Webbing retractor with a gear mechanism

Abstract: A gear mechanism for reducing a rotational speed of a driving gear (10) and transferring the reduced rotational speed to a gear (17) to be driven comprises an arbitrary number of gear teeth (11,12) attached to the driving gear and smaller than the number of teeth determined by a module and a stopper (13) having a stopper surface (14) which is attached to the driving gear (10) so as to be displaced relative to said gear teeth along the axial direction of the driving gear and which draws a circle identical in size to a circle drawn by a locus of rotation of an addendum of each gear tooth upon rotation of the driving gear and meshes with gear teeth (19) of the driven gear (17) upon disengagement of the gear teeth (11,12) from the teeth (18,19) of the driven gear so that the rotation of the driven gear is controlled by the stopper. Thus, when the gear teeth (11,12) are in disengagement with the teeth (18,19) of the driven gear, the stopper (13) is maintained in meshing engagement with the gear teeth (19) of the driven gear (17) so as to prevent the driven gear from rotating. This gear mechanism can be used for reducing the rotational speed of a webbing retractor and transferring the reduced rotational speed to a driven gear for opening and closing a contact in relation to an extended length of webbing.

Description: The present invention relates to a webbing retractor according to the pre-characterizing part of claim 1. A seat belt system attached to a vehicle is constructed as shown in Fig. 3. In the seat belt system, a webbing 51 is manufactured as an elongated integral-type member. One end of the webbing 51 is wound on a webbing take-up spindle of a retractor 53 attached to a lower portion of a vehicle body so as to correspond to a seat 50 by an urging force. The webbing 51 is pulled out of the retractor 53 and passes through a shoulder anchor 55 attached to an upper portion in the vehicle's interior. Thereafter, the other end of the webbing 51 is fastened to an anchor plate provided adjacent to the retractor 53 attached to the lower portion of the vehicle body. Further, the webbing 51 has a tongue plate 52 held so as to be movable along the longitudinal direction of the webbing 51. On the other hand, a buckle 54 is attached to the vehicle body. When the tongue plate 52 engages in the buckle 54, an occupant seated on his/her seat 50 puts on the webbing 51. In the state in which the occupant has put on the webbing, a portion of the webbing 51 from a shoulder anchor 55 thereof to the tongue plate 52 serves as a shoulder webbing 51A, whereas a portion thereof from the tongue plate 52 to the anchor plate serves as a lap webbing 51B. When the vehicle suddenly decelerates, the retractor 53 is activated so as to stop the withdrawal of the webbing 51. A certain type of retractor 53 detects an extended length of the webbing 51 so as to perform various operations such as the detection of the presence or absence of the fastening of the seat belt to the occupant, the switching of a lock mechanism, the release of a safety device for a pretensioner, etc. This extended webbing length is detected by, for example, reducing a rotational speed of a webbing retractor and transferring the reduced rotational speed to a driven gear and opening and closing an opening/closing contact by a part of the driven gear. In the conventional reduction gear mechanism, however, the minimum number of teeth of the pinion was limited from the viewpoint of the strength of the teeth thereof to obtain a large reduction ratio under a size-reduced gear mechanism and a double-reduction gear was necessary. In accordance with the pre-characterizing part of claim 1, US-A-38 53 284 discloses a webbing retractor in which the stopper provided integrally with the driving gear is constituted by the circumferential surface of the driving gear cooperating with a correspondingly curved portion provided on the driven gear as the second gear teeth thereof. The driving gear is provided with a cutout axially adjacent the first gear tooth so that when the first gear tooth of the driving gear engages the driving gear so as to rotate the driven gear, said cutout allows that the stopper of the driving gear comes into engagement with a further curved portion of the driven gear. US-A-28 81 630 discloses a mechanical counter having a driven gear and a driving gear having a similar stopper configuration as the above discussed US'284. With the foregoing in view, it is therefore an object of the present invention to provide a webbing retractor having the features of the pre-characterizing part of claim 1 and being provided with a gear mechanism capable of enhancing a reduction ratio thereof and decreasing the number of parts so as to reduce the size thereof. This object is achieved by the features of the characterizing part of claim 1. Preferred embodiment are defined in the dependent patent claims. When a webbing attached to a seat belt system is pulled out and wound up, the webbing take-up spindle of the webbing retractor is rotated to turn the driving gear. Since the number of the teeth of the driving gear is smaller than the number of the teeth determined by the normal module, the driven gear is rotated under a further reduced rotational speed as compared with the normal gear mechanism. Namely, the number of rotations of the driven gear per rotation of the driving gear is reduced. Further, the driving gear has the stopper. When the first gear teeth are in disengagement with the second gear teeth, the stopper is maintained in meshing engagement with the second gear teeth so as to prevent the driven gear from rotating. Thus, the mesh of the first gear teeth with the second gear teeth and the engagement of the stopper with the second gear teeth are alternately repeated under the rotation of the driving gear so that the driven gear is intermittently rotated, thereby making it possible to enhance a reduction ratio. Namely, when the first gear tooth of the driving gear meshes with the second gear tooth of the driven gear, a stopper surface is disengaged from the second gear teeth to transfer the rotation of the driving gear to the driven gear, whereby the driven gear is driven. When the stopper of the driving gear is in meshing engagement with the second gear teeth of the driven gear, the driven gear is prevented from rotating so as to stop rotating. Thus, the reduction ratio can be enhanced by intermittently rotating the driven gear. Further, the present webbing retractor includes the switch device for generating an on/off signal according to the rotation of the driven gear. The on/off signal is sent to an angular displacement detector where an angular displacement of the driven gear is detected. A webbing wear detector can detect, based on the detected angle of rotation, whether the webbing has been fastened to the occupant, for example. According to the present invention as described above, since the stopper surface is separated from between the teeth of the driven gear when the gear tooth of the driving gear meshes with the driven gear, the rotation of the driving gear is transferred to the driven gear so that the driven gear is driven. When the stopper surface of the driving gear meshes between the teeth of the driven gear, the driven gear is prevented from rotation so as to stop rotating. Therefore, the reduction ratio can be enhanced by intermittently rotating the driven gear. Thus, according to the present invention, the reduction ratio of the gear mechanism can be enhanced and the number of parts can be reduced as compared with the conventional gear mechanism, thereby making it possible to reduce the gear mechanism in size. The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to the accompanying drawings wherein: Fig. 1 is a perspective view showing a gear mechanism according to an embodiment of the present invention; Fig. 2A is a perspective view illustrating a meshed state of the gear mechanism shown in Fig. 1; Fig. 2B is a perspective view depicting another meshed state of the gear mechanism shown in Fig. 1; Fig. 3 in a schematic perspective view showing a vehicle belt system; Fig. 4 is a front view illustrating a gear mechanism applied to a retractor to facilitate the understanding of the present invention; Fig. 5 is a cross-sectional view taken along line IX - IX of Fig. 4; and Fig. 6 is an exploded perspective view depicting the retractor shown in Fig. 4. DETAILED DESCRIPTION THE PREFERRED EMBODIMENTS An embodiment of the present invention will hereinafter be described with reference to the accompanying drawings. Figs. 1, 2A and 2B show an embodiment of the present invention. The present embodiment is one of a type wherein two teeth of a gear to be driven are continuously rotated relative to one rotation of a pinion so that the driven gear is intermitted once (i.e., the driven gear is rotated once per rotation of the pinion and caused to cease once). Fig. 1 is a perspective view showing a principal part of a gear mechanism. Figs. 2A and 2B are respectively views showing meshed states of gears. Fig. 1 shows a state in which the rotation of a gear 17 to be driven is controlled by a stopper 13 of a pinion 10. Assuming that the number of teeth determined by a module, i.e., an arbitrary number smaller than a value obtained by dividing the diameter of a pitch circle by the module, e.g., the number of teeth corresponding to the value obtained by dividing the diameter of the pitch circle by the module is regarded as five, the number of gear teeth of the pinion 10 that is a driving gear, is set to two teeth smaller than five teeth. For example, three teeth are removed from the five teeth and the remaining adjacent two teeth are formed as continuous gear teeth 11 and 12. The pinion 10 has the stopper 13 coaxially and integrally with the gear teeth 11 and 12. The gear teeth 11 and 12 respectively include tooth surfaces 11A and 12A having widths equal to half the thicknesses of the gear teeth 11 and 12 and tooth surfaces 11B and 12B having widths the same as those of the gear teeth 11 and 12. The stopper 13 is shaped in the form of a partly-cut disc and includes a stopper surface 14 which draws a circular arc or circle identical to that drawn by the locus of rotation of a tip or addendum of each of the gear teeth 11 and 12. Namely, the stopper 14 is formed on the back sides (i.e., the reverse side of Fig. 1) of the gear teeth 11 and 12 so as to be displaced in the form of steplike offsets relative to the tooth surfaces llA and 12A, i.e., in the axial direction of the pinion 10. Further, when the stopper surface 14 is interposed between gear teeth 19 and 19 of the driven gear 17 to be described later, the stopper 13 serves so as to prevent the driven gear 17 from rotating. A plurality of teeth 18 each having two tooth surfaces identical to the tooth surfaces 11A and 12A of the gear teeth 11 and 12 of the pinion 10 and a plurality of teeth 19 each having two tooth surfaces identical to tooth widths of the tooth surfaces 11B and 12B are alternately attached to the driven gear 17. Namely, the teeth 18 of the driven gear 17 are disposed on the upper side (this side of Fig. 1) and maintained in meshing engagement with the tooth surfaces 11A and 12A of the gear teeth 11 and 12 of the pinion 10. Further, the stopper surface 14 enters into the back side of tooth surfaces of each tooth 18 of the driven gear 17. When the stopper surface L4 of the pinion 10 is maintained in meshing engagement with or corresponds to the teeth 19 and 19 of the driven gear 17, the back of the tooth 18 of the driven gear 17 is opposed to the surface (i.e., the surface on this side of Fig. 1) of the stopper 13. Although not shown in the drawing, the pinion 10 and the driven gear 17 are supported by their corresponding support shafts. The pinion 10 is rotated by an unillustrated drive source. The operation of the present invention will now be described. The pinion 10 is rotated in a counterclockwise direction from the state shown in Fig. 1 if necessary, so that the stopper 13 is withdrawn from between the teeth 19 and 19 of the driven gear 17. Further, the tooth surface llA of the gear tooth 11 is maintained in meshing engagement with its corresponding tooth surface 18A of one tooth 18 of the driven gear 17 as shown in Fig. 2A so that the tooth 18 of the driven gear 17 is rotated in a clockwise direction. Namely, the driven gear 17 is rotated by one tooth. Further, when the pinion 10 is rotated, the tooth surface 12B of the gear tooth 12 is maintained in meshing engagement with its corresponding tooth surface 19A of one tooth 19 of the driven gear 17 as shown in Fig. 2B so that the driven gear 17 is further rotated by one tooth. When the gear teeth 11 and 12 are released from meshing with the driven gear 17, the stopper surface 14 of the stopper 13 meshes with the tooth surfaces 19A and 19B of the teeth 19 and 19 of the driven gear 17 so as to control the rotation of the driven gear 17 as shown in Fig. 1. Namely, when the stopper 13 is in meshing engagement with the driven gear 17, the driven gear 17 cannot be freely rotated. Since the driven gear 17 is rotated by two teeth so as to perform one intermittent operation when the pinion 10 is rotated once, a reduction ratio can be enhanced. Further, since the gear teeth 11 and 12 are formed integrally with the stopper 13 in consideration of the strength of the gear teeth 11 and 12 of the pinion 10, no problem occurs in the strength of the gear teeth 11 and 12 even if the number of teeth is smaller than the value obtained by dividing the diameter of the pitch circle of the pinion 10 by the module. Thus, the reduction ratio of the gear mechanism can be enhanced and the number of parts can be reduced as compared with the conventional gear mechanism, thereby making it possible to reduce the gear mechanism in size. As an alternative embodiment although not shown in the drawing, may be mentioned a gear mechanism wherein the number of gear teeth of the pinion 10 is set to three teeth provided continuously and the tooth 18 of the driven gear 17 Is continuously provided two, followed by provision of one tooth 19, i.e., when two teeth 18 and one tooth 19 are repeatedly arranged, the driven gear 17 is rotated by three teeth with respect to one rotation of the pinion 10 so that one intermittent operation is performed. Figs. 4 through 6 illustrate an embodiment to facilitate the understanding of the present invention. The present embodiment is one of a type wherein the gear mechanism according to Figs. 1 and 2 is applied to a retractor 53 which is a webbing retractor. Further, the webbing retractor includes a switch mechanism or device in relation to the gear mechanism. Accordingly, the construction and operation of the gear mechanism will be described with reference to Figs. 1 and 2. Fig. 4 is a front view showing the retractor according to the present embodiment. Fig. 5 is a cross-sectional view taken along line IX - IX of Fig. 4. Fig. 6 is an exploded perspective view showing an essential part of the retractor. As shown in Figs. 5 and 6, a pinion 10, which serves as a driving gear, is fixed to a leading end of a webbing take-up spindle 40 and rotated integrally with the webbing take-up spindle 40. Further, two continuous gear teeth 11 and 12 and a stopper 13 are integrally formed so as to constitute the pinion 10 as shown in Fig. 1. The gear teeth 11 and 12 respectively have tooth surfaces 11A and 12A. In which the thicknesses of the teeth are reduced and tooth surfaces 11B and 12B in which the thicknesses of the teeth are increased. The stopper 13 has a stopper surface 14 which draws a circle identical to that drawn by the locus of rotation of an addendum of each of the gear teeth 11 and 12. Namely, the stopper surface 14 is shaped on the back sides of the gear teeth 11 and 12 in the form of a steplike offset. The stopper 13 controls the rotation of the driven gear 17 with the stopper surface 14 interposed between gear teeth 19 and 19 of the driven gear 17 to be described later. A storage portion 44 is formed in a cover 43. Further, a hole 43a for allowing the pinion 10 to project into the storage portion 44 and a shaft 43b are formed in the storage portion 44. As shown in Figs. 4 through 6, the driven gear 17 is supported by the shaft 43b. Teeth 18 each having two tooth surfaces equal to the tooth surfaces 11A and 12A of the gear teeth 11 and 12 of the pinion 10 and teeth 19 each having two tooth surfaces equivalent to thicknesses of the teeth 11 and 12 having the tooth surfaces 11B and 12B are alternately attached to the driven gear 17. Namely, the teeth 18 of the driven gear 17 are disposed on the upper side of the driven gear 17 and maintained in meshing engagement with the tooth surfaces 11A and 12A of the gear teeth 11 and 12 of the pinion 10. Further, the stopper surface 14 meshes with the lower side of the tooth surface of each tooth 19 of the driven gear 17. When the stopper 13 of the pinion 10 is in engagement with the teeth 19 and 19 of th driven gear 17, one surface of the tooth 18 of the driven gear 17 is opposed to one surface of the stopper 13. A switch device 49 comprises a first contact member 47 fixed to the driven gear 17 and a second contact member 51 (not shown) fixed to a switch cover 48. When the gear 17 is rotated through a predetermined angle in a predetermined direction, the first contact member 47 is brought into contact with the second contact member 51 so that the switch device 49 is turned on. On the other hand, when the gear 17 is rotated in the direction opposed to the predetermined direction, the first contact member 47 is separated from the second contact member 51 so that the switch device 49 is turned off. Thus, the webbing take-up spindle 40 is rotated so as to turn the driven gear 17 through a predetermined angle in a predetermined direction, the first contact member 47 is brought into contact with the second contact member 51 provided within the switch cover 48. Owing to the contact referred to above, an on signal is generated from the switch device 49 so as to be sent to a turning angle detector 55 where an angular displacement of the driven gear 17 is detected. Incidentally, the switch cover 48 is fixed to the cover 43 so as to cover the storage portion 44 of the cover 43, i.e., the gear mechanism. In the above-described construction, when a shoulder webbing 51A (see Fig. 3) is taken up or pull out according to the fastening of the webbing to a vehicle occupant, the release of the occupant from its fastening or a change in occupant's position at the time that the webbing has been fastened to the occupant, the webbing take-up spindle 40 is rotated. When the shoulder webbing 51A is wound on the webbing take-up spindle 40, for example, the webbing take-up spindle 40 is rotated in the counterclockwise direction. In doing so, the tooth surface 11A of the gear tooth 11 is maintained in meshing engagement with its corresponding tooth surface 18A of the tooth 18 of the driven gear 17 as shown in Fig. 2A so that the corresponding tooth 18 of the driven gear 17 is rotated in the clockwise direction. Namely, the driven gear 17 is rotated by one tooth. Further, when the pinion 10 is rotated, the tooth surface 12B of the gear tooth 12 is maintained in meshing engagement with its corresponding tooth surface 19A of the tooth 19 of the driven gear 17 as shown in Fig. 2B so that the driven gear 17 is further rotated by one tooth. When the gear teeth 11 and 12 are released from meshing engagement with the driven gear 17, the stopper surface 14 of the stopper 13 is maintained in meshing engagement with the tooth surfaces 19A and 19B of the teeth 19 and 19 of the driven gear 17 to control the rotation of the driven gear 17 as shown in Fig. 1. Namely, when the stopper 13 is in engagement with the driven gear 17, the driven gear 17 cannot be freely rotated. When the pinion 10 is rotated, the contact 47 is rotated integrally with the driven gear 17 and brought into contact with the unillustrated contact of the switch cover 48. As a result, the length of extension of the shoulder webbing 51A from the retractor 53 is detected to activate a seat belt wear warning device, a lock-means switching device or the like. In the present embodiment, since the driven gear 17 is rotated by two teeth so as to perform one intermittent operation when the pinion 10 is rotated once, a reduction ratio can be enhanced. Further, since the gear teeth 11 and 12 are formed integrally with the stopper 13 in consideration of the strength of the gear teeth 11 and 12 of the pinion 10, no problem occurs in the strength of the gear teeth 11 and 12 even if the number of teeth is smaller than a value obtained by dividing the diameter of a pitch circle of the pinion 10 by a module. Thus, the present embodiment can be applied to a webbing device or retractor capable of enhancing a reduction ratio of a gear mechanism. Further, since the present embodiment may use a single-reduction gear alone as compared with the conventional example in which a double-reduction gear is used to enhance the reduction ratio, the number of parts can be reduced and hence the webbing device equipped with the gear mechanism can be reduced in size. The number of teeth of the driving gear (pinion) is not necessarily limited to those employed in the present embodiment. If the number of teeth is the number of teeth smaller than the number of teeth determined by the module of the driving gear, then the corresponding number of teeth can be applied in the same manner as described above. Even if a gear mechanism applied to a retractor such as a webbing retractor is used as, for example, a Geneva gear or the like of a type wherein when an engagement portion of a pinion engages a driven gear under the continuous rotation of the pinion, the driven gear is rotated and the engagement portion restrains a deactivated state of the driven gear in a state of being in disengagement with the driven gear, whereby the driven gear is intermittently rotated, the present invention can be applied to the webbing retractor.

Claims: A webbing retractor for winding a webbing fastened to a vehicle occupant on a webbing take-up spindle provided therein, comprising: a driving gear (10) having at least one first gear tooth, said driving gear being rotated under the action of rotation of said webbing take-up spindle; a driven gear (17) having a plurality of second gear teeth (18,19) each maintained in meshing engagement with said driving gear, said driven gear being intermittently rotated under the action of rotation of said driving gear in a state in which said first gear tooth is in meshing engagement with a second gear tooth; a stopper (13) is provided integrally with said driving gear, said stopper being meshed with second gear teeth so as to stop the rotation of said driven gear upon disengagement of said first gear tooth from second gear teeth, wherein when the first gear tooth of said driving gear is disengaged from the second gear tooth of said driven gear a stopper surface (14) is placed between second gear teeth so as to control rotation of said driven gear; wherein said stopper is a partly-cut and substantially disc-like portion having an arcuate outer peripheral surface as said stopper surface, characterised in that the driving gear has an arbitrary number of first gear teeth, and said second gear teeth of said driven gear comprise a first plurality of gear teeth (18) each having a thickness substantially the same as an axially-extending thickness of said driving gear and a second plurality of gear teeth (19) each having a thickness substantially the same as the thickness of said each tooth of said driving gear, said first plurality of gear teeth and said second plurality of gear teeth being respectively alternately attached to said driven gear. A webbing retractor according to claim 1, wherein said arbitrary number of first gear teeth are adjacent two gear teeth (11, 12) of the number of teeth determined by the module. A webbing retractor according to claim 1, comprising a switch device (49) turned on and off in response to the rotation of said driven gear (17). A webbing retractor according to claim 3, wherein said switch device includes a first contact rotated together with said driven gear and a second contact attached to a cover for covering said driven gear. A webbing retractor according to claim 3, wherein said stopper surface (14) is displaced relative to said first gear teeth (11, 12) along the axial direction of said driving gear (10) and draws a circle identical in size to a circle drawn by a locus of rotation of an addendum of said each first gear tooth (11, 12) upon rotation of said driving gear (10), said stopper (13) preventing said driven gear (17) from rotation by meshing said stopper surface (14) with said second gear teeth (19) upon disengagement of said first gear teeth (11, 12) from said second gear teeth (19).

Inventors: SEIJI HORI, SEIJI, HORI, SEIJI, HORI, C/O K.K. TOKAI-RIKA-DENKI-SEISAKUSHO
Applicants: TOKAI RIKA CO LTD, KABUSHIKI KAISHA TOKAI-RIKA-DENKI-SEISAKUSHO
Application year: 1996
Main classification: F16H27
IPC codes: B60R22, F16H27