DE9321433U1 - Belt tensioners for seat belt arrangements in motor vehicles - Google Patents

Description

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Vehicle Safety Technology GmbH ■ .;.. :

Belt tensioners for seat belt arrangements in motor vehicles

The invention relates to a belt tensioner for safety belt arrangements in motor vehicles with a belt winding mechanism attached to the vehicle chassis, preferably provided with a return spring arrangement and acceleration locking device, a drive for the belt winding mechanism that works in the belt winding direction and an acceleration sensor that responds to accelerations occurring in an accident and is in triggering connection with the drive, such that when an accident acceleration occurs, the drive is triggered and the belt winding mechanism thereby suddenly rolls up the belt by a predetermined distance that is sufficient to firmly fasten the belt to the occupant it is holding.

Since the retraction force of a belt retractor equipped with a retraction spring is very low for reasons of comfort and is generally only between 2 and 22 N, seat belts worn by the occupants of a vehicle generally only fit relatively loosely on their bodies. If the occupant is also wearing bulky clothing, such as a thick coat, it is no longer guaranteed that the seat belt will fit sufficiently tightly against the user's body in the event of an accident. For this reason, there is a need to tighten the belt when putting it on.

If an accident occurs, the belt system should suddenly tighten so that the occupant is held securely in place by the belt system without any great play.

Belt tensioners are therefore required that tighten the belt with a high force over a sufficient distance. At the same time, however, they should be compact and inexpensive and be detachable after tightening due to an accident, so that the belt can still be fastened after a minor accident, for example, to drive the car to a workshop.

It is already known (DE-OS 42 21 398) to use a tensioning device to suddenly move the belt buckle attached to the chassis a certain distance towards the vehicle chassis in the event of an accident, in order to shorten the belt as required for the seat belt to fit snugly against the occupant's body. Belt tensioners are also already known, which usually use pyrotechnic propellant charges to rotate the belt reel to tighten the belt. However, the known tensioners have the particular disadvantage of either only tightening over a short distance (EP-O 059 643 Bl, DE-25 05 626 Al, US-A-24 Jl 907) or they are not sufficiently compact (DE 35 31 856 Al).

The present invention aims to use a belt retractor mechanism in safety belt arrangements to tighten the belt by the required amount in the event of dangerous and accident-related accelerations on the vehicle before the occupant begins to move due to the accident acceleration. The main problem here is that when pressure suddenly builds up, the drive of the belt retractor mechanism can generally only complete one revolution if the tensioner arrangement is compact, which in many cases is not sufficient to tighten the safety belt sufficiently. The invention aims to remedy this. Furthermore, the retraction spring arrangement should still be usable after the tensioner has been triggered due to an accident. Finally, the belt tensioner should be compact.

To solve this problem, the invention provides that the drive has:

— one when the acceleration sensor responds

triggerable pressure source, in particular pyrotechnic charge, which when triggered in a pressure chamber suddenly builds up a high pressure,

- a pressure chamber which is connected or connectable at its beginning to the pressure chamber and is at least approximately pressure-tight

closed, essentially part-circular running space, in which a force-transmitting sealing means, which divides the running space in the circumferential direction into two pressure-tight, separate spaces, one of which is connected to the pressure space in terms of pressure, is or can be arranged, which at the latest immediately after the triggering

- is movable over at least part, preferably over the largest part of the part-circular circumference of the running space,

- radially inside with a hub that is rotationally coupled to the belt retractor mechanism or can be rotationally coupled immediately after the triggering center at the latest, and

- engages radially on the outside with a circumferentially fixed, part-circular inner wall and

- is arranged close to the pressure chamber before activation and, when pressure occurs in the pressure chamber after activation of the pressure source, moves along the fixed inner wall and rotates the central hub, which is non-rotatably coupled to the belt retractor mechanism, through the running chamber over a considerable distance, whereby

- the axial end faces of the hub sealing means and the inner wall are in sealing engagement with walls fixed to the housing, one of which is preferably a removable cover.

The idea behind the invention is that the hub is rotated by an angle that is determined by the ratio of the inner wall diameter to the hub diameter, in such a way that the belt is tightened by a distance that is longer than the product of the diameter of the belt roller and the angle of passage (in radians, rad).

An advantageous embodiment of the invention provides that the part of the running chamber facing away from the pressure chamber is provided with a vent at or near its end. This allows the air present in front of the force-transmitting sealing means to escape as it circulates around the hub, so that no excessive pressure builds up in the space in front of the force-transmitting sealing means, and thus a higher pulling force and a longer running distance can be achieved or a smaller propellant can be used.

While it is basically possible to keep the force-transmitting sealant permanently in engagement with the hub, however, this would impair the normal belt tensioner function.

is impaired, it is preferred if the force-transmitting sealing means is initially disengaged from the inner wall and/or the hub, preferably the hub, or this with the belt winding mechanism, and only when the pressure source is triggered does the force-transmitting sealing means engage with the inner wall and/or the hub or the hub with the belt winding mechanism, and before the pressure build-up in the running space in front of the force-transmitting sealing means is so great that the force-transmitting sealing means is moved on its path around the axis of the hub.

In order to achieve a particularly compact and simple embodiment of the present invention, it may be advantageous to arrange the hub and the belt roller coaxially.

To simplify the device according to the invention, the hub and possibly also the force-transmitting means can be mounted in a housing attached to the chassis in a rotatable but immovable manner.

A further advantageous embodiment of the invention provides for the partially circular inner wall and preferably also the force-transmitting sealing means and, if necessary, other parts of the tensioner, such as additional sealing means, to be arranged on a slide in such a way that the engagement between the force-transmitting sealing means and

the inner wall or the hub or the hub and the belt retractor mechanism is only created when an accident-related acceleration occurs and the pressure source is thereby triggered.

According to an embodiment of the invention, this slide can be moved into its working position by a valve displacement member.

In a practical embodiment of the invention, a planetary gear is used in which the force-transmitting sealant is designed as a planetary gear, the inner wall as an internal gear ring and the hub as a sun gear, whereby the transmission properties of a planetary gear are used to bring about a rotation of the sun gear with a significantly greater angle from a rotation of the planetary gear that is slightly less than 360°. If the rotation of the planetary gear is, for example, 310", which is possible taking into account the required pressure seal at the end of the planetary gear running space, then a rotation angle of the sun gear of 650" can be achieved with a suitable selection of the diameter of the sun gear and planetary gear. While the absolute rotation path of the center of the planetary gear is, for example, 10 cm, tightening the seat belt by, for example, 2 2 cm, i.e. more than twice the movement path of the

planetary gear.

In the version with planetary gear, the
Sun gear in normal operation under the influence of the return spring normally provided or the force applied by the occupant on the
Tensile forces exerted by the belt within the limits given by the belt retractor mechanism unhindered in both directions
Only when an accident-related acceleration
occurs and the pressure source is triggered, the
Internal gear ring, the planetary gear and the one with a
The sun gear provided with external teeth engages, and the sudden belt tensioning according to the invention is now
carried out.

So that after triggering the sudden
Belt tensioning function of the normal belt retractor mechanism
is still functional, the planetary gear design provides that the planetary gear running space has an extension at the beginning and/or at the end where the planetary gear comes out of engagement with the sun gear and/or the internal gear ring. If the planetary gear remains between
beginning and end of its orbit, so during normal operation of the belt retractor mechanism it will be in one
or other direction until it reaches the beginning or end
of his career. There it then comes out of action
with at least one of the surrounding gears, whereby

the function of the normal belt retractor mechanism is not hindered by the planetary gear hitting one of the ends of its orbit. Preferably, the inner gear ring should not be continued in the area of the extension.

In the version of the tensioner equipped with a planetary gear, the engagement of the planetary gear in the gearing assigned to it can also be brought about by the planetary gear being moved from a rest position, for example a locked position, by the pressure built up in the pressure chamber into a working position in which it is in engagement with the sun gear and the internal gear ring when the pressure source is triggered.

A further alternative embodiment of the device according to the invention provided with the planetary gear is characterized in that an internal gear segment is arranged at the beginning of the internal gear ring so as to be radially displaceable and can be displaced by the pressure in the pressure chamber from a rest position, where it is not engaged with the planetary gear, into a working position, where it is in engagement with the planetary gear and also brings it into engagement with the sun gear if necessary.

In another preferred practical embodiment of the invention, a with its one end at the hub

A band that is attached and tightly wound around the hub and connected to the inner wall at its other end is unrolled along the inner wall by the application of pressure, whereby the hub is rotated by the unwinding movement.

In a preferred embodiment of the tensioner arrangement provided with a band as a force-transmitting means, an additional sealing means is provided next to the band in order to obtain an improved seal of the pressure chamber by an enlargement of the sealing surface on the end faces.

In the version with a belt as a force-transmitting means, it can be provided that an intervention only takes place after the occurrence of an accident acceleration via a rotary coupling, as described, for example, in DE-A-43 20 854.

A particular advantage of both designs is that the travel increase is achieved with a very compact design that is adapted to the shape of the belt retractor mechanism.

In order to achieve the pulling force required for the sudden tightening of the belt, for example 1250 N, a significantly greater force of e.g. 2500 N must be generated on the force-transmitting sealing means, i.e. on the belt or on the planetary gear, which can be achieved by means of a pyrotechnic

However, charging is easily possible.

The invention is described below by way of example with reference to the drawing, in which

Fig. 1 is a schematic, partially sectioned and exploded, perspective view of a belt tensioner according to the invention,

Fig. 2 is a view of the object of Fig. 1 in the direction of arrow II in a non-exploded representation,

Fig. 3 is an enlarged, cutaway, perspective view of the drive of the belt tensioner according to Figs. 1 and 2, with the drive being seen from the opposite side as shown in Fig. 1.

Fig. 4 is a partial view of the object of Fig. 3 immediately after the pressure source has been activated,

Fig. 5 is a view similar to Fig. 3 in a position immediately at the beginning of the pressurization of the planetary gear, also illustrating the position of the planetary gear at the end of its path,

Fig. 6 a section of another embodiment in the area of the beginning of the planetary gear running rough, -,

Fig. 7 is a view similar to Fig. 6 of another embodiment,

Fig. 8 is a partial view of another embodiment of the drive of a belt tensioner according to the invention,

Fig. 9 is a partial perspective view of another embodiment of the drive of a belt tensioner according to the invention with the cover removed in a position as it is assumed immediately after the start of the pressure application, and

Fig.10 is a partial perspective view of a further development of the embodiment according to Fig. 9.

Figures 1 to 8 describe the inventive design of a belt tensioner with a planetary gear.

According to Figures 1 and 2, a belt retractor mechanism is attached to the chassis 11 of a motor vehicle by means of a bracket 30. The belt retractor mechanism 12 has a belt reel 25, onto which the belt is wound by means of a

A safety belt 16 can be wound up by means of a coil spring arrangement 31 arranged in the holder 30 so that it comes into contact with the body of an occupant who has fastened the safety belt 16 with a tensile force of between 2 and 22 N.

On the end face facing away from the spiral spring arrangement 31, the belt retractor mechanism 12 has a sun gear 21 provided with external teeth, which engages axially in a housing 24 of a drive 13 closed off by two flat end walls 4. For the sake of clarity, the sun gear 21 in Fig. 1 is shown not only in its position within the housing 24 but also in its coaxial arrangement on the belt reel 25 - i.e. twice.

In the rest position illustrated in Figs. 1 and 2, the sun gear 21 can rotate freely within the housing 24, so that the belt retractor mechanism 12 can perform its normal retraction or extension function.

An acceleration sensor 14, indicated in Fig. 1, is attached to a suitable location in the vehicle and is connected via a control line 15 to a pressure source 17 arranged in the housing 24, which is expediently implemented by a pyrotechnic charge which, when an accident-related acceleration signal occurs at the output of the

· * M

- 14

acceleration sensor 14 is ignited.

According to Fig. 3, a substantially cuboid-shaped slide receiving space 3 2 is provided within the housing 24 attached to the holder 3 0 (Fig. 1, 2), within which a slide 2 6 is arranged that can be moved up and down over a limited path 3 3. The slide 26 can be moved into its upper position shown in Fig. 1 and 3 by a spring 3 4, where it rests against a projection 35 of the housing 24.

The cuboid-shaped slide 2 6 has a planetary gear running space 19 which eccentrically surrounds the sun gear 21 arranged in it and which is limited on its radial outer circumference by an internal gear ring 2 2 provided on the slide 2 6. At the top, the planetary gear running space 19 passes over a channel 3 6 into a receiving space 37 of the housing 24.

Starting from the lower end of the channel 36, the planetary gear running space 19 extends around the sun gear 21 by approximately 310°. At the end of the planetary gear running space 19, a slide-mounted, radially inwardly directed pressure sealing projection 38 is provided, which, however, in the position according to Fig. 1, has a distance A from the circumference of the sun gear 21 in accordance with the eccentricity. Above the slide 26, a pressure chamber 18 is provided in the housing 24, at the

•"••j.

left end, the pyrotechnic charge 17 is arranged as a pressure source. At the end of the pressure chamber 18 opposite the pyrotechnic charge 17, a valve displacement member 27 is arranged, which is connected to the housing 24 by means of shear pins 39 and is designed as a wedge, which is located in contact with a wedge-shaped constriction 40 at the end of the pressure chamber 18. The constriction 40 merges into the receiving chamber 37. The channel 3 6 borders on the end of the valve displacement member 27 facing away from the pyrotechnic charge 17.

At the end of the planetary gear running space 19, vent holes 23 are provided in the wall of the slide 2 6 and the housing 2 4 .

At the beginning and end, the planetary gear running space 19 has extensions 28 and 29, respectively, through which the planetary gear running space 19 is extended in these areas so that a planetary gear 20 arranged in the planetary gear running space 19 is there out of engagement with the sun gear 21 or the internal gear ring 22.

The planetary gear 20 is rotatably attached to the slide 26 according to Fig. 3 and is in engagement with the beginning of the internal gear ring 22. The planetary gear 20 is at a distance B from the external teeth of the sun gear 21, which is e.g.

can be 1 mm.

The housing 24 is closed at both ends by a cover 44, which is only indicated in Fig. 2, so that the chambers 18, 36, 37 are pressure-tightly sealed to the outside.

The function of the described drive 13 is as follows:

As soon as the acceleration sensor 14 according to Fig. 1 sends an accident-related acceleration signal to the pyrotechnic charge 17 via the control line 15, the latter ignites and generates a high explosion pressure in the pressure chamber 18. This simultaneously forces the slide 26 downwards and the valve displacement member 27 to the right in Fig. 1. Due to the high pressure, the shear pins 39 are sheared off and the valve displacement member moves to the right, as is indicated in Fig. 4. At the same time, the slide 26 moves downwards against the force of the spring 34 due to the direct pressure effect and the wedge effect of the valve displacement member 27, whereby the internal gear ring 22 becomes concentric with the sun gear 21 and the planetary gear 20 engages with the sun gear 21. Up to now, the planetary gear 20 is still free of the explosion pressure, so that switching takes place without load. Only then does the valve displacement member 27 reach the position shown in Fig. 5, in which the pressure chamber 18 is now supplied via the channel

- 17 -

3 6 is connected to the beginning of the planetary gear running space 19. The explosion pressure can now act on the planetary gear 20, which meshes with both the internal gear ring 2 2 and the sun gear 21, and move it anti-clockwise on an orbit around the axis of the sun gear 21. By moving the slide 26 from the position in Fig. 3 to the position in Fig., the distance A between the pressure sealing projection 38 and the circumference of the sun gear 21 is also reduced to a minimum, so that the pressure in the pressure chamber 18 is prevented by the pressure sealing projection 3 8 from entering the planetary gear running space 19 directly. The planetary gear 2 0 now rolls on the internal gear ring 2 2 and drives the sun gear 21 in the direction of the arrow to rotate. Due to the planetary gear ratio, the sun gear 21 rotates significantly faster than the planetary gear 20 rotates around its axis.

As soon as the belt 16 is tight against the body of the occupant, the movement of the planetary gear 20 on its orbit ends. The normal locking mechanism of the belt retractor mechanism 12, not shown in the drawings, now comes into operation, which prevents the seat belt 16 from being pulled out when the vehicle accelerates.

As soon as the pressure in the pressure chamber 18 has subsided, the belt retractor mechanism 12 can be operated in the usual way, whereby the planetary gear rolls freely between the sun gear 21 and the inner gear ring 22. At the ends of the planetary gear running chamber 19, the planetary gear 20 reaches the area of the extensions 28 or 29, where it comes out of engagement with at least one of the gears, so that the sun gear 21 remains freely rotatable even in these positions of the planetary gear 20 and the normal function of the belt retractor mechanism 12 is not hindered. In Fig. 5, the planetary gear 20 is shown firstly in its position at the beginning of its orbit and a second time at 20' at the end of the orbit 20.

In the following figures, the same reference numbers designate corresponding components as in Figs. 1 to 5.

In the embodiment according to Fig. 6, no slider 26 is provided; rather, both the sun gear 21 and the internal gear ring 22 on the housing 24 are arranged concentrically to one another from the outset. In addition, the pressure sealing projection 38 is always located at a sealing minimum distance from the outer circumference of the sun gear 21.

Furthermore, in the embodiment according to Fig. 6, the valve sliding member 27 is omitted. Instead, the planetary gear

20 is housed in the rest position in a locking recess 41 at the beginning of the planetary gear track 19. The locking recess 41 is connected to the pressure chamber 18 via the channel 3 6. When arranged within the receiving chamber 41, the planetary gear 20 is not engaged with the sun gear

If pressure is built up in the pressure chamber 18, the planetary gear 20 is pressed out of the locking recess 41 into engagement with the sun gear 21 and the internal gear ring 22, whereupon the function described above with reference to Figs. 1 to 5 takes place.

Fig. 7 also shows an embodiment in which the sun gear 21 and the internal gear ring 22 are arranged concentrically to one another on the housing 24 from the outset. In this case, the pressure in the pressure chamber 18 acts on a radially displaceable internal gear ring segment 22' provided at the beginning of the planetary gear running chamber 19, which has a valve projection 42 which initially keeps the pressure in the pressure chamber 18 away from the beginning of the planetary gear running chamber 19.

In the event of ignition of the charge 17, the inner gear ring segment 22' is first moved essentially radially towards the sun gear 21, whereby the planetary gear 20 held on the inner gear segment engages with the sun gear

- 20 -

21. At the same time, the internal gear segment 22' comes into peripheral alignment with the fixed internal gear ring 22. Since the valve member 42 also releases a U-shaped pressure channel 43 with the radial inward displacement of the internal gear ring segment 22', the pressure prevailing in the pressure chamber 18 can now be passed on again through the channel 3 6 to the planetary gear 2 0 which is in engagement with the teeth of the internal gear ring 2 2 and the sun gear 21.

Fig. 8 shows a similar embodiment, but the pyrotechnic charge 17 is arranged above the toothed segment 22' and the planetary gear 20 is held in the rest position, e.g. by magnetic means or formation on the inner toothed segment 22' (not shown).

A further embodiment is shown in Fig. 9, which only shows the essential part of the belt tensioner. The belt tensioner has a band 20a in a housing 24 as a force-transmitting sealing means, which extends over the width of the spaces 18, 19 and which is fastened with one end to a fastening point 47 on the hub 21a, is wound onto it in such a way that when the band 20a is pulled off, the hub 21a rotates in the belt winding direction and from its outer end of the wound part of the hub 21a in a channel

36 is guided in a 180° bend to the smooth inner wall 22a, against which it is then guided to a fastening point 48 at the beginning of the running space 19 next to the channel 3 6, where its other end is fastened.

The housing 24 is closed similarly to Fig. 2 with two flat end walls 44, one of which is designed as a screw-on cover shown in removed form, and against which the edges of the band 20a rest from the inside, so that in front of the 180" bend the part which is closed off to the outside in a pressure-tight manner and is connected to the pressure chamber 18 is formed, and behind the 180" bend the ventilated part of the running chamber 19 is formed.

Normally, a clutch 46, indicated only in dashed lines, is provided between the belt 20a and a drive shaft 49 which projects axially from the hub 21a and is thought to be coupled to the belt reel 25 in a rotationally fixed manner. This clutch is normally disengaged and is engaged in a manner not shown in the event of accident-related acceleration. However, the clutch could also be provided between the drive shaft 49 and the belt reel 25.

The design shown in Figure 10 has an additional sealing cylinder 45 in the 18 0' bend of the band 20a, the flat end faces of which are in sliding sealing contact with the walls 44.

This results in a better frontal sealing of the two parts of the running space 19.

In both cases, the coupling can be designed in such a way that the intervention is released a sufficient time after the accident-related tightening.

The effect of the embodiments shown in Fig. 9 and 10 is as follows:

In the initial position, the band 20a is wound onto the hub 21a to the maximum and the 180° bend is located close to and opposite the channel 36. In this way, the pressure chamber 18 between the band 20a, the pressure-sealing projection 38, the inner wall 22a and the end walls 44, which can be acted upon by the channel 36, has its minimum volume.

However, in the initial position it is also possible that the band 20a does not yet have a 180" bend, but is guided essentially in a straight line from the hub 21a to the inner wall at or close to the fastening point 48.

If an accident-related acceleration then occurs, the pressure source 17 is triggered and the clutch 4 6 between the belt 20a and the belt retractor mechanism 12 is engaged.

The propellant gases formed by the pyrotechnic charge 17 flow through the channel 36 into the pressure chamber 18, so that the pressure here is greater than in the part of the chamber facing away from the pressure source. This pressure difference causes a force directed in the circumferential direction away from the channel 36 on the 180° arc of the band 20a, whereby, since the band 20a is held at the fastening point 48 on the housing, a torque is exerted on the hub 21a in an anti-clockwise direction and the hub 21a is driven into a corresponding rotary movement. During this rotational movement of the hub 21a, the belt reel 25 is rotated in the belt-tightening direction via the clutch 46 and at the same time the belt wound onto the hub and held at its other end at the fastening point 48 unwinds, whereby under the influence of the pressure difference the belt 20a in the part-circular running space 19 clings to the inner wall 22a over a distance that increases during this process, starting from the fastening point 48. The 180" arc runs through the running space 19 in an anti-clockwise direction.

Figures 9 and 10 show the belt tensioner shortly after the start of the pressurization, where the 180" arc has only passed through a small part of the running space.

In case the band 2 0a is in the initial position

- 24 -

straight from the hub 21a to the inner wall 2 2a near the
Fastening point 48 is guided, will at the beginning of the pressure application under unwinding rotation of the hub
First form the 180" arc and then move through the running space 19 as described above.

The sealing cylinder 4 5 naccording to Fig. 10 leads, while the
Movement of the 18 0° arc through the running space 19 a
Rolling movement on the band part that is pressed against the inner wall 22a. In this case, the pressure force is transferred to the 180" sheet via the sealing cylinder 45.

The distance by which the band 2 0a is unwound,
corresponds essentially to the product of the running angle of the apex of the 18 0" arc (in rad) and the inner wall diameter. The angle of rotation by which the hub 21a can be rotated
is the ratio of this size to the hub diameter. This increases the angle of rotation of the hub by the ratio of the inner wall diameter to the hub diameter.

- 25 -

List of reference symbols

11 Vehicle chassis

12 Belt retractor mechanism

13 Drive working in belt retraction direction

14 Acceleration sensor

15 Release connection

16 Belt

17 Pressure source

18 Printing room

19 Partially circular running space

2 0 power-transmitting, sealing planetary gear

20' power-transmitting, sealing planetary gear in second position

20 a force-transmitting sealing band

21 Sun gear
21a central hub

22 Partially circular internal gear 22' Internal gear segment

22a Partially circular inner wall

2 3 ventilation openings

24 Housing

25 Belt reel

26 sliders

27 Valve sliding element 2 8 Extension

29 Extension

3 0 Bracket

31 Return spring arrangement

3 2 Slider accommodation space

3 3 limited path

34 Spring

3 5 lead

3 6 Channel

3 7 Recording room

3 8 Pressure sealing projection 39 Shear pins

4 0 Constriction

41 Recording room

42 Valve projection

4 3 U-shaped pressure channel

4 4 Lid

45 Sealing body

46 Clutch

47 Hub-side fastening point of the belt end

48 fastening point of the strap end on the housing side

49 Drive shaft

Claims (8)

·: I PROTECTION CLAIMS 1. Belt tensioner for safety belt arrangements in motor vehicles with a belt retractor mechanism attached to the vehicle chassis (11), a drive (13) for the belt retractor mechanism operating in the belt retraction direction and an acceleration sensor (14) which responds to accelerations occurring in an accident and is in trigger connection (15) with the drive (13) in such a way that when an accident acceleration occurs, the drive (13) is triggered and the belt retractor mechanism (12) thereby suddenly retracts the belt (IS) by a predetermined distance which is sufficient to firmly attach the belt (16) to the occupant held by it,
characterized in that the drive (13) has a pressure source (17) which can be triggered when the acceleration sensor (14) responds and which, when triggered, suddenly builds up a high pressure in a pressure chamber (18), a substantially partially circular running chamber (19) which is connected or connectable to the pressure chamber (18) at its beginning and is at least approximately pressure-tight, in which a force-transmitting sealing means (20a, - 20a, 45) is arranged or can be arranged, which divides the running chamber (19) in the circumferential direction into two pressure-tight, separate chambers, one of which is connected to the pressure chamber (18) in terms of pressure, and which at the latest immediately after the triggering ''&Agr;&igr;- 1 1 OV" is movable over at least part of the partially circular circumference of the running space (19), radially inwardly with a central hub (21; 21a) which is coupled to the belt retractor mechanism (12) in a rotationally fixed manner or can be coupled in a rotationally fixed manner immediately after release at the latest, and radially outwardly in engagement with a circumferentially fixed, part-circular inner wall (22a)
stands and is arranged close to the pressure chamber (18) before triggering and when pressure occurs in the pressure chamber (18)
after triggering the pressure source (17) under movement
along the fixed inner wall (22a) and rotation of the central hub (21a) which is coupled to the belt retractor mechanism (12) in a rotationally fixed manner, the running space (19) by
runs through a considerable distance, whereby the axial end faces of the force-transmitting sealing means (20a; 20a, 45) of the hub (21a) and the inner wall (22; 22a) are in sealing engagement with the housing-fixed walls (44), and that the force-transmitting sealant is a
its width extending over the running space (19)
Band (2 0a) which is fastened at one end to a point (47) on the hub (21a), is wound onto the hub (21a) in such a way that when unwound the hub rotates in the belt winding direction, then, depending on the rotational position of the hub (21a), in a straight line
and/or more or less curved and/or in an 18 0° arc to the inner wall (22a), on this at the latest after a certain rotation of the hub (21a) it rests a little in the direction of a pressure channel (3S) and is attached with its other end to a fastening point (48) of the housing (24). 2. Belt tensioner according to claim 1, characterized in that the part of the running chamber (19) facing away from the pressure chamber (18) is provided with a vent (23) at or near its end. 3. Belt tensioner according to one of the preceding claims, characterized in that the force-transmitting sealing means (20; 20a, - 20a, 45) is initially disengaged from the part-circular inner wall (22a) and/or the hub (21a), or the hub (21a) is disengaged from the belt retractor mechanism (12), and only when the accident acceleration occurs immediately before, simultaneously with or in particular by the triggering of the pressure source (17) is this engagement established, and in fact before the pressure build-up in the running space (19) in front of the force-transmitting sealing means (20a; 20a, 45) is so great that the force-transmitting sealing means (20a; 20a, 45) is moved by a considerable distance on its orbit around the axis of the hub (21a). 4. Belt tensioner according to one of the preceding claims, characterized in that the hub (21; 21a) is coaxial with a belt reel of the belt retractor mechanism (12). - 30 - 5. Belt tensioner according to one of claims 1 to 4, characterized in that 'the hub (21; 21a) is arranged rotatably but immovably in a housing (24) fastened to the chassis (12). 6. Belt tensioner according to claim 1, characterized in that a sealing cylinder (45) is arranged in the 180° arc, the flat end faces of which are in sliding sealing engagement with the walls (44). 7. Belt tensioner according to claim 1 or 6, characterized in that between one end of the belt (20a) and the belt retractor mechanism (12) there is a normally disengaged clutch (46) which is only engaged in the event of an accident-related acceleration. 8. Belt tensioner according to claim 1, characterized in that an additional sealing means is provided next to the band (20a) in order to obtain an improved seal of the pressure chamber by enlarging the sealing surface on the end faces.