FR2722155A1 - Belt roll-up device with pretensioner - Google Patents

Abstract

The belt roll-up device has an actuating element (6) for linear movement of a toothed rack (25) in a first direction. A pinion (21) engages with the rack in such a way that it revolves in a first rotational direction by movement of the rack in the first direction. A rotational drive element revolves in its first rotational direction by rotation of the pinion in its first direction. A take-up spindle (4) is mounted on a roller base and is pretensioned in the belt wind-up direction.

Description

 The present invention relates to a seat belt retractor having a pre-tensioning device, so that a set of a strap can be eliminated in the event of an emergency, by winding the strap on a winding journal of the reel.

 In a seat belt system designed to safely protect an occupant in a vehicle seat, the trend so far has been to reduce the winding force of the webbing of the retractor to make it feel less the occupant wears a strap. However, this inevitably results in greater slack in the strap, leading to the potential risk that, if great force is applied to the strap in the event of an emergency such as a vehicle collision, the strap can be pulled over a longer length and so it is lacking to effectively hold the body.

 In order to eliminate such play of the strap by winding the strap in the event of an emergency, reels have been proposed which are each provided with a pre-tensioning device assembled within them, to rotate instantly their winding pin in a winding direction.

 Such pre-tensioning devices include those of the type described, for example, in US Patent 5,364,168, issued November 15, 1994 to Muneo Nishizawa, et al., In which a drive member, such as a pulley is driven in rotation by the actuation of a drive means such as a traction cable drive assembly, for tightening the wound strap. The drive member for such a pre-tensioning device is connected to a winding pin, via an engagement means, so that, to avoid any interference with the rotation of the winding pin during normal use, the engagement means is kept out of contact with the winding pin, while the pre-tensioning device is not actuated but is connected to the winding pin to transmit a torque to the pin when the pre-tensioning device is actuated. The use of a gear similar to a gear, as a means of engagement, allows the drive member to efficiently transmit a torque to the winding journal.

On the other hand, the pre-tensioning device described, for example in the Japanese utility model (Kokoku)
No. 55-21696, published May 24, 1980, consists of a piston rod arranged for instant sliding movement in a cylinder by gas pressure and a rack which can engage against a gear rigidly fixed to a strap winding pin, in response to movement of the piston rod, so that the winding pin is rotated in a strap winding direction. When the piston rod and the rack are forced to move by gas pressure, when a vehicle collides, the rack is brought into contact with the gear, so that the gear is rotated to wrap the strap in the reel.

The construction, described above, of the pre-tensioning device described in US Patent No. 5,364,168
when a cable, such as a wire rope, is used as a means for transmitting a driving force from the driving means, for example, a piston as a rotational force for the winding journal - however requires taking counts an additional cable winding value, necessary to bring the drive member into contact with the winding pin, in addition to a cable winding value necessary to obtain a desired degree of tightness of the wound strap on the winding pin. It follows that a greater piston stroke is necessary, giving rise to a larger pre-tensioning device, so that the ability to mount the retractor on a vehicle is reduced. In addition, high pressure gas, produced by a gas generator, leaks through a gap between a wall of a wire rope sliding channel, in a manifold housing and the wire rope, so that the gas pressure cannot be used effectively as a driving force for the driving means.

 According to the construction described above of the pre-tensioning device described in the Japanese utility model (Kokoku) No. 55-21696, it is necessary to provide a rack stroke as large as the length of the strap to be tightened. Longer cylinders and racks are therefore required, giving rise to a larger pre-tensioning device, so that the suitability for mounting the reel on a vehicle is reduced.

 In addition, in the construction of each of these pre-tensioning devices, the pulley or the rack, after completion of its strap tightening operation, is not prevented from turning or moving in the direction of strap unwinding. . It is therefore impossible to prevent unwinding of the strap as long as the rotation of the winding pin in the direction of strap unwinding is prevented by a safety locking mechanism. By bringing the pulley and the winding pin or the rack and the gear, as aforementioned engagement means, into meshing contact in the event of a vehicle emergency situation, their teeth do not are not in contact with each other at an initial stage.

Their teeth can therefore be broken if the drive means is actuated and the teeth collide with each other at their tips.

 An object of the present invention is, therefore, to remedy the problems described above and to provide a compact seat belt retractor provided with a pre-tensioning device, said retractor being capable of effectively using a pressure of gas from a drive means and uniformly transmit a strap tightening drive force to a winding journal and also to prevent the extension of the strap at the end of a tightening operation the wrapped strap.

According to one aspect of the present invention, there is thus proposed a seat belt retractor having a pre-tensioning device, comprising
a rack;
drive means for forcing said rack to move rectilinearly in a first direction;
a pinion disposed in meshing contact with said rack, so that said pinion is rotated in a first direction of rotation by the movement of said rack in said first direction;
a rotary drive member, rotatable in said first direction of rotation by the rotation of said pinion in said first direction of rotation;
a reel base;
a winding pin mounted to rotate on said winder base and moved in a strap winding direction; and
a clutch mechanism disposed between said rotary drive member and said winding journal for transmitting rotation of said rotary drive member in said first direction of rotation to said winding journal, said clutch mechanism normally holding said member rotary drive and said winding journal in an unconnected state but, when said rotary driving member rotates in said first direction of rotation, bringing said rotary driving member and said winding journal to a connected state.

Preferably, the clutch mechanism may include
a clutch ring attached to the winding journal and having a circular outer circumference;
an element of engagement;
a support, mounted on the reel base and holding the engagement member in a predetermined position; and
a cam surface, formed on the rotary drive member and forming an angularly shaped gap, which flares in the first direction of rotation of the rotary drive member.

 The support may desirably be attached to the take-up base via means for producing rotational resistance between the support and the take-up base, when a torque of at least a predetermined value is applied by the element of engagement.

The resistance producing means may preferably include
a part of the retaining tab, which is normally kept in contact with an engaged part of a support base mounted on the reel base but, when a torque of at least a predetermined value is applied to the support, is released from engagement and is then brought into contact with the support base to produce friction resistance.

The resistance producing means may preferably include
an active member, formed on the support; and
an actuated member, fixed to the reel base and located on a path of movement of the active member, so that the actuated member is deformable by the active member.

 The active member may preferably be an edge part formed on the support, the actuated part is an annular rib of the support base and the annular rib is sheared by the edge part.

 The holder may preferably include a retaining finger for retaining the roller rod and openings are formed in the retaining finger, on portions opposite the clutch ring and the cam surface, respectively.

The seat belt retractor may further include
a speed acceleration gear transmission arranged between the pinion and the rotary drive member, so that the rotation of the pinion is transmitted at a higher speed to the rotary drive member.

The speed acceleration gear transmission may desirably include
a rotating disc arranged in meshing contact with the pinion;
an internal gear mounted on a reel base;
a planetary gear mounted rotating on a rod disposed on the rotary disc and maintained in meshing contact with the internal gear; and
an external gear arranged on the external periphery of the rotary drive member and maintained in meshing contact with the planetary gear.

 Preferably, the retractor base can be provided with a useful positioning means during the assembly of the planetary gear.

The seat belt retractor may further include
a return prevention mechanism, for preventing the rack from moving rectilinearly in a second direction which is opposite to the first direction of rectilinear movement.

The return prevention mechanism may preferably include
a rack gear case, having a cam surface and attached to the reel base, the cam surface forming an angular space widening in the first direction of rectilinear movement of the rack;
a claw arranged in the angular space; and
a displacement member moving the claw in a direction in which the angular space becomes narrower.

 When the rack is forced to move rectilinearly in the first direction by the drive means, the pinion is brought into meshing contact with the rack, so that the pinion is rotated in the first direction of rotation .

By the rotation of the pinion in the first direction, the rotary drive member is rotated in the first direction of rotation. This rotation of the rotary drive member is transmitted to the winding journal by the clutch mechanism, so that the winding journal is rotated in the direction of webbing winding.

 Even with a short rack stroke, the rack can fully rotate the winding journal in the strap winding direction.

The clutch mechanism is arranged between the winding journal and the rotary drive member, so that the teeth of the pinion and the rack can be brought into contact with one another, even during a step initial.

Various advantages and characteristics of the present invention will emerge from the detailed description below made in conjunction with the appended drawings, in which FIG. 1 is a front view of a reel of
seat belt fitted with a device
of pre-tension (which can be called
hereinafter "seat belt retractor
equipped with a pre-tensioning device "),
the seat belt retractor
concerning a first embodiment of
the present invention; Figure 2 is a fragmentary exploded view of
the seat belt retractor fitted
a pre-tensioning device, shown
in Figure 1; Figure 3 is another fragmentary exploded view of
the seat belt retractor fitted
a pre-tensioning device, shown
in Figure 1; Figure 4 is another fragmentary exploded view of
the seat belt retractor fitted
a pre-tensioning device, shown
in Figure 1; Figure 5 is a cross-sectional view of
the seat belt retractor fitted
a pre-tensioning device, shown
in Figure 1, taken in the direction of
VV arrows; Figure 6 is a cross-sectional view of
the seat belt retractor fitted
a pre-tensioning device, shown
in Figure 1, taken in the direction of
arrows VI-VI; Figure 7 is a cross-sectional view of
the seat belt retractor fitted
a pre-tensioning device, shown
in Figure 5, taken in the direction of
arrows VII-VII; Figure 8 is a fragmentary sectional view
transverse of the belt reel
security equipped with a pre device
voltage, shown in Figure 1, for
explain how a mechanism works
clutch illustrated in Figure 6; Figure 9 is an exploded fragmentary view of a
seat belt retractor fitted with
pre-tensioning device according to a second
embodiment of the present invention; Figure 10 is another fragmentary exploded view of
the seat belt retractor fitted
a pre-tensioning device shown on
Figure 9; Figure ll is a fragmentary view to larger
scale of a clutch mechanism in a
seat belt retractor fitted with
pre-tensioning device, according to a third
embodiment of the present invention; Figure 12 is a cross-sectional view of the
clutch mechanism shown in
figure 11, taken in the direction of
arrows XII-XII; Figure 13 is a fragmentary view to larger
scale to explain how the
clutch mechanism shown in
Figure 11; Figure 14 is a fragmentary view to larger
scale to explain how the
clutch mechanism shown in
Figure 11; Figure 15 is a fragmentary view to larger
scale to explain how the
clutch mechanism shown in
Figure 11; Figure 16 is a fragmentary view to larger
scale to explain how the
clutch mechanism shown in
Figure 11; Figure 17 is a fragmentary view to larger
scale of a clutch mechanism in a
seat belt retractor fitted with
pre-tensioning device, according to a fourth
embodiment of the present invention; Figure 18 is a cross-sectional view of the
clutch mechanism shown in
figure 17, taken in the direction of
arrows XVIII-XVIII; and Figure 19 is a cross-sectional view of the
clutch mechanism shown in
figure 17, taken in the direction of
arrows XIX-XIX.

 The seat belt retractor 1 equipped with a pre-tensioning device according to the first embodiment of the present invention is described below with reference to FIGS. 1 to 7.

 The seat belt retractor equipped with a pre-tensioning device designated by 1, is provided with a winding reel 7 on which a strap 20 is wound, so that the strap 20 can be wound or unwound. Analogously to conventional winders, the winding reel 7 is normally moved in one direction, in which the strap 20 is wound, by an elastic winding assembly 5 connected to a winding pin 4 of the reel. winding 7. As soon as the strap 20 is to be unwound at an acceleration of at least a predetermined value, the rotation of the winding journal 4 is prevented by a safety locking mechanism 2, so that the strap 20 cannot be of any other length.

 In the seat belt retractor 1 equipped with a pretensioning device, a pretensioning device 3 provided with a drive means for rotating the winding journal 4, in a direction in which any play of the strap 20 is eliminated, is placed on one of the side walls îîa of the reel base 11, produced substantially in a square U-shape. The pre-tensioning device 3 is provided with a clutch ring 12 external as a rotary drive member, capable of intermittently transmitting a torque to the winding pin 4, via a clutch mechanism 30, of a drive means 6 for rotating and driving the clutch ring 12 external by a pinion 21 maintained in meshing contact with a rack 25, which is pushed and driven by the pressure of a gas produced by a gas generator 29, of a planetary gear assembly 35 arranged as a transmission to mesh speed acceleration between the pinion 21 and the outer clutch ring 12, in order to rotate the outer clutch ring 12 at a higher speed during the rotation of the pinion 21, and of a control unit not illustrated, to activate the gas generator 29 in the event of a vehicle collision.

 The outer clutch ring 12 is a cylindrical member which is rotatably mounted relative to the winding pin 4 around a central axis of a clutch ring 14 having a circular outer periphery and mounted on an end portion of the winding pin 4, passing through the lateral wall pila, and which is rotated and moved by the drive means 6 via the planetary gear transmission 35, described below. On an outer peripheral surface are formed external teeth 12a to form a satellite gear arranged in contact with planetary gears 15 of the planetary gear assembly 35. In addition, four cam surfaces 12b are formed at identical intervals in an angular direction on an inner peripheral surface, formed by digging the outer clutch ring 12. Between the cam surfaces 12b and an outer peripheral surface of the clutch ring 14 are formed spaces of angular shape, which widen in the direction of rotation of the outer clutch ring 12. In each of the angular spaces, a cylindrical roller rod 10, which is a claw movable in the direction of engagement of the clutch ring 14, is arranged to allow the transmission of a torque between the clutch ring 12 outer and the clutch ring 14. In combination with a support 8 fixed as a holding means on the pila side wall, to prevent any displacement of the roller rods 10 in a clutch ring engagement direction, the rods roller 10 constitute the clutch mechanism 30 (see Figure 6).

 The support 8 is made of a synthetic resin-based material, such as polyacetate or nylon, or a metallic material such as aluminum or zinc, and is provided with a base plate portion 8a ring and four pairs of fingers for holding roller rods 9a, 9b. The base plate part 8a defines a circular hole into which the winding pin 4 is inserted. The holding fingers of the roller rods 9a, 9b are arranged perpendicularly on the base plate part 8a, so that the fingers holding rollers 9a, 9b extend along an axis of the base plate portion 8a. The roller rod holding fingers 9a, 9b respectively pass through holding slots 13a, 13b, which are formed in a side wall 11a, so that the roller rod holding fingers 9a, 9b extend towards outside of the side wall 11a. The base plate part 8a is therefore arranged on the reel so that the base plate part 8a is held between a flange part of the winding coil 7 and the side wall 11a. Tip parts of the retaining fingers of roller rods 9a, 9b are inserted into the respective angular spaces formed in the outer clutch ring 12, arranged on an outer side of the side wall 11a, so that the rods roller 10 are out of contact with the outer peripheral surface of the clutch ring 14.

 The inside diameter of the outer clutch ring 12 is greater than the outside diameter of the clutch ring 14 and the roller rods 10 held between the corresponding roller rod holding fingers 9a, 9b of the support 8 are arranged with a clearance with respect to the outer peripheral surface of the clutch ring 14. In fact, the roller rods 10 are maintained by the support 8 in a state where absolutely no torque can be transmitted.

 During normal use, therefore, the retractor itself creates a problem which is that, due to vibration or the like, the roller rods 10 held by the support 8 may come into contact with the clutch ring 14, to interfere with the unwinding or winding of the strap 20 from, or into, the reel, or the operation of the safety locking mechanism 2, or may produce an abnormal noise.

 Each pair of roller rod holding fingers 9a, 9b holds the corresponding roller rod 10 so that, in plan view parallel to the base plate portion 8a, the roller rod holding fingers 9a, 9b are facing each other and extending in the direction of the periphery of the base plate portion 8a. When the retaining fingers of the roller rods 9a, 9b in torque are produced as a single piece, the roller rod 10 is exposed at its external peripheral surface parts which are located opposite the clutch ring 14 and the corresponding cam surface 12b of the outer clutch ring 12. A rotational driving force in the strap winding direction is therefore applied to the outer clutch ring 12 and, even when the outer clutch ring 12 turns suddenly, the roller rods 10 can be kept stationary relative to the side wall lla. The roller rod holding fingers 9a, 9b can therefore limit the movement of the roller rods 10 in the angular direction, until the roller rods 10 are brought into contact with the ring securely. clutch 14.

 In addition, when the outer clutch ring 12 is rotated through a predetermined angle and the roller rods 10 are moved towards a central axis of the winding journal 4 by the respective cam surfaces 12b, the holding fingers roller rods 9a, 9b can easily be deformed so that the roller rod holding fingers 9a, 9b do not interfere with the movement of the roller rods in the direction of engagement. When the outer clutch ring 12 is still rotated in the strap winding direction, the roller rod holding fingers 9a, 9b are broken from the base plate portion 8a, so that the rods rollers 10 are brought into contact with the clutch ring 14 and rotate in the strap winding direction in one piece with the outer clutch ring 12. The clutch ring 14 is made of a more rigid material than the roller rods 10 and its outer peripheral surface has been knurled to facilitate its contact with the roller rods 10.

 According to a specific description, when a rotational driving force is applied in the direction of strap winding (the direction indicated by an arrow X1 in Figure 2) on the outer clutch ring 12 by means of drive 6 described below, the roller rods 10 are forced to enter between the cam surfaces 12b of the outer clutch ring 12 and the outer peripheral surface of the clutch ring 14, so that the roller rods 10 connect the clutch ring 14 and the outer clutch ring 12 to each other and that a torque of the outer clutch ring 12 is transmitted to the winding pin 4.

 The planetary gear assembly 35 comprises three planetary gears 15 disposed between internal teeth 16a, formed on a planetary gear housing 16 fixed to an outer face of the side wall îîa, and a rotary disc 17 serving as a support supporting these planetary gears 15. In the rotary disc 17 are formed through holes 17a in which the rods 19 as well as the planetary gears 15 are mounted there rotating, are inserted by adaptation, and a central hole 18 in which the pinion is mounted 21. The planetary gears 15 are forced to rotate by the rotary disc 17 which rotates in one piece with the pinion 21. Consequently, the outer clutch ring 12 is rotated at a greater speed, by rotation pinion 21.

 The drive means 6 has the rack 25 comprising rack teeth 25a, said rack teeth 25a being engaged with the pinion 21, a cylinder 24 comprising, movable within it the rack 25, and a gas generator housing 28 establishing communication between and connecting an end portion of the cylinder 24 and a gas blowing portion of the gas generator 29. A base end portion of the cylinder 24 is connected to a fixed rack gear case 22 to an outer wall of the planetary gear case 16. In the rack gear case 22 are formed a central hole 33, in which the pinion 21 is housed rotating, and a guide part 34 hollowed out placed in communication, at the level one of its parts, with a central opening 33 and adapted to guide the sliding movement of the rack 25. On an outer wall of the rack gear housing 22, a plate 23 in which an opening 23a is formed is arranged so that the plate 23 covers the pinion 21 and the rack 25. In the opening 23a extends a free end part of the winding pin 4.

 On an end part of the rack 25, said end part located on one side of the gas generator casing 2â, are arranged a damping member 26 made of synthetic resin, rubber or a metal with porosity and a piston 27, capable of sliding in the cylinder 24. High pressure gas produced by the gas generator 29 is supplied to the piston 27, via the gas generator casing 28. Depending on the design, the damping is not necessary, so the piston and the rack can be made as a single unit. In addition, an O-ring can be used as a damper to obtain the protective effects against gas.

 On a side wall portion of the recessed guide portion 34, the side wall portion located on a side opposite a rear surface 25b of the rack 25, is formed a cam surface 32 which in turn forms a space for angular shape, widening in the direction of movement of the rack 25 (that is to say the direction designated by the reference Y1 in FIG. 5). In the angular space are arranged a cylindrical roller rod 36 and a helical spring 31 moving the roller rod 36 in a rack engagement direction. The cylindrical roller rod 36, serving as a claw, limits the movement of the rack 25 in a return direction (that is to say the direction designated by the letter Y2 in FIG. 5) relative to the side walls and a bottom wall from the guide part 34 hollowed out from the rack gear housing 22. The roller rod 36 and the helical spring 31 therefore constitute a return prevention mechanism for the rack 25.

When the rack 25 moves in the strap winding direction (the direction designated by the helical 31, so that the movement of the rack 25 is not prevented.

 In addition, an initial positioning rod 37, provided to define an initial position of the rack 25 during its assembly, is inserted on the bottom wall of the hollow guide portion 34, to improve the ease of assembly of the rack 25 and the planetary gear assembly 35. The initial positioning rod 37 is made of resin and is easily broken when the rack 25 is driven under pressure. However, it should be noted that the initial positioning rod 37 is not essential.

 A description is given below concerning the operation of the seat belt retractor 1 equipped with a pre-tensioning device described above.

 During normal movement of a vehicle, the outer clutch ring 12 and the roller rods 10 are out of contact with respect to the clutch ring 14, as illustrated in FIG. 6, so that the spring winding can rotate freely. It is therefore possible to wind the strap 20 under the effect of the displacement force of the elastic winding assembly 5 and also to unwind the strap 20 against the displacement force.

 When a deceleration of the vehicle by at least a predetermined value takes place due to sudden braking or the like, the passenger is caused to tilt forward, so that the strap 20 is ready to be unwound at a certain acceleration . The safety blocking mechanism 2 of the reel operates at this time, so as to prevent rotation of the winding journal 4. it follows that the strap 20 is prevented from extending by any length. However, the control unit not shown does not operate the gas generator 29, so that the rack 25 is not pushed, that is to say is not driven.

 When a deceleration of at least one extremely large predetermined value takes place as in the case of a vehicle collision, on the other hand, the control unit not shown detects the deceleration to activate the gas generator 29. The gas generator 29 thus actuated blows the drive gas to the gas generator housing 28. The expansion pressure of the drive gas which has flowed into the cylinder 25 from the gas generator housing 28 then acts on the piston 27, so that the piston 27 pushes, in other words drives, via the damping member 27, the rack 25 in the strap winding direction. At this time, the damping member 26 can reduce a sudden application of the gas pressure on the rack 25.

 Since the piston 27 is designed to push and drive the rack 25, there is no need to provide the gas generator housing 28 with an opening in which a piston rod or the like extends to transmit a driving force . Consequently, the gas pressure acts almost entirely on the piston 27 without leakage and can be used effectively as a driving force for the rack 25.

 When the rack 25 is pushed and driven in the direction indicated by the arrow Y1 in FIG. 5, the pinion 21, maintained in meshing contact with the rack teeth 25a of the rack 25, is rotated and moved in the strap winding direction (i.e. the direction indicated by arrow X1 in Figure 5). Then, the rotary disc 37, which rotates in one piece with the pinion 21 (see FIG. 3), rotates in the direction of the arrow X1.

 The planetary gears 15 which are rotatably mounted on the rods 19, are held on the rotating disc 17 and, as shown in FIG. 6, the planetary gears 15 are in contact with the inner teeth 16a of the planetary gear housing 16 and also with the outer teeth 12a of the outer clutch ring 12. Consequently, the rotation of the rotary disc 16 in the direction of the arrow X1 forces the planetary gears 15 to rotate in the direction of the arrow X1 and again to rotate on their own axes while engaging the inner teeth 6a of the housing. planetary gear 16, so that the outer gear ring 12 is rotated at a higher speed in the direction of arrow X1. Consequently, the rotation of the pinion 21 in the direction of the arrow X1 is transmitted at a higher speed to the outer clutch ring 12 by the planetary gear assembly 35.

 When the outer gear ring 12 is rotated in the direction of arrow X1, the roller rods 10 are pushed towards the central axis of the winding journal 4 by the associated cam surfaces 12b. At this time, the holding rods of the roller rods 9a, 9b, due to their elasticity or plastic deformation, allow the displacement of the roller rods 10 towards the central axis of the winding journal 4, until the rods roller 10 engage securely between the outer peripheral surface of the clutch ring 14 and the respective cam surfaces 12b.

 When the roller rods 10 move to points where the roller rods 10 safely enter between the outer peripheral surface of the clutch ring 14 and the respective cam surfaces 12b, the rotation of the outer clutch ring 12b is transmitted to the clutch ring 14, so that the clutch ring 14 and the roller rods 10 rotate in the direction of the arrow X1 in one piece with the outer clutch ring 12. The retaining fingers of roller rods 9a, 9b are therefore broken, as shown in FIG. 8.

 When the pinion 21 is rotated and further moved in the webbing direction by the driving force of the rack 25, pushed and driven by the expansion pressure of the driving gas, the ring clutch 12 outside, which rotates at a higher speed in one piece, rotates and drives the clutch ring 14 in the direction of arrow Xî, via the roller rods 10, so that the pin d winding 4 is rotated in the direction of strap winding. Consequently, the strap 20 is wound up, so that any slack in the strap is eliminated.

 As a result, the rack 25 of the drive means 6, which can transmit rotation at higher speed to the winding journal 4 via the planetary gear assembly 35, can completely rotate the winding journal 4 in the strap winding direction, even if the rack travel is short. The rack 25 and the cylinder 24 can therefore be made short, which makes it possible to build the pre-tensioning device with small dimensions.

 Between the outer clutch ring 12, which constitutes the planetary gear assembly 35 and which is rotated at higher speed, and the clutch ring 14 fixed to the winding journal 4 is the mechanism d clutch 30 which keeps the outer clutch ring 12 and the clutch ring 14 disconnected as long as the pre-tensioning device is not actuated. The teeth of the pinion 21, the rack 25 and the planetary gear assembly 35 are already engaged at an initial stage, in which the pretensioner has not been actuated. When the rack 25 is suddenly pushed and driven by the expansion pressure of the drive gas, the aforementioned teeth do not collide at their tips. This makes it possible to avoid any breaking of the teeth and also to uniformly transmit a driving force from the driving means 6 to the winding pin 4.

When the push drive of the rack 25 by the expansion pressure of the drive gas stops, the winding pin 4 rotates in the strap release direction (i.e. the direction designated by the arrow X2 in FIG. 8) under the effect of a tensile force of the strap 20, so that the outer clutch ring 12 and the pinions 21 start to rotate in the opposite direction. The rack 25 is then ready to move in the return direction relative to the side walls and to the bottom walls of the hollow guide portion 34 (in the direction of the arrow Y2 in FIG. 5)
However, the roller rod 36 enters between the rear surface 25b of the rack 25 and the cam surface 32 of the recessed guide portion 34, so that the relative movement of the rack 25 in the return direction is prevented. The pinion 21 is therefore prevented from rotating in the opposite direction. The winding journal 4, which is integrally connected to the rotating disc 17, the planetary gear 15 and the outer clutch ring 12 by means of the roller rods 10, are therefore prevented from rotating in the direction strap release. Even immediately at the end of a tightening operation of the strap wound by the pre-tensioning device 3, the drive means 6 can consequently prevent any unwinding of the strap. The return prevention mechanism for the rack 25 can be arranged at any location, provided that a surface of the rack 25 and a surface of the roller rod (claw) 36 can be brought into contact with one another in the position initial.

 Referring now to Figures 9 and 10, the seat belt retractor equipped with a pre-tensioning device according to the second embodiment of the present invention is described below. In FIGS. 9 and 10, elements of a structure identical to those corresponding to the seat belt retractor 1 equipped with a pre-tensioning device, according to the first embodiment, are designated by reference symbols identical. A detailed description of these identical elements is therefore not necessary.

 Essentially like the seat belt retractor 1 equipped with a pre-tensioning device described above according to the first embodiment, the seat belt retractor equipped with a pre-tensioning device according to the second mode embodiment, designated by 50, comprises a pre-tensioning device on one of the side walls 51a of the reel base 51, substantially in the form of a square U. The pre-tensioning device is provided with a drive means 6 for rotating a winding pin 4 in a direction such that any play in the strap is eliminated. The pre-tensioning device uses a clutch mechanism 55 and a planetary gear assembly 60 instead of the clutch mechanism 30 and the planetary gear assembly 35 of the pre-tensioning device 6 of the first embodiment. production.

 The clutch mechanism 55 is provided with an outer clutch ring 12, roller rods 10 and, as a holding means, with a support 52. The outer clutch ring 12 has four cam surfaces 12b, so that angular spaces are formed between the respective cam surfaces 12b and an outer peripheral surface of a clutch ring 14. The roller rods 10 are arranged in the respective angular spaces of the friction ring. clutch 12 outside. The support 52 is fixed to the side wall Sla, so that the roller rods 10 are prevented from moving in a clutch ring engagement direction.

 The support 52 is made of a material based on synthetic resin, such as polyacetal or nylon, or in a metallic material, for example, an elastic thin sheet material, such as aluminum, zinc, steel. stainless steel or sheet steel, and is provided with a base plate portion 52a substantially in the form of a disc and four pairs of fingers for holding roller rods 53a, 53b extending along an axis of the base plate portion 52a, perpendicular to the base plate portion 52a. The base plate part 52a defines a circular hole, into which the winding pin 4 is inserted, and holes 52b, to facilitate mounting of the base plate part 52a on the reel base 51. The part of base plate 52a is fixed to a planetary gear case 16 and to a rack gear case 22 on an outer surface of the side wall 51a. Tip parts of the roller retaining fingers 53a, 53b are inserted into the corresponding angular spaces of the outer clutch ring 12, arranged on an outer face of the support 52, so that the roller rods 10 are held out of contact with the outer peripheral surface of the clutch ring 14. In addition, the base plate part 52 is also provided with positioning moldings 54, which are useful when assembling the planetary gears 15.

 The planetary gear assembly 60 includes planetary gears 15 and, as a carrier, a rotating disc 57 rotatably supporting the planetary gears 15. The planetary gears 15 are disposed between inner teeth 16a, which are formed on a housing d planetary gear 16 fixed to an outer surface of the support 52, and the outer clutch ring 12. In the rotary disc 17 are formed through holes 57a and a central hole 58. Rods 19 with the respective planetary gears 15 mounted for rotation are inserted with tight fit into the through holes 57a, respectively, and a pinion 59 is installed in the central hole 58. The planetary gears 15 are forced to rotate by the rotary disc 57 which rotates in one piece with the pinion 59. Consequently, the rotation of the pinion 59 forces the outer clutch ring 12 to rotate at a speed higher.

 From the relationship between the speed acceleration ratio of the planetary gear assembly 60 and the length of the wound strap to be tightened, the pinion engaged with the rack 25 cannot rotate fully over an angle of 3600, even if the rack 25 moves over its entire travel. In such a case, the pinion, analogously to the pinion 59 illustrated in FIG. 10, can have only a desired number of teeth and any remaining peripheral part of the latter has a cylindrical surface having a diameter equal to a base diameter of the pinion. It goes without saying that the profile of the central hole 58 of the rotary disc 57 has a shape corresponding to the profile of the pinion 59.

 The processes carried out during the assembly of the pre-tensioning device described above are described below, on the reel of the second embodiment.

 First, the outer clutch ring 12 and the planetary gears 15 are assembled on the support 52. Here, the outer clutch ring 12 is assembled together with the cam surfaces 12b in coincidence, in positions in which the roller rods 10 do not engage against the clutch ring 14, and the roller rods 10 are fixed to the retaining fingers of corresponding roller rods 53a, 53b. In addition, the planetary gears 15 are arranged relative to the support 52 by the positioning moldings 54. The positioning moldings 54 are short projections to define the initial positions of the planetary gears 15 during their assembly. Since each planetary gear 15 has a play in the direction of its axis and is easily released from the maintained state when the pre-tensioning device is actuated, the positioning moldings 54 have no harmful effect on the rotation of the planetary gear assembly 60.

 Then, the planetary gear case 16 is assembled. The inner teeth 16a have been machined so that, when assembling the planetary gear case 16, the planetary gear case 16 and the planetary gears 15 can be brought into contact when the holes in the planetary gear case 16 and the holes 52b of the support 52 have been brought into coincidence, the first holes as well as the last holes being both used to mount the planetary gear housing 16 and the support 52 on the side wall 51a of the reel base 51.

 The rotary disc 57 is then assembled. To define the initial position of the rack 25, the position of the rods 19 for rotationally supporting the planetary gears 15 and the phase of the teeth of the central hole 58 in which the pinion 59 is inserted are determined on the basis of the initial position of the rack 25. Incidentally, the rotating disc 57 and the pinion 59 can be formed in one piece from the start.

 As will be appreciated, the seat belt retractor 50 equipped with a pre-tensioning device according to the second embodiment can offer, in addition to advantages similar to those offered by the seat belt retractor 1 equipped with a pretensioning device according to the first embodiment, the advantage that the ease of assembly during assembly of the pretensioning device on the reel is significantly improved.

 Referring now to Figures 11 and 12, the clutch mechanism of the seat belt retractor equipped with a pre-tensioning device, according to the third embodiment of the present invention, is described below . In FIGS. 11 and 12, elements of a structure similar to those corresponding to the clutch mechanisms 30, 55 of the embodiments described above are designated by identical reference symbols. The detailed description of these identical elements is therefore not necessary.

 The clutch mechanism, designated by 70, is provided with an outer clutch ring 12, roller rods 10, a support plate 71, a support base 75 and an element of 78 annular spacing. The outer clutch ring 12 has four cam surfaces 12b which form angular spaces between the cam surfaces and an outer peripheral surface of a clutch ring 14. The roller rods 10 are arranged in the respective spaces of angular shape of the outer clutch ring 12. The support plate 71 and the support base 75, in combination, constitute a holding means fixed to a side wall 90a of a take-up base, so that the roller rods 10 are prevented from moving in one direction clutch ring engagement. The annular spacer 78 is disposed between the support plate 71 and the side wall 90a of the reel base.

 The support plate 71 is provided with a base plate portion 71a substantially in the form of a disc and elastic retaining fingers 71a, 72b. The base plate portion 71a defines a circular hole in which extends a winding pin 14 supported, via a bushing 79, on the side wall 90a of a reel base, while the retaining fingers 72a, 72b elastic are four pairs of curved shaped holding fingers, so that the holding fingers extend along an axis of the base plate portion 71a. Four parts of retaining tabs 74 formed at identical intervals on, and extending from, an outer peripheral edge of the base plate part 71a are held in contact with a groove 76 formed in the support base 75. When a torque, of at least a predetermined value, is applied to the elastic retaining fingers 72a, 72b, the support plate 71 can therefore rotate relative to the side wall 90a of the reel base, while meeting resistance to rotation. In addition, imprint portions 73 which, when a torque of at least a predetermined value is applied, are deformed and trigger disengagement of the portions of holding tabs 74 from the groove 76 and are formed in a peripheral edge inside of the base plate portion 71a.

 Tip parts of the elastic retaining fingers 72a, 72b are inserted into the respective angular spaces of the outer clutch ring 12 disposed outside of the clutch ring 14 and resiliently hold the roller rods 10 in the state where the roller rods 10 are kept out of contact with the outer peripheral surface of the clutch ring 14.

 Although not illustrated in the drawings, the support base 75 has an external profile similar to the support 52 of the second embodiment described above. The support base 75 is fixed to the planetary gear case 16 and to the rack gear case 22 and is fixed to the outer surface of the side wall 90a of the take-up base. Furthermore, the support base 75 is provided with four cylindrical engagement uprights 77 which are installed in corresponding locking holes formed in the side wall 90a of the take-up base, so that any movement of the support base 75 is prevented.

 The support plate 71, the support base 75 and the spacer 78 are made of a material based on synthetic resin, such as polyacetal or nylon or of a metallic material, for example, an elastic material made of thin sheet, such as aluminum, zinc, stainless steel or sheet steel. In particular, the support plate 71 must be made of a material which allows easy deformation of the elastic retaining fingers 72a, 72b.

 The operation of the clutch mechanism 70 is described below.

 During normal operation of a vehicle, the outer clutch ring 12 and the roller rods 10 are kept out of contact with the clutch ring 14, as shown in FIG. 13. When the pre-tensioning device is actuated and the drive means 6 described above rotates and drives the outer clutch ring 12 in the direction of arrow Xl, the roller rods 10 are moved towards the central axis of the winding journal by the corresponding cam surfaces 12b, as illustrated in FIG. 14. At this moment, the elastic retaining fingers 72a, 72b of the support plate 71, due to their resilient or elastic deformation, allow the displacement of the roller rods 10 towards the central axis of the winding journal, until the roller rods 10 securely enter between the outer peripheral surface of the clutch ring 14 and the respective cam surfaces 12b.

 When the roller rods 10 move to the points where the roller rods 10 can safely enter between the outer peripheral surface of the clutch ring 14 and the corresponding cam surfaces 12b, the rotation of the clutch ring 12 outer is transmitted to the clutch ring 14, so that the clutch ring 14 and the roller rods 10 rotate in the direction of arrow X1 in one piece with the outer clutch ring 12. As illustrated in FIG. 15, the imprint portions 73 of the support plate 71 are therefore deformed so that the portions of retaining tabs 74 begin to gradually separate from the groove 76 of the support base 75.

 When the outer clutch ring 12 rotates further, the imprint portions 73 are significantly deformed, as shown in Figure 16. In addition, the base plate portion 71a is also fully deformed. Consequently, the retaining tab portion 74 is completely detached from the groove 76 of the support base 75.

 Since the support base 75 is prevented from moving by the engagement posts 77 installed in the locking holes of the side wall 90a of the take-up base, at this time, the imprint portions 73 of the plate support 71 are deformed securely, so that the portions of holding tabs 74 can be detached from the groove 76 of the support base 75 without any problem.

 Furthermore, the elastic retaining fingers 72a, 72b of the support plate 71 are constructed so that the roller rods 10 can easily move towards the central axis of the winding journal, but encounter resistance when they move outward in a radial direction from the winding journal. According to a specific description, each of the elastic retaining fingers 72a, 72b in torque is curved and stretched on a radially outer side rather than in a position in which the associated roller rod 10 is roughly divided in two as seen in the radial direction of the support plate 71. The torque-elastic holding fingers 72a, 72b have, consequently, a higher rigidity on their radially outer sides, so that the roller rod 10 is prevented from sliding easily towards the outside in the radial direction. On the side opposite to the position in which the associated roller rod 10 is roughly divided in two, the opposite side being the side of the central axis of the winding journal, the elastic retaining fingers 72a, 72b mainly maintain the roller rod 10 associated under the effect of their elasticity.

 By the deformation to which the parts of the holding tabs 74 are subjected when they are detached from the groove 76 from the support base 75, the roller rods 10 are pressed forcibly against the clutch ring 14, so that their engagement is assured.

 When the outer clutch ring 12 is turned further by the drive means 6, the outer clutch ring 12 forces the clutch ring 14 to turn in one piece in the direction of arrow X1 via the rods roller 10, so that the winding pin 4 is wound in the strap winding direction. Therefore, the strap 20 is wound up, in a manner eliminating any play in the strap.

 Even after the outer clutch ring 12 has been rotated and the retaining tab portions 74 have detached from the groove 76, the retaining tab portions 74 are held in contact against an inner surface of the support base 75, so that a friction resistance is produced. Consequently, the support plate 71 rotates relative to the side wall 90a of the winder base, while meeting resistance to rotation. Therefore, it is possible to apply a constant rotational resistance to the roller rods 10 which move in the direction of arrow X1.

 In the clutch mechanism 70 according to the third embodiment, the roller rods can be brought immediately into contact again with the clutch ring 14 and the outer clutch ring 12, even if the roller rods 10 are taken between the clutch ring 14 and the outer clutch ring 12 come to separate for one reason or another.

Even when the driving force varies considerably as in the case immediately following the operation of the driving means, the roller rods 10 can still be maintained in engagement contact between the clutch ring 14 and the clutch ring 12 outside and the driving force of the outer clutch ring 12 can be safely transmitted to the clutch ring 14.

 Referring finally to Figures 17 and 18, the clutch mechanism of the seat belt retractor equipped with a pre-tensioning device according to the fourth embodiment of the present invention, is described below. In FIGS. 17 and 18, elements of a structure identical to those corresponding to the clutch mechanism 70, in the third embodiment, are designated by identical reference symbols. A detailed description of these identical elements is therefore not necessary.

 The clutch mechanism, designated 80, is provided with an outer clutch ring 12 and roller rods 10. The outer clutch ring 12 has four cam surfaces 12b which form angular spaces between the cam surfaces and an outer peripheral wall of a clutch ring 14. The roller rods 10 are arranged in the respective angular spaces of the at least one tongue part 84 is arranged so that the tongue part 84 extends from the outer peripheral edge (the illustrated embodiment is provided with a pair of tongue parts).

On the support base 85, an annular rib 86 having a cross section in the shape of an inverted square U, as shown in FIG. 19, is arranged as an actuated part so that the annular rib 86 extends from the support base 85. Therefore, the support plate 81 is placed together with the tongue portions 84 extending into corresponding holding opening portions 86a and is fixed to the support base 85. In addition, the support base 85 is provided with four cylindrical engagement posts 87 which are installed in corresponding blocking holes formed in the side wall 90a of the take-up base, so that any displacement of the support base 85 is prevented.

 An edge part 84a is produced in the form of an active member at one end of each tongue part 84. When a torque of at least a predetermined value is applied to the elastic retaining fingers 82a, 82b, the tongue portion 84 rotates, while shearing the annular rib 86. In fact, in a manner analogous to the support plate 71 provided in the third embodiment described above, the support plate 81 is designed so that when 'a torque of at least a predetermined value is applied, the support plate 81 can rotate relative to the side wall 90a of the winder base, while meeting a resistance to rotation.

 The support plate 81 and the support base 85 are made of a material based on synthetic resin, such as polyacetal or nylon or in a metallic material, for example an elastic thin sheet material, such as aluminum. , zinc, stainless steel or sheet steel. It is preferable to form the support plate 81 from a more rigid material than the support base 85. In other words, it is preferable to select materials according to a combination such that the tongue parts 84 can shear the annular ribs 86.

 The operation of the clutch mechanism 80 is described below.

 When the pre-tensioning device is activated and the drive means 6 described above forces the outer clutch ring 12 to turn in the direction of arrow X1, the roller rods 10 which are prevented by the plate support 81 to move in the direction of rotation, are moved towards the central axis of the winding journal by the corresponding cam surfaces 12b. At this time, the elastic retaining fingers 82a, 82b of the support plate 81, due to their resilient or elastic deformation, allow the displacement of the roller rods 10 towards the central axis of the winding journal, up to that the roller rods 10 securely enter between the outer peripheral surface of the clutch ring 14 and the respective cam surfaces 12b.

 When the roller rods 10 move to the points where the roller rods 10 can safely enter between the outer peripheral surface of the clutch ring 14 and the corresponding cam surfaces 12b, the rotation of the clutch ring 12 outer is transmitted to the clutch ring 14, so that the clutch ring 14 and the roller rods 10 rotate in the direction of arrow X1 in one piece with the outer clutch ring 12. When the force with which the roller rods 10 are made to rotate in the direction of the arrow X1 reaches at least a predetermined value and a torque of at least a predetermined value is applied to the holding fingers 82a, 82b elastic, the tongue portions 84 of the support plate 81 begin to rotate, while shearing the annular ribs 86.

 When the outer clutch ring 12 is turned further by the drive means 6, the outer clutch ring 12 rotates in one piece and drives the clutch ring 14 in the direction of arrow X1 via the rods roller 10, so that the winding pin 4 is rotated in the direction of strap winding. Consequently, the strap 20 is wound up so as to eliminate any play in the strap.

 Even if the support plate 81 begins to rotate at this stage, the tongue portions 84 shear the annular ribs 86 to produce shear strength, while the annular ribs 86 have not been completely sheared and are still in existence . Consequently, the support plate 82 rotates with respect to the side wall 90a of the reel base, while meeting resistance to rotation. Constant rotational resistance can therefore be applied to the roller rods 10 which move in the direction of arrow X1.

 In the clutch mechanism 80 according to the fourth embodiment, the roller rods 10, as in the clutch mechanism 70 produced according to the third embodiment, can also be brought immediately into contact with the ring again. clutch 14 and the outer clutch ring 12, even if the roller rods 10 engaged between the clutch ring 14 and the outer clutch ring 12 come to separate for one reason or another.

Even when the driving force varies considerably as in the case immediately following the actuation of the driving means, the roller rods 10 can still be maintained in engagement contact between the clutch ring 14 and the clutch ring 12 outer and the driving force of the outer clutch ring 12 can be safely transmitted to the clutch ring 14. By changing the number of tongue portions 84 or the length of the annular ribs 86 made as parts to be sheared, it is possible to establish an angular stroke which provides optimum resistance to rotation.

 In the fourth embodiment described above, the edge portions 84a serving as active members shear the annular ribs 86 serving as actuated or passive portions. Instead of such shearing, the active members can cause plastic deformation of the passive parts.

 It goes without saying that the clutch mechanism, the speed acceleration gear transmission, the return prevention mechanism and the like of the present invention are not limited to the constructions of the respective embodiments described above and can have different structures.

 For example, the clutch mechanism of the present invention is not limited to the constructions of the clutch mechanism 30, 55, 70 and 80 of the respective embodiments described above and, to the extent that the objects of the present invention can be achieved, any known clutch mechanism can also be used.

Although the above embodiments of the present invention have been described using cylindrical roller rods provided as engagement members, spherical engagement members may also be used. Further, the constructions and shapes of the cam surface of the outer clutch ring as a rotary drive member, the support means, the fixing means for the support means, and the like can be changed at will.

 According to the seat belt retractor equipped with a pre-tensioning device, according to each of the embodiments described above of the present invention, the rack is pushed by the gas pressure to rotate the pinion in the case vehicle collision.

Therefore, there is no need to provide the gas generator housing with an opening in which a piston rod or the like extends to transmit a driving force. Therefore, gas pressure is effectively used almost entirely as the driving force for the rack. In addition, the rotation of the pinion is increased by the speed acceleration gear transmission and is then transmitted at the thus increased speed to the rotary drive member, so that the rack can rotate the winding journal completely. in the direction of strap winding with a short rack stroke. Consequently, the pre-tensioning device can be of compact construction.

 The clutch mechanism is arranged between the winding journal and the rotary drive member. The pinion, the rack and the gears constituting the speed acceleration gear transmission can be maintained in such a state that their teeth are engaged with each other, even in an initial stage. Even if the rack is suddenly pushed by the expansion pressure of the drive gas, the teeth of the individual gears do not collide at their tip parts. Therefore, it is possible to prevent breakage of the teeth and also to uniformly transmit the driving force to the winding journal.

 Therefore, it is possible to provide a compact seat belt retractor equipped with a pre-tensioning device which can effectively use the gas pressure of the driving means, which can uniformly transmit a driving force which is necessary to tighten the wound strap, to the winding pin, and which can also prevent any further unwinding of the strap at the end of the tightening operation of the wound strap.

Claims (16)

 1. Seat belt retractor having a pre-tensioning device, comprising  a rack (25);  drive means (6) for forcing said rack (25) to move rectilinearly in a first direction;  a pinion (21) disposed in meshing contact with said rack, so that said pinion is rotated in a first direction of rotation by the movement of said rack in said first direction;  a rotary drive member (12) rotatable in said first direction of rotation by the rotation of said pinion in said first direction of rotation;  a reel base (11);  a winding pin (4) mounted to rotate on said winder base and moved in a strap winding direction; and  a clutch mechanism (30) disposed between said rotary drive member (12) and said winding pin (4) for transmitting the rotation of said rotary drive member in said first direction of rotation to said winding pin, said clutch mechanism normally maintaining said rotary drive member (12) and said winding journal (4) in an unconnected state but, when said rotary drive member rotates in said first direction of rotation, bringing said member rotary drive and said winding pin in a connected state.  2. A seat belt retractor according to claim 1, further comprising  a speed acceleration gear transmission (35) arranged between said pinion (21) and said rotary drive member (12) so that the rotation of said pinion is transmitted at a higher speed to said drive member rotary.  The seat belt retractor according to claim 2, wherein said speed acceleration gear transmission (35) comprises  a rotary disc (17) arranged in meshing contact with said pinion (21);  an internal gear (16a) mounted on a reel base;  a planetary gear (15) rotatably mounted on a rod (19) disposed on said rotary disc and maintained in meshing contact with said internal gear; and  an external gear (12a) arranged on the external periphery of said rotary drive member (12) and maintained in meshing contact with said planetary gear (15).  4. Seat belt retractor according to claim 3, characterized in that said retractor base (11) is provided with positioning means (54) useful during the assembly of said planetary gear (15).  5. Seat belt retractor according to claim 3, characterized in that said pinion (21) has only the number of teeth necessary and any circumferential part remaining of the latter has a cylindrical surface having a diameter equal to a base diameter of said pinion.  The seat belt retractor according to claim 1, further comprising  a return prevention mechanism, for preventing said rack (25) from moving rectilinearly in a second direction which is opposite to said first direction of rectilinear movement.  The seat belt retractor according to claim 6, wherein said return prevention mechanism comprises  a rack and pinion gear housing (22), provided with a cam surface (32) and attached to said reel base (11), said cam surface (32) forming an angularly shaped space flaring in the first direction of rectilinear movement of said rack (25);  a claw (36) disposed in said angularly shaped space; and  a movement member (31) moving said claw in a direction in which said angular space becomes narrower.  8. Seat belt retractor according to claim 7,  further comprising  an initial positioning member (37) for defining an assembled position of said rack (25) in said first direction of rectilinear movement of said rack (25).  9. A seat belt retractor according to claim 1, wherein said clutch mechanism (30) comprises  a clutch ring (14) fixed to said winding journal (4) and having a circular outer circumference;  an engagement element (10);  a support (8), mounted on said retractor base (11) and holding said engagement member (10) in a predetermined position; and  a cam surface (12b) formed on said rotatable drive member (12) and forming an angularly shaped spacing which flares in said first direction of rotation of said rotary drive member (12).  10. Seat belt retractor according to claim 9, characterized in that said support (71, 81) is fixed to said retractor base (90a) via means for producing a rotational resistance between said support and said base d rewinder, when a torque of at least a predetermined value is applied by said engagement element (10).  11. Seat belt retractor according to claim 10, characterized in that said resistance production means comprises  a holding tab part (74), which is normally kept in contact with an engaged part (76) of a support base (75) mounted on said reel base (90a) but, when a torque at least a predetermined value is applied to said support (71), is released from engagement and is then brought into contact with said support base, to produce friction resistance.  12. Seat belt retractor according to claim 10, characterized in that said resistance producing means comprises  an active member (84a) formed on said support (81); and  an actuated member (86), fixed to said reel base (90a) and located on a path of movement of said active member (84a), so that said actuated member is deformable by said active member (84a).  13. Seat belt retractor according to claim 12, characterized in that said active member is an edge part (84a) formed on said support (81), said actuated part is an annular rib (86) of said support base (85) and said annular rib (86) is sheared by said edge portion (84a)  14. Seat belt retractor according to claim 9, characterized in that said support (8) comprises a retaining finger (9a, 9b) for retaining said roller rod (10) and openings are formed in said retaining finger on portions opposite to said clutch ring (14) and said cam surface (12b), respectively.  15. Seat belt retractor according to claim 1, characterized in that said drive means comprises a gas generator (29), a cylinder (24) accommodating, displaceable within it, said rack (25), and a gas generator housing (28), establishing communication between, and connecting said cylinder and a gas blowing portion of said gas generator; and said rack (25) is pushed and driven by a gas pressure produced by said gas generator, such that said rack (25) moves rectilinearly in said first direction of rectilinear movement.  16. Seat belt retractor according to claim 15, characterized in that said rack (25) is provided, via a damping member (26), with a piston (27) on a side proximal to said gas generator ( 29), and the gas produced by said gas generator acts on said piston (27).