Belt retractor with reversible belt tensioner

Abstract

The invention relates to a belt retractor (1) having a belt shaft (3), which is rotatably mounted in a frame (2), which can be securely fixed to a vehicle and on which a seat belt can be wound at one end, and a reversible belt tensioner (4), which is rotatably mounted in the frame (2), the invention relates to a reversible belt tensioner (1) which, when activated to tension a seat belt, drives a belt shaft (3) in a winding direction via a tensioner drive wheel (5) around the belt shaft (3), and a torque limiter which is arranged between the tensioner drive wheel (5) and the belt shaft (3), the invention relates to a torque limiter for limiting a torque that can be transmitted between a tensioner drive wheel (5) and a belt shaft (3), the torque limiter being formed by a dimensionally stable ring (6), the ring is connected in a form-fitting manner to the tensioner drive wheel (5) or to a component connected in a rotationally fixed manner to the tensioner drive wheel in the direction of the torque to be transmitted by means of a radially outwardly directed first locking geometry (7), wherein the dimensionally stable ring (6) is connected in a form-fitting manner to the belt shaft (3) or to a component connected in a rotationally fixed manner to the belt shaft (3) by means of a second radially inwardly directed locking geometry (9) in the direction of the torque to be transmitted.

Description

[0001] The present invention relates to a seat belt retractor having a reversible seat belt pretensioner, the seat belt retractor having the preamble features as claimed in claim 1.

[0002] A seat belt retractor having a reversible seat belt pretensioner is used in motor vehicles and has the task of increasing the seat belt force and eliminating any slack in the seat belt system in the pre-accident phase, so that in a subsequent accident the seat belt is as close as possible to the occupant and the occupant is associated with the deceleration of the vehicle as early as possible. If no accident occurs after the initial phase, the seat belt force decreases and the seat belt retractor can fully perform its intended function again. A small electric motor has proven to be a preferred drive device for the reversible seat belt pretensioner, the rotational speed of which is transmitted via a transmission to the seat belt shaft of the seat belt retractor. To ensure that the seat belt retractor is not disturbed by the reversible seat belt pretensioner during normal operation, a coupling mechanism must also be provided, by means of which a connection is established between the seat belt pretensioner and the seat belt shaft of the seat belt retractor only when the reversible seat belt pretensioner is activated.

[0003] Accidents are classified into different categories according to the relative speed and type of the obstacle. One accident category is the so-called "low-speed collision" or AZT collision (Allianz Technology Center collision test), in which the vehicle hits a relatively hard obstacle at a relatively low speed. During this test, irreversible restraint devices such as airbags or irreversible seat belt pretensioners must not be triggered. On the other hand, reversible restraint devices such as reversible seat belt pretensioners can or should be triggered.

[0004] The disadvantage of using a reversible seat belt pretensioner is that when activated in a low-speed collision such as an AZT collision, they apply an undesired high seat belt force of up to 3 kN to the occupant during the subsequent forward movement of the occupant until the seat belt retractor is locked due to the connection created between the reversible seat belt pretensioner and the seat belt shaft.

[0005] A seat belt retractor having a reversible seat belt pretensioner is known from EP 1504971 B1, in which the coupling mechanism between the seat belt shaft and the reversible seat belt pretensioner has means for limiting the torque to be transmitted. The means are formed by teeth associated with the seat belt shaft and teeth associated with the seat belt pretensioner, the teeth being engaged to transmit the torque from the seat belt pretensioner to the seat belt shaft and the teeth disengaging when the torque exceeds a set value. The set torque value at which the teeth disengage is determined by a helical spring that preloads the teeth in the engagement direction.

[0006] The disadvantage of this solution is that the torque limiting mechanism requires a relatively large installation space and is expensive due to many individual components.

[0007] Another seat belt retractor is known from document DE 10 2005 001 709 A1, in which a torque limiter is provided between the reversible seat belt tensioner and the seat belt shaft, which automatically decouples the reversible seat belt tensioner from the seat belt shaft when a torque acts, which torque causes an increase in the force limiting level of a subsequently activated force limiting device. The torque limiter is realized in the form of an elastically deformable metal strip, which is designed as an open dimensionally stable ring with a locking geometry in the form of radially outwardly directed teeth, which ring is hooked at one end via a hook to a pawl bracket assigned to the seat belt shaft.

[0008] Furthermore, a seat belt retractor with a device for limiting torque is known from document DE 10 2008 060 208 B4, which device is formed by a metal plate with radially outwardly formed features in the form of laterally open teeth, and the support structure is formed by undeformed areas between the teeth and in the edge regions of the teeth.

[0009] Against this background, the object of the present invention is to create a seat belt retractor with a reversible seat belt tensioner of the type described at the beginning, in which the device for limiting the torque between the reversible seat belt tensioner and the seat belt shaft of the seat belt retractor is realized using the most cost-effective device possible and limits the torque with increased reliability.

[0010] This object is achieved by a seat belt tensioner with a reversible seat belt tensioner having the features of claim 1. Further preferred embodiments of the invention can be found in the dependent claims.

[0011] The basic idea of the invention is that the dimensionally stable ring is positively connected in the direction of the torque to be transmitted to the seat belt shaft or to a component connected to the seat belt shaft in a rotationally fixed manner by means of a second radially inwardly directed locking geometry.

[0012] The advantage of the proposed solution is that the torque limiter is connected to the tensioner drive wheel not only via the first locking geometry in the direction of the torque to be transmitted, but also to the seat belt shaft via the second locking geometry. This makes it unnecessary to have additional fastening of the torque limiter, for example, in the case of a hook-based solution with a hook known from DE 10 2005 001 709 A1. Thus, the torque limiter is directly or indirectly connected to the tensioner drive wheel and, in an active manner, directly or indirectly connected to the seat belt shaft. In addition, the maximum transmissible torque can be defined not only by the design of the first locking geometry and the resulting positive connection, but also by the design of the second locking geometry and the resulting positive connection and configured. Another advantage of the proposed solution is that the assembly of the seat belt retractor is simplified because the torque limiter specifies the alignment of the torque limiter by means of an additionally provided second locking geometry and thus specifies the alignment of the tensioner drive wheel or the component connected to the tensioner drive wheel in a rotationally fixed manner with the seat belt shaft or the component connected to the seat belt shaft in a rotationally fixed manner. If an additional clutch is provided between the tensioner drive wheel and the seat belt shaft, the proposed solution can be used to fix the tensioner drive wheel and the seat belt shaft or the component connected to it in a rotationally fixed manner in the optimal alignment for the clutch process. The torque limiter is designed in the form of a dimensionally stable ring, which is dimensionally stable in that it retains its shape with the first locking geometry and the second locking geometry until the maximum torque to be transmitted is reached, but can still perform small spring movements which, when the maximum torque to be transmitted is exceeded, result in the cancellation of the positive connection produced via the first locking geometry and / or the second locking geometry.

[0013] Furthermore, it is proposed that the first locking geometry is formed by a plurality of protrusions spaced apart from one another and pointing radially outwards. The advantage of the proposed design of the first locking geometry is that it is particularly easy to manufacture. If the torque limiter is implemented as a metal ring, the protrusions can be formed, for example, by a stamping process. If the torque limiter is implemented as a dimensionally stable plastic ring, the protrusions can be formed during the production of the plastic ring, for example, in an injection molding process.

[0014] Furthermore, it is proposed that the protrusions of the first locking geometry are each formed by a tip having two sides converging towards one another at an acute angle. Due to the proposed shape of the first locking geometry, the spring characteristics of the dimensionally stable ring are particularly achieved in the region of the protrusions of the first locking geometry and the adjacent spring sections of the ring. In addition, the protrusions formed in this way enable a very good positive connection between the torque limiter and the tensioner drive wheel or the component connected to the tensioner drive wheel in a rotationally fixed manner.

[0015] Furthermore, it is proposed that the second locking geometry is formed by a plurality of protrusions that are spaced apart from each other and point radially inwards. The resulting advantages are the same as those of the radially outwards pointing protrusions of the first locking geometry.

[0016] Furthermore, it is proposed that in this case, the protrusions of the second locking geometry have a partially circular cross-section. Due to the partially circular design of the protrusions of the second locking geometry, during the compression movement of the loop in the region of the first locking geometry, these protrusions each form a kind of local pivot bearing for the loop.

[0017] Furthermore, it is proposed that the protrusions of the second locking geometry are arranged between the protrusions of the first locking geometry with respect to the direction of rotation of the tensioner drive wheel. Due to the proposed arrangement of the protrusions of the second locking geometry, the protrusions of the first locking geometry are supported on both sides during the compression movement by the protrusions of the second locking geometry, which are supported on the seat belt shaft or on a component that is rotationally fixed to the seat belt shaft.

[0018] Furthermore, it is proposed that the number of protrusions of the first locking geometry is even and the number of protrusions of the second locking geometry is odd, or vice versa. Thus, the loop is shaped in such a way that the first and second protrusions are regularly arranged at the same distance from each other, and only one of the protrusions is omitted to achieve an open loop, while creating a gap. The loop is always supported in its end region by two protrusions of the first locking geometry on its outer side or by two protrusions on its inner side.

[0019] Furthermore, it is proposed that the number of protrusions of the first locking geometry is less than the number of protrusions of the second locking geometry. The number of protrusions of the second locking geometry is deliberately chosen to be greater than the number of protrusions of the first locking geometry, so that the loop is fixed to the seat belt shaft more evenly and more firmly than to the tensioner drive wheel.

[0020] Furthermore, it is proposed that the dimensionally stable ring is open and, in the case of applying a spring preload, abuts against the seat belt shaft or against a component connected to the seat belt shaft in a rotationally fixed manner, or, in the case of applying a spring preload, abuts against the pretensioner drive wheel or against a component connected to the pretensioner drive wheel in a rotationally fixed manner. The dimensionally stable ring is dimensioned in such a way that, using its elastic properties, the ring is expanded or compressed in order to be mounted on the seat belt shaft or the pretensioner drive wheel or on a component connected to the seat belt shaft or the pretensioner drive wheel in a rotationally fixed manner, and is then inserted or placed. After the insertion or placement, the ring returns to its original shape and is then automatically fixed in place by applying a spring tension after being mounted on the seat belt shaft, the pretensioner drive wheel or on a component connected to it in a rotationally fixed manner.

[0021] Furthermore, it is proposed that the dimensionally stable ring is supported on the pretensioner drive wheel or on a component connected to the pretensioner drive wheel in a rotationally fixed manner by means of a first locking geometry, and is supported on the seat belt shaft or on a component connected to the seat belt shaft in a rotationally fixed manner by means of a second locking geometry, and the section of the ring between the first locking geometry and the second locking geometry is arranged in a non-contact manner relative to the pretensioner drive wheel or relative to a component connected to the pretensioner drive wheel in a rotationally fixed manner, and is arranged in a non-contact manner relative to the seat belt shaft or relative to a component connected to the seat belt shaft in a rotationally fixed manner. Thus, the section between the locking geometries can perform a slight spring movement, which contributes to releasing the positive connection at a defined maximum torque to be transmitted. Furthermore, the ring thus preferably rests only on the seat belt shaft, the pretensioner drive wheel or on a component connected to it in a rotationally fixed manner by means of the first locking geometry and the second locking geometry.

[0022] Furthermore, it is proposed that a locking profile corresponding in shape to the first locking geometry is provided on the pretensioner drive wheel or on a component connected to the pretensioner drive wheel in a rotationally fixed manner, and a locking profile corresponding in shape to the second locking geometry is provided on the seat belt shaft or on a component connected to the seat belt shaft in a rotationally fixed manner. The provided locking profiles enable the ring to contact as flush or flat as possible in the area of the locking geometries.

[0023] Furthermore, it is proposed that at least one first web pointing radially inwards is provided on the pretensioner drive wheel or on a component connected to the pretensioner drive wheel in a rotationally fixed manner, against which the ring laterally abuts. In the installed position, the first web prevents lateral displacement of the ring relative to the pretensioner drive wheel or relative to a component connected to the pretensioner drive wheel in a rotationally fixed manner.

[0024] In this case, it is further proposed that at least one second radially inwardly directed web is provided on the tensioner drive wheel or on a component connected to the tensioner drive wheel in a rotationally fixed manner, the web being arranged at a distance from the first web in the axial direction, and a ring is arranged between the first web and the second web. Due to their spaced-apart arrangement, the first web and the second web form an intermediate space in which the ring can be arranged and then fixed on both sides to prevent lateral sliding. The distance between the second web and the first web in the axial direction corresponds at least to the width of the ring.

[0025] Furthermore, it is proposed that the first web and the second web are arranged offset from each other in the circumferential direction of the tensioner drive wheel or of a component connected to the tensioner drive wheel in a rotationally fixed manner. The offset arrangement creates a gap which facilitates the assembly of the ring by allowing better detection of the alignment of the tensioner drive wheel and the ring visually and, if necessary, with the aid of sensors during automatic assembly. In addition, the gear can thereby be manufactured in a simplified manner as a die-cast part which is produced by means of an opening and closing tool having two tool halves movable relative to each other. The gaps between the webs on one side and the webs on the other side are preferably aligned with each other, and the dimensions of the gaps are designed such that they extend over a larger circumferential portion than the aligned webs, such that the tool halves can be moved apart after the gear has been manufactured without being restricted in their movement by the webs.

[0026] The invention is explained below with reference to preferred embodiments using the drawings. In the drawings:

[0027] Figure 1 a seat belt retractor according to the invention is shown in an exploded view, and

[0028] Figure 2 the gear of a seat belt retractor with a torque limiter before assembly is shown, and

[0029] Figure 3 a cross-sectional view of the gear of a Figure 2 with a torque limiter after assembly is shown, and

[0030] Figure 4 shows Figure 3 an enlarged portion of

[0031] Figure 1Shows a seat belt retractor 1 according to the invention, which has a frame 2 that can be fixedly fastened to a vehicle and a seat belt shaft 3 that is rotatably mounted in the frame. In addition, a force limiting device 20, an irreversible pyrotechnic tensioning device 30, and a main spring unit 40 are provided, which interact with the seat belt shaft 3 in a known manner. Furthermore, a reversible seat belt tensioner 4 with an electric motor 41, a transmission 41, and a tensioner drive wheel 5 is provided. When the reversible seat belt tensioner 4 is activated, the tensioner drive wheel 5 is driven by the electric motor 41 via the transmission 42 in the winding direction of the seat belt shaft 3. To transfer the driving rotational movement of the tensioner drive wheel 5 to the seat belt shaft 3, the clutch is provided with a clutch pawl 19 that is pivotally mounted on the tensioner drive wheel 5, and this clutch pawl controls a positive control movement that engages into the teeth of a gear 8 by means of the rotational movement of the tensioner drive wheel 5. In the controlled position of the clutch pawl 19, the gear 8 thus forms a component that is rotationally fixedly connected to the tensioner drive wheel 5. In addition, a torque limiter in the form of a dimensionally stable ring 6 is provided, and this dimensionally stable ring is arranged between the gear 8 and the seat belt shaft 3 in the Figure 3 and Figure 4 shown mounting position.

[0032] The clutch with the clutch pawl 19 is designed such that when the tensioner drive wheel 5 is driven in a rotational movement by the electric motor 41 via the gear 42, the clutch pawl 19 automatically performs a clutch movement, for example, by frictional force or inertial force. The clutch pawl 19 forms a rotationally fixed connection between the tensioner drive wheel 5 and the gear 8, such that when the clutch is closed, the tensioner drive wheel 5 and the gear 8 can be considered as a rotationally fixed connection in the winding direction of the seat belt shaft 3.

[0033] In Figure 2The gear 8, which can be seen enlarged, is of an annular shape with a central opening and has external teeth on its outer side, into which the clutch pawl 19 engages to establish a rotational connection of the gear 8 with the tensioner drive wheel. The gear 8 has a locking profile 15 in the form of regular teeth on its inner side. Furthermore, the gear 8 has axially spaced webs 17 and 18 on its axial end faces, which project radially inwards into the central opening and, together with the locking profile 15 between them, enclose an annular space. The webs 17 and 18 are each formed as a group of three individual webs, which are arranged such that their centres are arranged at an angle of 120° to each other. Furthermore, the individual webs are spaced such that they each extend over a circumferential part of 60 degrees and each enclose a gap of the same shape between them, which gaps also each extend over a circumferential part of 60 degrees. The individual webs of the webs 17 and 18 are arranged offset from each other in the circumferential direction such that a gap between one web of the group of webs 17 and two webs of the group of webs 18 is aligned in the axial direction.

[0034] The torque limiter in the form of the shape-stable ring 6 can be formed from a metal strip or a plastic ring and has, on its radially outer side, a first locking geometry 7 pointing radially outwards and, on its radially inner side, a second locking geometry 9 pointing radially inwards. The ring 6 is open and its material properties are such that it can be easily expanded or compressed by utilising its elastic properties for assembly. However, the ring 6 remains dimensionally stable such that, during and after being in the assembled state, the ring 6 does not lose its geometry with the first locking geometry 7 and the second locking geometry 9. For the assembly of the ring 6, the ring 6 is slightly compressed and inserted into the central opening of the gear 8, while overcoming one of the webs 17 or 18 on one side. After insertion, the ring 6 is released such that the ring 6 then automatically expands due to its elastic properties. In this way, it achieves a positive engagement of the locking profile 15 of the gear 8 with the first locking geometry 7. The pre-assembled assembly thus composed of the gear 8 and the ring 6 with the second locking geometry 9 is then pushed onto the extension of the seat belt shaft 3. On the extension of the seat belt shaft 3, a locking profile 16 is provided, which corresponds to the shape of the second locking geometry 9, and the ring 6 with the second locking geometry 9 engages into this locking profile 16. The assembly composed of the gear 8, the ring 6 and the seat belt shaft 3 then forms a rotationally fixed connection by means of a positive rotational connection between the gear 8 and the ring 6 and between the ring 6 and the seat belt shaft 3 up to the maximum torque that can be transmitted by the ring 6, wherein the ring 6 forms a central element for the transmission and limitation of torque.

[0035] The ring 6 is arranged in the annular space between the webs 17 and 18 and is fixed by the webs 17 and 18 to prevent lateral displacement. This fixing of the ring 6 in the annular space facilitates the assembly on the extension of the seat belt shaft 3, because when the gear 8 with the ring 6 is pushed onto the extension, the web 17 or 18 forms an abutment for the ring 6 and prevents the ring 6 from being pushed out of the opening of the gear 8.

[0036] The first locking geometry 7 of the ring 6 is formed by radially outwardly directed protrusions 10, each protrusion 10 being formed in the form of a tip having two sides 11 and 12 converging towards each other at an acute angle of less than 45 degrees. The second locking geometry 9 is formed by a plurality of radially inwardly directed protrusions 13, the cross-section of which is partially circular.

[0037] The locking profile 15 on the gear 8 is formed by teeth having grooves, the shape of which corresponds to the shape of the protrusions 10 of the first locking geometry 7. The locking profile 16 on the seat belt shaft 3 is formed by grooves extending in a direction parallel to the direction in which the gear 8 is pushed onto the seat belt shaft 3, the cross-section of which corresponds in shape to the protrusions 13 of the second locking geometry 9, i.e., having a partially circular cross-section here.

[0038] The dimensions of the ring 6 are determined such that it abuts against the seat belt shaft 3 or the gear 8 under the application of spring preloading and is thus fixed. The protrusions 10 of the first locking geometry 7 and the protrusions 13 of the second locking geometry 9 are arranged alternately and equidistantly from each other in the circumferential direction such that equal-length undeformed sections 14 are formed between successive protrusions 10 and 13. The first locking geometry 7 has an even number of protrusions 10, four protrusions 10 in the present embodiment. The second locking geometry 9 has an odd number of protrusions 13, five protrusions 13 in the present embodiment. Thus, the second locking geometry 9 has a greater number of protrusions 13 than the first locking geometry 7, and the protrusion 13 arranged at the free end of the ring 6 is part of the second locking geometry 9. This results in a substantially dimensionally stable connection between the ring 6 and the seat belt shaft 3, or in other words, the ring 6 finds a dimensionally stable support on the seat belt shaft 3 and is positively connected to the seat belt shaft 3 in the circumferential direction via the second locking geometry 9.

[0039] The dimensions of the annular gap between the ring 6 and the gear 8 and the seat belt shaft 3 are designed such that the ring 6 is supported on the seat belt shaft 3 by the protrusions 13 of the second locking geometry 9 and on the gear 8 by the protrusions 10 of the first locking geometry 7, and the section 14 of the ring 6 between the protrusions 10 and 13 is arranged not to contact the seat belt shaft 3 and the gear 8.

[0040] As can be seen from Figure 4As can be seen in the enlarged part, in the case of a radially inwardly directed compressive force F, the projections 10 of the first locking geometry 7 enable the ring 6 to perform a local compression movement due to their shape and the mobility of the utilization section 14. During this period, the ring 6 is supported on the seat belt shaft 3 via the projections 13 of the second locking geometry 9. The spring movement of the ring 6 is additionally promoted because the projections 13 of the second locking geometry 9 and the locking profile 16 on the seat belt shaft 3 are each designed with a partially circular cross-section, and thus a local pivoting movement of the ring 6 in the contact area is achieved by the projections 13 on the seat belt shaft 3. In addition, when a predetermined torque is exceeded, the projections 10 of the first locking geometry 7 promote the local compression movement of the ring 6 due to their shape, because they widen while increasing the angle between the sides 11 and 12, and thus slide out of the locking profile 15 of the gear 8 and cancel the rotational connection. Overall, the cancellation of the rotational connection is improved by the special shape of the projections 10 of the first locking geometry 7 in combination with the shape of the projections 13 of the second locking geometry 9 and the non-contact arrangement of the section 14 of the ring 6, because the projections 10 of the first locking geometry 7 expand better and slide out of the locking profile 15, while the ring with the section 14 can perform a spring movement due to its non-contact arrangement and is supported on the seat belt shaft 3 via the projections 13 of the second locking profile 9.

[0041] Furthermore, if the projections 10 of the first locking geometry 7 do not disengage as expected when the predetermined maximum torque to be transmitted is exceeded, the second locking geometry 9 with radially outwardly directed projections 13 forms an additional limit on the transmissible torque, i.e., additional overload protection, because they spring radially outward and thus cancel the rotational connection between the ring 6 and the seat belt shaft 3.

[0042] In the described embodiment, the ring 6 is directly positively connected to the projections 13 of the second locking geometry 9 in the direction of the driving rotational movement of the tensioner drive wheel 5 via the locking profile 16. However, it can also be positively connected to a component that is rotationally fixed to the seat belt shaft 3 via the second locking geometry 9, and a clutch similar to the clutch between the tensioner drive wheel 5 and the gear 8 can also be provided between the rotationally fixed component and the seat belt shaft 3. In addition, the ring 6 with the first locking geometry 7 can also be directly connected to the tensioner drive wheel 5 in a form-fitting manner.

Claims

1. A seat belt retractor (1), the seat belt retractor comprising: - a seat belt shaft (3) rotatably mounted in a frame (2), the frame being firmly fixable to a vehicle, and a seat belt being windable at one end around the seat belt shaft, and - a reversible seat belt pretensioner (4) which, when activated to pretension the seat belt, drives the seat belt shaft (3) in the winding direction via a pretensioner drive wheel (5) around the seat belt shaft (3), and - a torque limiter arranged between the pretensioner drive wheel (5) and the seat belt shaft (3) for limiting the torque that can be transmitted between the pretensioner drive wheel (5) and the seat belt shaft (3), wherein - the torque limiter is formed by a dimensionally stable ring (6) which is connected in a form-fitting manner in the direction of the torque to be transmitted to the pretensioner drive wheel (5) or to a component connected in a rotationally fixed manner to the pretensioner drive wheel by a first radially outwardly directed locking geometry (7), characterized in that - the dimensionally stable ring (6) is connected in a form-fitting manner in the direction of the torque to be transmitted to the seat belt shaft (3) or to a component connected in a rotationally fixed manner to the seat belt shaft by a second radially inwardly directed locking geometry (9).

2. The seat belt retractor (1) according to claim 1, characterized in that - the first locking geometry (7) is formed by a plurality of radially outwardly directed protrusions (10) spaced apart from each other.

3. The seat belt retractor (1) according to claim 2, characterized in that - the protrusions (10) of the first locking geometry (7) are each formed by a tip having two sides (11, 12) converging towards each other at an acute angle.

4. The seat belt retractor (1) according to any one of claims 1 to 3, characterized in that - the second locking geometry (9) is formed by a plurality of radially inwardly directed protrusions (13) spaced apart from each other.

5. The seat belt retractor (1) according to claim 4, characterized in that - the cross-section of the protrusions (13) of the second locking geometry (9) is partially circular.

6. The seat belt retractor (1) according to any one of claims 2 or 3 and according to any one of claims 4 or 5, characterized in that - the protrusions (13) of the second locking geometry (9) are arranged between the protrusions (10) of the first locking geometry (7) relative to the rotational direction of the pretensioner drive wheel (5).

7. The seat belt retractor (1) according to claim 6, characterized in that - the number of protrusions (10) of the first locking geometry (7) is even and the number of protrusions (13) of the second locking geometry (9) is odd, or vice versa.

8. The seat belt retractor (1) according to any one of claims 6 or 7, characterized in that - the number of the protrusions (10) of the first locking geometry (7) is smaller than the number of the protrusions (13) of the second locking geometry (9).

9. A seat belt retractor (1) according to any one of claims 1 to 8, characterized in that - the dimensionally stable ring (6) is open and abuts against the seat belt shaft (3) or against the component connected to the seat belt shaft (3) in a rotationally fixed manner under spring preloading.

10. A seat belt retractor (1) according to any one of claims 1 to 9, characterized in that - the dimensionally stable ring (6) is supported on the tensioner drive wheel (5) or on the component connected to the tensioner drive wheel (5) in a rotationally fixed manner by means of the first locking geometry (7), and is supported on the seat belt shaft (3) or on the component connected to the seat belt shaft (3) in a rotationally fixed manner by means of the second locking geometry (9), and - the section (14) of the ring (6) between the first locking geometry (7) and the second locking geometry (9) is arranged so as not to contact the tensioner drive wheel (5) or the component connected to the tensioner drive wheel (5) in a rotationally fixed manner, and not to contact the seat belt shaft (3) or the component connected to the seat belt shaft (3) in a rotationally fixed manner.

11. A seat belt retractor (1) according to any one of claims 1 to 10, characterized in that - a locking profile (15) corresponding in shape to the first locking geometry (7) is provided on the tensioner drive wheel (5) or on the component connected to the tensioner drive wheel (5) in a rotationally fixed manner, and - a locking profile (16) corresponding in shape to the second locking geometry (9) is provided on the seat belt shaft (3) or on the component connected to the seat belt shaft in a rotationally fixed manner.

12. A seat belt retractor (1) according to any one of claims 1 to 11, characterized in that - at least one radially inwardly directed first web (17) is provided on the tensioner drive wheel (5) or on the component connected to the tensioner drive wheel in a rotationally fixed manner, and the ring (6) abuts laterally against the first web.

13. A seat belt retractor (1) according to claim 12, characterized in that - at least one radially inwardly directed second web (18) is provided on the tensioner drive wheel (5) or on the component connected to the tensioner drive wheel in a rotationally fixed manner, the second web being arranged at a distance from the first web (17) in the axial direction, and - the ring (6) is arranged between the first web (17) and the second web (18).

14. A seat belt retractor (1) according to claim 13, characterized in that - The first web (17) and the second web (18) are arranged offset from each other in the circumferential direction of the tensioner drive wheel (5) or of the component connected in a rotationally fixed manner to the tensioner drive wheel (5).

Images