GB2262701A

GB2262701A - Seat belt retractor with pretensioner

Info

Publication number: GB2262701A
Application number: GB9226956A
Authority: GB
Inventors: Osamu Tokugawa; Haruyuki Ikesue
Original assignee: NSK Ltd
Current assignee: NSK Ltd
Priority date: 1991-12-26
Filing date: 1992-12-24
Publication date: 1993-06-30
Also published as: JPH0556690U; GB9226956D0; DE4242784A1

Description

2262701 1 - SEAT BELT RETRACTOR WITH PRETENSIONER

FIELD OF THE INVENTION a) Field of the Invention

The present invention relates to a seat belt retractor having a pretensioner so that slack of a webbing can be eliminated in the event of an emergency by winding up the webbing on a take-up spindle of a retractor. b) Description of the Related Art

With respect to a seat belt system for protecting an occupant in safe in a seat of a vehicle, it has heretofore been tended to lower the webbingwinding force of its retractor with a view toward making the occupant feel less that he is wearing a webbing. This however inevitably results in greater play or slack of the webbing, leading to the potential danger that in the event of an emergency such as collision of the vehicle, restraint of the occupant is delayed to result in failure in effectively restraining him.

With a view toward eliminating such play or slack of the webbing by winding in the webbing in the event of an emergency, there have been proposed seat belt systems which are each equipped with a pretensioner assembled therein to instantaneously rotate a take-up spindle of its retractor in a winding direction.

The pretensioner comprises, for example, a cable wound around a pulley mounted on the take-up spindle of the retractor and a piston connected with one end of the cable and received slidably within a cylinder. By thrust or drive force produced based on the pressure of an expanding gas applied to the piston, pulling force is applied to the cable so that the cable causes the take-up spindle of the retractor to rotate in a webbingwinding direction. This makes it possible to wind in a webbing, said webbing being applied to an occupant, in the event of an emergency.

In such a pretensioner, the cable is normally kept out of engagement with the pulley and, in normal use, the cable does not interfere with rotation of the take-up spindle and is wound around the pulley, said pulley being integral with the take-up spindle, upon actuation of the pretensioner. Accordingly, force is transmitted from the cable to the pulley based on frictional force which is developed between the cable and the pulley.

However, such transmission of force through frictional force as described above is unavoidably accompanied by occurrence of slip between the cable and the pulley. As a result, tightening of the webbing z 4 wound on the take-up spindle cannot be conducted surely and moreover, the tightening cannot be effected to a predetermined constant degree. The tightening of the wound webbing may therefore become too little or too much depending on the amount of slip. If the frictional engagement between the cable and the pulley is set at an excessively tight level, it makes it difficult to have the cable released from the pulley immediately after completion of the winding-in drive of the take-up spindle by the cable so that the take-up spindle cannot be rotated in the webbing- releasing direction. This prevents winding-out of the webbing, leading to the potential danger that the webbing may remain restraining the occupant in the seat and hence may not permit his emergency escape.

Seat belt systems equipped with a pretensioner have therefore been proposed as disclosed, for example, in Japanese Utility Model Application Laid-open (Kokai) No. HEI 1-161156 and Japanese Patent Application LaidOpen (Kokai) No. HEI 1-168547.

In such a pretensioner-equipped retractor as disclosed, for example, in the above Japanese publications, segments which have been formed by dividing an annular body into a plurality of arcuate pieces are disposed around a gear mounted on a take-up spindle of the retractor so that the segments surround the gear with a radial interval left therebetween to such an extent that the segments and the gear are kept out of contact. Both or either one of a casing and a cover is provided with a like plural number of pins, which can be sheared off, in such a manner that the pins extend out from the casing and/or the cover and are maintained in engagement with their corresponding segments. A cable is wound on and about outer peripheral walls of the segments with said cable being connected at one end thereof with a piston of drive means.

When the drive means is actuated in the event of an emergency such as a vehicular collision and the cable is pulled, the segments with which the cable is always in frictional engagement shear off the pins and move inwardly in a radial direction, resulting in immediate engagement with the gear. Further pulling of the cable therefore causes the take-up spindle to rotate in a winding direction. This makes it possible to surely effect tightening of a wound webbing without development of idling or slip on the cable and the segments.

The above Japanese publications also disclose a retractor equipped with a pretensioner. Segments which have been formed by dividing an annular body into a t plurality of arcuate pieces are connected together with resilient members interposed therebetween so that the segments are biased radially and outwardly. These segments are arranged around a gear mounted on a take-up spindle of the retractor in such a manner that the segments surround the gear and can be selectively brought into contact with or separated from the gear. A cable is wound on and about outer peripheral walls of the segments with said cable being connected at one end thereof with a piston of drive means.

When the drive means is actuated in the event of an emergency such as a vehicular collision and the cable is pulled, the segments with which the cable is always in frictional engagement are caused to move radially and inwardly, resulting in immediate engagement with the gear to cause the take-up spindle to rotate in a webbing winding direction. This makes it possible to surely effect tightening of a wound webbing without development of idling or slip on the cable and the segments. After the radial and inward movement and subsequent rotation of the segments, the segments are allowed to move back radially and outwardly from the gear under the force of the resilient members. Accordingly, the take-up spindle can now rotate freely as before the emergency, thereby facilitating emergency es- cape from the vehicle.

However a pretensioner of such a construction as described above is accompanied by the problems that, because the segments are of the shape obtained by dividing an annular body into a plurality of arcuate pieces, the segments are complex in shape and difficult in machining and the pretensioner requires many parts and laborious assembly work.

Especially in the case of the former structure in which the plural shearable pins are provided on the cover or the like to hold their corresponding segments at positions where the segments are kept out of engagement with the gear, there is a high risk that shearing of the individual pins may not take place at once in the event of an emergency. In the case of the latter structure in which the resilient members applying radial and outward biasing force to the segments serve to hold the individual segments at positions where the segments are kept out of engagement with the gear, the individual segments are biased with the resilient members interposed therebetween so that radial and inward movements of the segments may not take place uniformly, resulting in the potential problem that the engagement of the segments with the gear may not be achieved completely.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to overcome the abovedescribed problem, and to provide a pretensioner-equipped seat belt retractor which is simple in construction, high in assembling efficiency and low in price and assures fail-free tightening of a webbing in the event of an emergency.

In one aspect of the present invention, there is thus provided a seat belt retractor having a pretensioner for bringing one end of a cable into engagement with a take-up spindle of the retractor in the event of a vehicular emergency whereby drive of the cable at an opposite end thereof causes the take-up spindle to rotate in such a direction as eliminating slack of a webbing, characterized in that said pretensioner comprises:

a plate fitted on an end portion of the take-up spindle and rotatable when rotary force of at least a predetermined magnitude is applied, a ratchet wheel secured on the end portion of the take-up spindle and rotatable together with the take-up spindle, a pawl pivotally supported on the plate and normally biased in such a direction that the pawl is kept out of engagement with the ratchet wheel, and a cable wound around the plate and connected at one end thereof with the pawl and at an opposite end thereof with drive means; whereby the cable driven at the opposite end thereof by drive means brings the pawl into engagement with the ratchet wheel, thereby causing the take-up spindle to rotate together with the plate.

In another aspect of the present invention, there is also provided a seat belt retractor having a pretensioner, characterized in that said retractor comprises:

a base, a take-up spindle rotatably supported on the base, webbing fastened to the take-up spindle, ratchet wheel secured on the take-up spindle, plate held on the base and movable relative to the base when force of at least a predetermined magnitude has been applied, a pawl supported on the plate, movable between an engagement position where the pawl is brought into engagement with the ratchet wheel and a non-engagement position where the pawl is kept out of engagement with the ratchet wheel, and biased toward the non-engagement position, and a cable connected at one end thereof with the pawl and at an opposite end thereof with drive means; whereby said drive means drives the cable in the event of a vehicular emergency so that the pawl is first moved from the non-engagement position to the engagement position and the take-up spindle is then rotated in a webbing-winding direction.

According to the above-described construction of the seat belt retractor in each of the aspects of this invention, the pawl is pivoted directly in the direction, where the pawl is rendered engageable with the ratchet wheel, by the drive force applied to the cable. Further, the rotary force of the plate rotated by the drive force is transmitted to the take-up spindle of the retractor through the engagement between the pawl and the ratchet wheel. It is therefore possible to effect tightening of the webbing without failure in the event of an emergency.

BRIEF DESCRIPTION OF THE DRAWINGS

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 10 is which:

FIG. 1 is a fragmentary front view of a pretensioner-equipped seat belt retractor according to one embodiment of the present invention; FIG. 2 is a cross-sectional view of the pretensioner, as viewed in the direction of arrows II-II in FIG. 1; FIG. 3 is a fragmentary, exploded, perspective view of the pretensioner shown in FIG. 1; and FIG. 4 is a fragmentary front view of the pretensioner of FIG. 1, depicting operation of the pretensioner.

DETAILED DESCRIPTION OF THE INVENTION

AND THE PREFERRED EMBODIMENT The pretensioner-equipped seat belt retractor shown in FIG. 1 through FIG. 3 is provided with a takeup reel 17 supported on a retractor base 3 and carrying a webbing 14 wound thereon in such a way that the webbing can be freely wound in or wound out. Like conventional retractors, the take-up reel 17 is normally biased by an unillustrated take-up spring, which is connected with a take-up spindle 2, in such a direction that the webbing 14 can be wound in. When the webbing 14 is about to be wound out at an acceleration of at least a predetermined value, rotation of the take-up spindle 2 is inhibited by an unillustrated emergency locking mechanism so that any further release of the webbing 14 is prevented.

The seat belt retractor also has a pretensioner 1 on one of side walls 3a of the retractor base 3 which is formed in a substantially square U-like configuration. The pretensioner 1 serves to rotate the take-up spindle 2 in such a direction that slack of the webbing 14 can be eliminated. The pretensioner 1 comprises a plate 4 defining therethrough a hole 4b as a center of rotation, through which hole 4b one end portion of the take-up spindle 2 extends in a fitted manner, a ratchet wheel 5 secured on the end portion of the take-up spindle 2 at a position outside the hole 4b, a pawl 6 pivotally supported on the plate 4, a wire 11 wound about the plate 4 and connected at one end thereof with the pawl 6, and drive means 16 connected with an opposite end of the wire 11. The pretensioner 1 is covered by an unillustrated housing.

The plate 4 is, as shown in FIG. 3, a substantially disk-shaped member centrally defining therethrough the hole 4b through which the one end portion of the take-up spindle 2 extends in the fitted manner. Formed on an outer peripheral edge portion of the plate 4 are a pair of flange portions 4d,4d extending in a radial direction and a pair of wire-winding portions 4c,4c formed substantially upright on one side of the plate 4. Further, the flange portions 4d,4d are provided with conical engaging beads 4a,4a at locations corresponding to paired holes 3b,3b, respectively. The engaging beads 4a,4a are normally maintained in engagement with their corresponding holes 3b,3b. In one of the flanges 4d, 4d, a pin receiving hole 4e is formed to pivotally support the pawl 6 thereon.

The plate 4 is rotatably held on the base side wall 3a by a bush 9 which is press-fitted and secured in a shaft through-hole 3c formed through the base side wall 3a. Under biasing force of a disk spring 10 interposed between the plate 4 and the bush 9, the plate 4 is pushed toward the base side wall 3a so that the holes 3b,3b lock the engaging beads 4a,4a in the direction of rotation of the plate 4. Therefore, the plate 4 is normally held while being prevented from rotation. When at least a predetermined magnitude of rotary force is applied to the plate 4, the conical engaging beads 4a,4a are unlocked from the holes 3b,3b against the biasing force of the disk spring 10 so that the plate 4 is rendered rotatable.

The ratchet wheel 5 is provided at a peripheral T.

13 - edge thereof with teeth 5a. The ratchet wheel 5 has been secured on the take-up spindle 2 by fitting the ratchet wheel 5 on an end portion of the take-up spindle 2 and then fixing the ratchet wheel 5 with a bolt 13 via a washer 12. The ratchet wheel 5 therefore rotates integrally with the take-up spindle 2.

The pawl 6 has a hook 6a engageable with the teeth 5a of the ratchet wheel 5, a through-hole 6b, and a connecting portion 6c with which the wire 11 is connected at one end thereof. Provided extending through the through-hole 6b is a pin a which has been secured on the plate 4 subsequent to its insertion in the pin receiving hole 4e of the plate 4. The pawl 6 is therefore pivotally supported in the neighborhood of an outer periphery of the ratchet wheel 5. Under biasing force of a helical coil spring 7 secured at one end thereof on the pawl 6 and hooked at an opposite end thereof on a lug 4f of the plate 4, the pawl 6 is biased in such a pivotal direction that the hook 6a is rendered out of engagement with the ratchet wheel 5.

The wire 11 is connected at one end thereof with the connecting portion 6c of the pawl 6 via a wire end 15. The wire 11 is provided in such a way that it extends upwards after being wound as many turns as needed on wirewinding portions 4c formed at outer peripheral - 14 edge portions of the plate 4. The opposite end of the wire 11 is connected with the unillustrated piston of the drive means 16.

A collision sensor is connected with the drive means 16. When a vehicle has undergone at least a predetermined 'magnitude of deceleration, this collision sensor detects the deceleration and outputs a detection signal. By this detection signal, an unillustrated gas generator disposed in the drive means 16 is triggered to produce gas in a cylinder and the piston is then operated by the pressure of the resulting gas. By the above operation of the piston, the wire 11 is pulled upwards (in the direction indicated by arrow X in FIG. l).

A description will next be made of operation of the pretensioner-equipped seat belt retractor described above.

Since the pawl 6 is out of engagement with the ratchet wheel 6 during normal running of a vehicle, the take-up spindle 2 is rotatable freely. Accordingly, the webbing 14 can be wound in under the biasing force of the take-up spring and can be wound out against the biasing force of the take-up spring.

When a certain magnitude of deceleration occurs on the vehicle as a result of sudden application of z - is brakes or the like, the occupant is caused move forward so that the webbing 14 is about to be wound out at a certain magnitude of acceleration. At this time, the emergency locking mechanism of the retractor is actuated to lock any further rotation of the take-up spindle. As a consequence, any further outward extension of the webbing is prevented. The drive means 16 however remains unactuated because the collision sensor does not output any detection signal.

When at least a predetermined, extremely large magnitude of deceleration occurs as in the event of a vehicular collision, on the other hand, the collision sensor detects the deceleration and outputs a detection signal. By this detection signal, the gas generator accommodated in the drive means 16 is triggered to produce gas in the cylinder and the piston is hence promptly moved upwards (in the direction indicated by the arrow X in FIG.1) by the pressure of the gas so produced. By the resulting drive force of the piston, the wire 11 is therefore pulled promptly in the direction indicated by arrow X. Since the plate 4 is held with its rotation being prevented at this time, pulling drive force of the wire 11, said pulling drive force having been applied to the connection portion 6c of the pawl 6, first causes the pawl 6 to pivot counterclock- 16 - wise as viewed in FIG. 1 against the biasing force of the helical coil spring 7 so that the hook 6a of the pawl 6 is brought into meshing engagement with one of the teeth 5a of the ratchet wheel 5. Because the wire 11 adapted to make the pawl to pivot is directly connected with the pawl member 6 in the illustrated embodiment, the meshing engagement between the hook 6a and one of the teeth 5a can be effected without fail- ure.

Further pulling of the wire 11 produces drive force so that at least a predetermined magnitude of rotary force is applied to the plate 4 via the pin 8. since the engaging beads 4a,4a are then unlocked from their corresponding holes 3b,3b against the biasing force of the disk spring 10, the plate 4 rotates in the direction of arrow Y as depicted in FIG. 4. At this time, the pawl 6 and the ratchet wheel 5 still remain engaged with each other, the ratchet wheel 5 rotates together with the plate 4 in the direction of arrow Y under the drive force of the wire 11.

As a result, the take-up spindle 2 rotates in the direction that the webbing 14 is wound in. The webbing 14 is therefore tightened so that play or slack of the webbing 14 can be eliminated.

In other words,- the plate 4, with which one end v of the wire 11 is connected, and the ratchet wheel 5 are brought into meshing engagement via the pawl 6, whereby no slip occurs therebetween. The take-up spindle 2 is therefore caused to rotate without failure and, moreover, the extent of rotation is constant. The occupant is therefore surely restrained under stabilized constant tightening force without substantial forward movement.

When the webbing is wound in a little further subsequent to the stoppage of the drive of the wire 11, the meshing engagement between the hook 6a and the tooth 5a is released because the pawl 6 is biased clockwise by the helical coil spring 7. The take-up spindle 2 is now rotatable independently from the plate 4. The occupant can therefore wind out the thustightened webbing 14 again and his emergency escape from the vehicle is therefore facilitated.

It is of course to be noted that the present invention is not limited to the above embodiment and various modifications are feasible on the basis of the principle of the present invention. For example, the shape of the plate 4 is not necessarily limited to such a shape as described above. Its engaging beads are not necessarily limited to the above-described conical shape. They may be formed into any shape insofar as their free ends are formed as tapered ends like hemispherical or pyramidal ends. A gear other than a ratchet wheel can also be used as the ratchet wheel 5. The hook of the pawl 6 can be formed into a shape corresponding to the shape of the teeth of the ratchet wheel.

The disk spring 10 for normally biasing the plate 4 toward the base side wall 3a and the helical coil spring 7 biasing the pawl 6 in the direction that the pawl 6 is not engageable with the gear 5 can be replaced by other biasing members, respectively. In addition, the drive means 16 is not limited to one making use of an explosive but drive means of other type, for example, one making use of spring force can also be used.

According to the pretensioner-equipped seat belt retractor according to the illustrated embodiment of this invention, the pawl which is engageable with the ratchet wheel is directly pivoted by drive force applied to the cable so that the meshing engagement of the hook of the pawl and one of the teeth of the ratchet wheel can be achieved without failure. Further, the plate, with which one end of the cable is connected, and the ratchet wheel are brought into meshing engagement via the pawl so that no slip occurs therebetween. Accordingly, the take-up spindle is surely rotated by the drive force applied to the cable and the amount of its rotation becomes constant. The occupant is therefore surely restraint under stabilized constant restraining force.

According to the construction of the illustrated embodiment, the pawl which is engageable with the ratchet wheel has a simpler shape and requires fewer parts compared with the conventional pretensioners, leading to improved assembling efficiency.

It is therefore possible to provide a pretensioner-equipped seat belt retractor which can achieve tightening of a wound webbing without failure in the event of emergency and which is simpler in construction, higher in assembling efficiency and lower in price.

- 20 1 2 3 4 6 7 8 9 12 13

Claims

CLAIMS: 1. A seat belt retractor having a pretensioner for bringing one end of a cable into engagement with a take-up spindle of the retractor in the event of a vehicular emergency whereby drive of the cable at an opposite end thereof causes the take-up spindle to rotate in such a direction as eliminating slack of a webbing, characterized in that said pretensioner comprises: a plate fitted on an end portion of the take-up spindle and rotatable when rotary force of at least a 11 predetermined magnitude is applied, a ratchet wheel secured on the end portion of the take-up spindle and rotatable together with the take-up 14 spindle, a pawl pivotally supported on the plate and normally biased in such a direction that the pawl is kept out of engagement with the ratchet wheel, and a cable wound around the plate and connected at one end thereof with the pawl and at an opposite end thereof with drive means; whereby the cable driven at the opposite end thereof by drive means brings the pawl into engagement with the ratchet wheel, thereby causing the take-up spindle to rotate together with the plate. 17 18 19 20 21 22 23 24 1 2 3 4 base, 6 7 8 2. A seat belt retractor having a pretensioner, characterized in that said retractor comprises: base, take-up spindle rotatably supported on the webbing fastened to the take-up spindle, ratchet wheel secured on the take-up spindle, a plate held on the base and movable relative to 9 the base when force of at least a predetermined mag nitude has been applied, 11 a pawl supported on the plate, movable between an 12 engagement position where the pawl is brought into 13 engagement with the ratchet wheel and a non-engagement 14 position where the pawl is kept out of engagement with the ratchet wheel, and biased toward the non-engagement 16 position, and 17 a cable connected at one end thereof with the 18 pawl and at an opposite end thereof with drive means; 19 whereby said drive means drives the cable in the event of a vehicular emergency so that the pawl is 21 first moved from the non-engagement position to the 22 engagement position and the take-up spindle is then 23 rotated in a webbing-winding direction.

1 3. A seat belt retractor of claim 2, wherein an engaging bead is formed on one of the plate and the 3 4

2

3 4 5 2 base and a matching recess is formed on the other of the plate and the base, and the retractor further comprises means for pressing the plate toward the base.

4. A seat belt retractor of claim 3, wherein the plate is loose-fitted on the take-up shaft so that the plate can rotate about the take-up spindle.

5. A seat belt retractor of claim 4, wherein the plate has a base portion opposing the base and an upright portion extending substantially at a right angle from a peripheral edge of the base portion, and the cable is wound on the upright portion.

1

6. A seat belt retractor of claim 1, wherein the pawl is pivotally supported on a pin which is disposed on the plate.

7. A seat belt retractor substantially as hereinbefore described with reference to, and as shown in, FIGS. 1 through 4 of the accompanying drawings.