JP3218987B2 - Pretensioner for seat belt retractor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retracting mechanism for a retractor for a seat belt which is driven by a driving means which is rotatable in association with a retractor for a seat belt in an emergency such as a vehicle collision. The present invention relates to a pretensioner for a seat belt retractor that rotates in a direction in which slack is removed.

[0002]

2. Description of the Related Art Conventionally, in a seatbelt device for holding a vehicle occupant's body safely in a seat, a retractor has a low force to wind the seatbelt in order to reduce the occupant's seatbelt wearing feeling. Tend to. As a result, the slack of the seat belt attached to the occupant's body increases, and when a large force is applied to the seat belt in an emergency such as a vehicle collision, the amount of extension of the seat belt increases, effectively restraining the occupant's body. There was something I could not do. Therefore, in order to wind up the seatbelt in an emergency and remove the slack, a retractor for a seatbelt with a pretensioner that incorporates a pretensioner that instantaneously rotates the winding shaft of the retractor in the winding direction is adopted. Is being developed.

[0003] As the pretensioner as described above, for example, a pinion gear provided to be rotatable in association with a winding shaft of a sheet belt retractor, a rack meshed with the pinion gear, and a slide in a cylinder are provided. And a piston connected to the base end of the rack, and in an emergency such as a vehicle collision, the rack is instantaneously pressed and driven by applying gas pressure to the piston, so that the pinion gear is driven. There have been developed various types in which the winding shaft of the retractor is rotated in a direction in which the slack of the seatbelt is removed through the retractor (Japanese Patent Laid-Open No. Hei 6-1994).
156187, Japanese Utility Model Publication No. 55-21696). In this form, the driving means mounted so as to be able to rotate in conjunction with the winding shaft is formed of a pinion gear and a rack.

Further, in a recent seat belt retractor, when slack is removed by a pretensioner and the tension applied to the seat belt is increased to a certain level or more, the seat belt is extended and an impact on an occupant is increased. A device equipped with an energy absorbing mechanism to mitigate the problem has been developed. As the energy absorbing mechanism, a webbing itself used as a seat belt is extended by a certain tension or more, or a retractor winding shaft is torsionally deformed. There has been proposed a device that reverses the winding shaft of the retractor when the tension acting on the retractor exceeds a certain level.

[0005]

However, in the event of an emergency, the driving means is instantaneously driven by applying gas pressure to the piston to move the winding shaft of the retractor in a direction in which the slack of the seat belt is removed. If the conventional pretensioner of the type in which the retractor is rotated is rotated in combination with an energy absorbing mechanism that reverses the winding shaft of the retractor when the tension acting on the seatbelt exceeds a certain level, there is a possibility that inconvenience may occur.

[0006] It is for the following reason. In general, in the pretensioner of the above type, the airtightness between the piston and the cylinder and the airtightness of the joint between the cylinder and the gas generator case are increased so that the gas pressure effectively works on the pressing drive of the piston. We are devising. As a result, the gas that has pressed the piston remains in the cylinder afterwards, and remains in the cylinder when the energy absorbing mechanism is activated to reverse the retractor winding shaft. The gas pressure increases with the rise of the piston and acts as a load that prevents the winding shaft from reversing. As a result, the energy absorption mechanism cannot secure the original amount of extension of the seatbelt, or the effect of reducing the impact on the occupant due to the delay of the extension speed of the seatbelt is reduced. However, there is a possibility that the effect cannot be sufficiently exerted.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems. In an emergency, a gas pressure is applied to the piston to instantaneously drive a driving means connected to the piston, thereby winding the retractor. A pretensioner that rotates the shaft in the direction in which the slack of the seat belt is removed, and when combined with an energy absorbing mechanism that reverses the retractor winding shaft when the tension acting on the seat belt exceeds a certain level, the piston An object of the present invention is to provide a pretensioner for a seatbelt retractor that can exert a sufficient effect on the energy absorbing mechanism without the gas pressure acting on the energy absorbing mechanism obstructing the operation of the energy absorbing mechanism.

[0008]

According to the present invention, there is provided a pretensioner for a seat belt retractor according to the present invention, which is ignited in an emergency such as a vehicle collision to generate gas, and A cylinder to which gas generated from the gas generator is guided, and a piston movably housed in the cylinder and driven to be pressed by the pressure of the gas,
A driving means for rotating the winding shaft of the seat belt retractor in a direction in which the seat belt is loosened by the movement of the piston. A sheet used in combination with an energy absorbing mechanism for reversing the winding shaft when the tension acting on the seat belt exceeds a certain level.
In the pretensioner of the retractor for Toberto,
The piston is provided with a gas vent hole which penetrates along the moving direction of the piston. Further, in the above configuration, it is preferable that the degassing means is constituted by a small hole having a diameter of about 0.6 mm to 1.2 mm. Further, in the above configuration, the driving means is based on a pinion gear mounted to be rotatable with the winding shaft of the seat belt retractor in an emergency such as a vehicle collision, and a piston slidably held in a cylinder. At the end, a rack tooth meshing with the pinion gear is provided at the front end side, and is pressed and driven by gas pressure acting on the piston in an emergency, and the winding shaft of the retractor is seated through the pinion gear to the seat. And a rack that rotates in a direction in which the slack of the belt is removed. Still further, in the above configuration, as the gas venting means, a first gas vent hole penetrating from a base end surface to a side surface closer to the base end is provided at a base end of the rack, and the first piston is provided at the piston. It is preferable to provide a second gas vent hole penetrating the piston along the sliding direction of the piston so as to communicate with the gas vent hole.
Further, in the above-mentioned configuration, a packing having a rack insertion hole into which the rack is slidably fitted and an outer peripheral portion elastically in contact with an inner peripheral surface of the cylinder is fitted to a base end of the rack. The packing is set so that the sliding resistance between the outer peripheral portion and the cylinder is greater than the sliding resistance between the rack insertion hole and the rack, and the degree of elastic contact of the outer peripheral portion with the cylinder is set. When the rack is fitted to the rack at a position circumscribing the piston, the rack insertion hole is so positioned that the inner peripheral surface of the rack insertion hole that is in close contact with the side surface of the rack closes the opening of the rack side surface of the first gas vent hole. It is even more preferable to set

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments. 1 to 5 show an embodiment of a pretensioner for a seat belt retractor according to the present invention. FIG. 1 is an exploded perspective view of a pretensioner 3 of one embodiment, and FIG. Pretensioner 3A
FIG. 3 is an enlarged view showing a configuration of a gas release mechanism of a pretensioner 3A according to an embodiment, and FIG.
Is an explanatory view of the arrangement of a stopper provided in a pretensioner 3A of one embodiment, and FIG. 5 is an explanatory view of the operation of a stopper provided in a pretensioner 3A of another embodiment of the present invention.

[0010] The pretensioner 3A according to this embodiment.
Is installed on the vehicle seat belt retractor,
It is a rotary drive member that removes slack of the seat belt in an emergency such as a vehicle collision and can transmit torque intermittently to a winding shaft 4 (see FIG. 2) of a retractor via a clutch mechanism (not shown). A clutch outer wheel (not shown) and a rack 25 which is pressed and driven by the gas pressure generated by the gas generator 29
And the pinion gear 2 always meshed with the rack 25
1, a driving means 6 for rotating and driving the clutch outer wheel, and a planetary gear device (shown as a speed increasing gear transmission) disposed between the pinion gear 21 and the clutch outer wheel for rotating the clutch outer wheel at an increased speed by rotation of the pinion gear 21. Omitted)
And a control device (not shown) for operating the gas generator 29 at the time of a vehicle collision. Further, the pretensioner 3A of this embodiment includes an energy absorbing mechanism (not shown in the drawings) that reverses the winding shaft 4 when the tension applied to the seatbelt becomes equal to or more than a predetermined value after the slack of the seatbelt is removed by the pressing drive of the rack 25. ) Are combined.

The driving means 6 includes a pinion gear 21, a rack 25 formed with rack teeth 25 a meshed with the pinion gear 21, a cylinder 24 movably receiving a base end of the rack 25, and a distal end of the cylinder 24. And a gas generator case 28 for communicating and connecting the gas generator 29 with a gas ejection portion. The flange 24 a at the base end of the cylinder 24 has the concave groove 22 of the rack gear case 22.
By being fitted to a, it is connected to the rack gear case 22.

The rack gear case 22 includes:
Central opening 33 in which pinion gear 21 is rotatably housed.
And a guide groove 34 for slidingly guiding the rack 25 in partial communication with the central opening 33, and an opening 23 a through which the tip of the winding shaft 4 penetrates outside the rack gear case 22.
Is disposed so as to cover the pinion gear 21 and the rack 25.

The base end of the rack 25 received in the cylinder 24 is connected to a piston 40 which receives gas pressure supplied from the gas generator 29 into the cylinder 24 through the gas generator case 28. Have been. That is, the pretensioner 3A of this embodiment is injected from the gas generator 29 in an emergency such as at the time of a vehicle collision, and
By pressing and driving the rack 25 with the gas pressure acting on 0, the winding shaft 4 of the retractor is rotated in a direction in which the slack of the seat belt (webbing) is removed.

In this embodiment, the piston 40
Is a piston body 4 integrally formed at the base end of the rack 25.
1 and a pressure receiving plate 27 that is superposed on the piston main body 41 and that transmits the gas pressure supplied into the cylinder 24 to the piston main body 41. The piston body 41 is formed integrally with the rack 25 by a suitable metal such as an aluminum alloy, but the pressure receiving plate 27 is formed by a synthetic resin or a metal such as aluminum.

A ring-shaped seal member 26 for maintaining airtightness between the piston 40 and the cylinder 24 is provided.
Is held between the piston body 41 and the pressure receiving plate 27.

In the pretensioner 3A of this embodiment, after the rack 25 is pressed and driven by the gas pressure generated by the gas generator 29 via the piston 40 to remove the slack in the seat belt, the energy (not shown) A gas venting mechanism 45 is provided so that the gas pressing the piston 40 does not hinder the operation of the energy absorbing mechanism when the absorbing mechanism operates. As shown in FIG. 3, the degassing mechanism 45 includes a first degassing hole 4 formed in a base end of the rack 25.
6 and a second gas vent hole 47 formed in the piston 40.

The first gas vent hole 46 penetrates from the base end surface of the rack 25 to a side surface near the base end. The second gas vent hole 47 is formed in the piston main body 41 and the pressure receiving plate 27 so as to communicate with the first gas vent hole 46 so that the small gas holes 41 a and 27 a along the sliding direction of the piston 40.
Is penetrated. The vertical hole 46a of the first gas vent hole 46 and the small diameter holes 41a and 27a of the piston body 41 and the pressure receiving plate 27 each have a diameter of 0.6 to 1.2.
mm. In addition, the first gas vent hole 4
The lateral hole 46b opening on the side surface of the hole 6 is a large-diameter hole having a diameter several times that of the vertical hole 46a. Further, on the side of the piston main body 41 of the pressure receiving plate 27, a concave portion 27b having an increased diameter is formed for ensuring communication between the small-diameter holes 41a and 27a.

In this embodiment, as shown in FIG. 2, the rack 25 has a positioning inclined surface 5 formed on the inner surface of the top of the cylinder 24 and a pressure receiving plate 2 of the piston 40.
7 is set in a predetermined initial position by assembling the abutment 7 with the abutment 7. The rack 25 assembled at the initial position has a state in which the rack 25 teeth 25 a at the tip end are engaged with the pinion gear 21.

In the case of the pretensioner 3A of this embodiment, if the tension applied to the seat belt becomes higher than a specified value after a predetermined slack is removed by pressing the rack 25 in an emergency, the illustration is omitted. The actuation of the energy absorbing mechanism allows the winding shaft 4 of the retractor to rotate in the direction in which the seat belt extends, whereby the pinion gear 21 rotates in reverse in conjunction with the winding shaft 4 to remove the slack in the amount of sheet removed. The belt can be pulled out.

Further, in the case of this embodiment, when the rack 25 is returned to the initial position by the tension applied to the seat belt, if the driving torque acting on the pinion gear 21 in the reverse direction is equal to or more than a specified value, An engagement release mechanism 7 that releases the engagement between the rack 25 and the pinion gear 21 and allows the seat belt to further extend due to the reverse rotation of the pinion gear 21 is provided.

The disengagement mechanism 7 includes a pinion gear 21
When the driving force acting on the rack 25 by the driving torque in the reverse rotation direction is not less than a specified value, as shown in FIG. 4, the inclined surface 5 and the pressure receiving plate 27 which are members for positioning the rack 25 at the initial position are deformed or damaged. By doing so, the rack 25 is further retracted from the initial position, and the engagement between the rack 25 and the pinion gear 21 is released.

As shown in FIGS. 4 and 5, one side of a guide groove 34 for slidingly guiding the rack 25 is provided with a rack 25.
Is provided with a stopper 9 that protrudes into the sliding path of the rack 25 when the slider 25 has departed from the initial position by a certain distance and restricts the rack 25 from returning to the initial position.

In the above pretensioner 3A, since the gas venting mechanism 45 is formed in an elongated narrow tube shape, when the gas tries to pass through the gas venting mechanism 45 at high speed, the pressure inside the cylinder is quickly reduced due to the viscous resistance of the gas. The pressure can be maintained until the pretensioner operates without falling.
Also, there is sufficient time before the energy absorbing mechanism operates and during operation, and the internal pressure can be reduced to a necessary and sufficient value. Because, usually, the operation time of the pretensioner is very short and there is no 10 msec, and after that, it takes about 15 msec until the energy absorption mechanism operates, and the operation time of the energy absorption mechanism is also 20 to 60 ms.
This is because ec will continue. Also, unlike the gap between the piston and the cylinder, the gas venting mechanism 45 of the pretensioner 3A has an elongated narrow tube shape, so that it is easy to control the cross-sectional area and shape of the penetrating portion, and when the pretensioner is activated. As described above, it is possible to more reliably perform the pressure holding in a short time, the time until the operation of the energy absorbing mechanism and the sufficient release of the pressure during the operation. Therefore, the piston is pressed and driven as designed by the action of the gas pressure in an emergency, and the slack of the seat belt can be reliably removed.

Further, according to the above pretensioner 3A, the rack 25 is in the initial position at the tooth 2 at the tip of the rack 25.
5a is configured to mesh with the pinion gear 21, and it is not necessary to equip both ends of the rack 25 with a portion having no teeth.
It is possible to minimize the moving range of 5
By reducing the size of the rack 25 meshing with the pinion gear 21, the size of the device can be reduced. In addition, since the rack 25 and the pinion gear 21 are already meshed at the initial position, the pinion gear 21 and the rack 25 do not mesh with each other when the rack 25 is pressed and driven by gas pressure, and the rack 25 is damaged by the shock. Can be avoided.

Moreover, when the pinion gear 21 is reversed by the tension applied to the seat belt and the rack 25 is returned to the initial position after the predetermined slack removal processing by the pressing operation of the rack 25, the reverse rotation acting on the pinion gear 21 is performed. If the driving torque in the direction is equal to or greater than the specified value, the mesh release mechanism 7
As a result, the engagement between the rack 25 and the pinion gear 21 is released, and further extension of the seat belt due to the reverse rotation of the pinion gear 21 is allowed, so that the energy absorbing mechanism provided in the retractor can secure a sufficient stroke. Will be possible.

Hereinafter, another embodiment of the present invention will be described with reference to FIGS. 6 to 10 show another embodiment of the pretensioner for a seat belt retractor according to the present invention. FIG. 6 is an exploded perspective view of a pretensioner 3B of another embodiment, and FIG. FIG. 8 is a cross-sectional view showing an initial state of a pretensioner 3B of the embodiment, FIG. 8 is an enlarged view showing a configuration of a gas release mechanism of the pretensioner 3B of another embodiment, and FIG. 9 is a disengagement of the pretensioner 3B of another embodiment. FIG. 10 is an enlarged view showing the operation of a gas release mechanism of a pretensioner 3B according to another embodiment. As shown in FIGS. 6 to 10,
The pretensioner 3B according to another embodiment of the present invention further uses a packing 48 described later in order to more reliably hold the gas pressure in the cylinder and release the gas, and the other configuration is the same as that of the above-described one. Since the pretensioner is the same as the pretensioner 3A of the embodiment, members having the same configuration or the same operation are denoted by the same reference numerals, and the description thereof is omitted.

As shown in FIGS. 6 to 8, the gas venting mechanism 55 has a first gas venting hole 46 formed in the base end of the rack 25 and a second gas venting hole formed in the piston 40, as shown in FIG. 2 and a rubber gasket 48 fitted to the base end of the rack 25.

The packing 48 includes a rack insertion hole 48a into which the rack 25 is slidably fitted, and an outer peripheral portion 48b elastically contacting the inner peripheral surface of the cylinder 24. The packing 48 has a sliding resistance between the outer peripheral portion 48b and the cylinder 24, and the rack insertion hole 48a and the rack 2 have a sliding resistance.
5 so as to be larger than the sliding resistance between them.
The degree of elastic contact of the cylinder 8b with the cylinder 24 is set. As shown in FIG. 8, when the packing 48 is fitted to the rack 25 at a position circumscribing the piston 40, the rack insertion hole 48 a
The rack insertion hole 48a is set so that the inner peripheral surface of the rack hole closes the opening of the first gas vent hole 46 on the side surface of the rack 25.
When the rack 25 is at the initial position, the packing 48
Is located at a position circumscribing the piston 40.

In the above pretensioner 3B, when the rack 25 is at the initial position, as shown in FIG. 7, the first vent hole 46 formed through the rack 25 is closed by the packing 48, and Sometimes gas pressure is piston 40
Is prevented from leaking from the second gas vent hole 47 formed in the piston 40 to the first gas vent hole 46 when acting on the piston 40. Therefore, the gas pressure generated by the gas generator 29 works to push down the piston 40 without waste. When the piston 40 is driven by the gas pressure, the packing 48 is maintained in the initial state in contact with the piston 40, so that the closing of the first gas vent hole 46 by the packing 48 is released during the pressing drive. Not even. Therefore,
The rack 25 is pressed and driven as designed by the action of the gas pressure in an emergency, and the slack of the seat belt can be reliably removed.

Further, after the removal of the slack in the seat belt is completed, the tension acting on the seat belt becomes higher than a predetermined value, the energy absorbing mechanism is operated, and the pinion gear 21 meshed with the rack 25 is reversed. 9 and 10, since the rack 25 meshing with the pinion gear 21 rises to the initial position with the reverse rotation of the pinion gear 21, the packing 48 has a large sliding resistance (friction) with the cylinder 24. As shown in FIG.

That is, when the energy absorbing mechanism operates and the rack 25 starts to rise due to the reverse rotation of the pinion gear 21, the packing 48 shifts from the position in contact with the piston 40 toward the tip end of the rack 25 at the initial stage. The blockage of the first vent hole 46 is released. Therefore, the pinion gear 2
When the rack 25 is moved upward by the reverse rotation of the cylinder 1, the gas remaining in the cylinder 24 and the gas generator case 28
From the gas vent hole 47 through the first gas vent hole 46 to the rack 25 side, and is prevented from being compressed by the returning piston 40. Accordingly, the gas pressure acting on the piston 40 does not hinder the operation of the energy absorbing mechanism, and the effect of the energy absorbing mechanism can be sufficiently exerted.

In the above pretensioner 3B,
Since the packing 48 is used, the diameter of the gas vent hole can be made larger and the escape of gas can be increased more than the narrow gas vent hole in the above-described embodiment. It is possible to perform necessary and sufficient degassing even when a large amount of gas is generated by using a gas generator having an output.

In the above-described first and second embodiments, the inclined surface 5 formed on the top of the cylinder 24 is used for positioning the rack 25 at the initial position, as shown in FIG. As shown in FIG. 1, the inner periphery of the top of the cylinder 24 is provided with a rib 5a against which the pressure receiving plate 27 contacts.
As shown in FIG. 1 (b), a projection 5b may be provided. The ribs 5a and the projections 5b are deformed or damaged when the contact force of the pressure receiving plate 27 due to the reverse rotation torque of the pinion gear 21 exceeds a specified value.
If the strength is adjusted, the mechanism can effectively function as the above-described mesh release mechanism 7. Further, in the above-described one embodiment and other embodiments, the mesh release mechanism 7 has a configuration in which both the pressure receiving plate 27 and the inclined surface 5 are deformed or broken, and the mesh between the rack 25 and the pinion gear 21 is released. However, the engagement between the rack 25 and the pinion gear 21 may be released by deformation or breakage of either the pressure receiving plate 27 or the inclined surface 5.

[0034]

According to the pretensioner of the seat belt retractor of the present invention, since the piston is provided with the gas releasing means penetrating along the moving direction of the piston for generating the viscous resistance of the gas, If the gas generated in an emergency tries to pass through the degassing means at a high speed, the viscous resistance of the gas occurs and the pressure in the cylinder does not drop in a short time, and the desired pressure can be maintained until the pretensioner operates, and However, since the pressure in the cylinder is sufficiently reduced during the time until the energy absorbing mechanism operates and during the operation, the gas pressure acting on the piston does not hinder the operation of the energy absorbing mechanism, and is sufficient for the energy absorbing mechanism. It is possible to exhibit the effect. Therefore, the piston is pressed and driven as designed by the action of the gas pressure in an emergency, and the slack of the seat belt can be reliably removed.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of one embodiment of a pretensioner according to the present invention.

FIG. 2 is a sectional view showing an initial state of a pretensioner according to one embodiment of the present invention.

FIG. 3 is an enlarged view showing a configuration of a gas release mechanism of a pretensioner according to one embodiment of the present invention.

FIG. 4 is an explanatory view illustrating the arrangement of stoppers provided in the pretensioner according to the embodiment of the present invention.

FIG. 5 is an operation explanatory view of a stopper provided in the pretensioner according to one embodiment of the present invention.

FIG. 6 is an exploded perspective view of another embodiment of the pretensioner according to the present invention.

FIG. 7 is a cross-sectional view illustrating an initial state of a pretensioner according to another embodiment of the present invention.

FIG. 8 is an enlarged view showing a configuration of a gas release mechanism of a pretensioner according to another embodiment of the present invention.

FIG. 9 is an operation explanatory view of a mesh release mechanism of a pretensioner according to another embodiment of the present invention.

FIG. 10 is an enlarged view showing the operation of a gas release mechanism of a pretensioner according to another embodiment of the present invention.

FIG. 11 is an explanatory view of another embodiment of a mechanism for positioning a rack at an initial position in the pretensioner of the present invention.

[Explanation of symbols]

 3A, 3B Pretensioner 4 Take-up shaft 5 Inclined surface 7 Mesh release mechanism 9 Stopper 10 Space 21 Pinion gear 22 Rack gear case 25 Rack 25a Rack teeth 26 Seal member 27 Pressure receiving plate 27a Small hole 27b Recess 40 Piston 41 Piston body 45, 55 Gas vent mechanism 46 First gas vent hole 46a Vertical hole 46b Horizontal hole 47 Second gas vent hole 48 Packing 48a Rack insertion hole 48b Outer peripheral portion

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-156884 (JP, A) Japanese Utility Model Application Showa 49-124731 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60R 22/46

Claims (4)

(57) [Claims] Claims 1. Gas is ignited during an emergency such as a vehicle collision.
A gas generator that generates Cylinder to which gas generated from the gas generator is guided
When, It is housed movably in the cylinder and pushed by the pressure of the gas.
A piston driven by pressure, In the event of an emergency such as a vehicle collision,
A pinion gear equipped to be able to rotate in conjunction with the take-up shaft, A piston slidably held in the cylinder has a base end
And the front end side is meshed with the pinion gear.
Mating rack teeth are provided so that the
The pinion gear is pressed and driven by the acting gas pressure.
The retractor's take-up shaft through the seat belt's slack
And a rack that rotates in a direction in which Eliminating slack of the seat belt by driving the piston
After leaving, the tension acting on the seat belt becomes more than a certain value.
Then, it is combined with an energy absorbing mechanism that reverses the winding shaft.
A seat belt retractor that is used together
In the tensioner, The piston provided at the rack base end includes a piston
Gas venting means provided along the moving direction of
A seat belt retractor
Cushion. 2. A pretensioner for a seat belt retractor according to claim 1, wherein said degassing means has an elongated narrow tube-shaped portion extending a predetermined length in a moving direction of said piston. 3. The diameter of the thin tube-shaped portion is 0.6 to 1.
The pretensioner according to claim 2, wherein the pretensioner is 2 mm. 4. The pretensioner for a seat belt retractor according to claim 1, wherein said degassing means has a thin tube formed in said piston.