. Therefore, the conventional cutting process for forming a seal holding groove is unnecessary, allowing costs to be reduced. In addition, the task of fitting the O ring in the seal holding groove by stretching the O ring is unnecessary, simplifying the assembly process. When the vehicle is being driven normally, the piston 28 does not directly come into contact with the bottom portion 24 of the piston 20 as in a conventional apparatus, but instead the O ring 34 abuts the bottom portion 24 of the cylinder 20, thereby preventing noise of the contact between the bottom portion 24 of the cylinder 20 and the piston 28 being generated by vibration and the like. When the vehicle executes an emergency deceleration, then, as is shown in Fig. 3, gas is supplied to the cylinder 20 and the piston 28 is moved in the direction shown by the arrow C in Fig. 3 by the pressure of the gas. When the piston 28 is moved in the direction of the arrow C in Fig. 3, the rack 30 moves together with the piston 28 and meshes with the pinion 18, rotating the pinion 18 in the direction in which the webbing 16 is retracted (the direction shown by the arrow A in Fig. 3). When the pinion 18 is rotated in the direction in which the webbing 16 is retracted, the webbing is wound onto the winding shaft14, thereby removing the slackness in the webbing 16. At this point, when the piston 28 is moved by the pressure of the gas, the pressure of the gas acts on the O ring 34. The O ring 34 is unable to move from the seal holding portion 32 because it is held in place by the piston 28. Therefore, the O ring 34 seals the gap between the piston 28 and the inner wall 36 of the cylinder 20 thus increasing the air-tightness between the piston 28 and the cylinder 20. When the force limiter is operated, then, as is shown in Fig. 4, the pinion 18 is rotated in the opposite direction to the direction in which the webbing 16 is retracted (the direction shown by the arrow B in Fig. 4), thereby unwinding the webbing 16. Accordingly, the load on a vehicle occupant in an emergency deceleration is prevented from rising above a predetermined value. At this point, because the pinion 18 is rotated in the opposite direction to the direction in which the webbing 16 is retracted, then even if the piston 28 moves in the direction of the bottom portion 24 of the cylinder 20 (the direction shown by the arrow D in Fig. 4), the O ring 34 abuts the bottom portion 24 of the cylinder 20 preventing the piston 28 from making direct contact with the bottom portion 24 of the cylinder 20. Accordingly, no noise is generated by the bottom portion 24 of the cylinder 20 contacting the piston 28. Further, when the O ring 34 abuts the bottom portion 24 of the cylinder 20, due to its elastic properties, the O ring 34 is slightly squashed. At this point, with the O ring 34 thus elastically deformed, the seal holding portion 32 does not come into contact with the bottom wall 27 of the concave portion 26 of the bottom portion 24 of the cylinder 20. Accordingly, the pinion 18 and the rack 30 can be prevented from locking up and being damaged. Moreover, because the piston 28 is able to move below its initial position, it can be prevented from having any effect on the operation of the force limiter. Further to this still, because the piston of the present embodiment is not structured with a separate piston body and pressure receiving plate as in the conventional apparatus, the number of parts is reduced, thereby allowing costs to be reduced. As described above, in the webbing retractor 38 of the present embodiment, costs are able to be reduced and the generation of noise from contact between the bottom portion 24 of the cylinder 20 and the piston 28 caused by vibration and the like can be prevented.

Claims: A pretensioner (10) for a webbing retractor (38) comprising: a winding shaft (14) onto which a webbing (16) wound; a cylinder (20) into which a fluid is supplied when a vehicle makes a sudden deceleration; a piston (28) which is disposed so as to be able to move inside said cylinder (20), and which is moved inside said cylinder (20) by the pressure of said fluid so as to rotate said winding shaft (14) in the direction in which said webbing (16) is retracted; and a sealing member (34) which has elastic properties, which seals the gap between the internal wall of said cylinder (20) and said piston (28), and which abuts a bottom portion (24) of said cylinder (20) so as to prevent said piston (28) and said bottom portion (24) of said cylinder (20) from coming into contact, characterized in that a seal holding portion (32) is formed integrally with the surface of said piston (28) nearest the bottom portion (24) of said cylinder (20) and protrudes in the shape of a cylinder, that the sealing member (34) is fitted onto the external periphery of said seal holding portion (32) and that a concave portion (26) corresponding to said seal holding portion (32) is provided in said portion (24) of said cylinder (20) and said concave portion (26) is formed with sufficient depth that, when said sealing member (34) is in an elastically deformed state, said seal holding portion (32) does not come into contact with the bottom wall (27) of said concave portion (26). The pretensioner for a webbing retractor according to claim 1, wherein to one end of the winding shaft (14) a pinion (18) is connected, which always rotates integrally with said winding shaft (14), and that the piston (28) is provided integrally with a rack (30) which meshes with said pinion (18) and causes said pinion (18) to rotate. The pretensioner for a webbing retractor according to claim 1 or 2, wherein said fluid is a gas. A pretensioner for webbing retractor according to claim 2 or 3, wherein the rack (30) is provided integrally with said piston (28). The pretensioner for a webbing retractor according to any of claims 1 through 4, wherein said sealing member is an O ring (34). The pretensioner for a webbing retractor according to any of claims 1 through 5, wherein a force limiter mechanism is provided to prevent the load on an occupant of a vehicle from rising above a predetermined value when said vehicle executes an emergency deceleration.

Inventors: HORI SEIJI, NAGATA TOMONORI, NISHIDE SEIJI, HORI, SEIJI, NAGATA,TOMONORI, NISHIDE, SEIJI, Hori, Seiji c/oK.K.TOKAI-RIKA-DENKO-SEISAKUSHO, Nagata,Tomonori c/oK.K.TOKAI-RIKA-DENKO-SEISAKUSHO, Nishide, Seiji c/oK.K.TOKAI-RIKA-DENKO-SEISAKUSHO
Applicants: TOKAI RIKA CO LTD, KABUSHIKI KAISHA TOKAI-RIKA-DENKI-SEISAKUSHO
Application year: 1999
Main classification: B60R22
IPC codes: B60R22