GB2525154A

GB2525154A - Load Limiting device for a seat belt of a vehicle

Info

Publication number: GB2525154A
Application number: GB1402390.7A
Authority: GB
Inventors: Kalyan Cheruvu; Lutz Quarg
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2014-02-12
Filing date: 2014-02-12
Publication date: 2015-10-21
Also published as: GB201402390D0

Abstract

The invention relates to a load limiting device 10 for a seat belt of a vehicle, the load limiting device comprising a spool (12 fig. 1) for the seat belt, the spool being rotatable about a rotation axis (14 fig. 1) due to unwinding the seat belt from the spool. At least one first load limiting element 18 and at least one second load limiting element 20 having at least one knife edge 22 and are at least indirectly connected to the spool and rotatable about the rotation axis. The second load limiting element is movable away from the rotation axis from a release position into at least one load limiting position due to centrifugal forces acting upon the second load limiting element. The centrifugal forces result from rotating the spool when unwinding the seat belt. When in the load limiting position, the second load limiting element is in contact with the first load limiting element at least temporarily and shears the first load limiting element by means of the knife edge thereby retarding the rotation of the spool. The spool can be connected to the second load limiting element via at least one torsion bar.

Description

Load Limiting Device for a Seat Belt of a Vehicle The invention relates to a load limiting device for a seat belt of a vehicle.

ER 1 717 115 A2 shows a seat bolt retractor comprising a spool which retracts a seat belt, a locking member which is normally rotatably integrally with the spool, a lock mechanism which is activated under an emergency situation and locks the locking member to prevent the locking member from rotating in a belt-retracting direction, a torsion bar linking the spool and the locking member, the torsion bar normally linking the spool and the locking member in an integrally rotatable manner, the torsion bar being twisted when the locking member is locked by a lock mechanism with respect to the belt-retracting direction, and a pretensioner which is activated under the emergency situation so as to generate a driving force.

The seat belt is retracted with the driving force of the pretensioner in an initial stage of the emergency situation, wherein a load applied to the seat belt is limited by twisting the torsion bar when the locking member is locked by the lock mechanism with respect to the belt-retracting direction. The locking member is provided with a quick-lock member for locking the spool to prevent the spool from rotating in a belt-withdrawing direction when the spool is rotated rapidly in the belt-retracting direction responds to the actuation of the pretensioner.

It is an object of the present invention to provide a load limiting device by means of which the load acting upon a seat passenger via the seat belt due to an accident can be limited in a particularly advantageous need-based manner.

This object is solved by a load limiting device having the features of patent claim 1.

Advantageous embodiments with expedient and non-trivial developments of the invention are indicated in the other patent claims.

In order to provide a load limiting device by means of which loads acting upon a seat passenger via the seat belt due to an accident can be limited in a particularly advantageous need-based manner, the load limiting device according to the present invention comprises a spool for the seat belt, the spool being rotatable about a rotation axis due to unwinding the seat belt from the spool. Moreover, the load limiting device comprises at least one first load limiting element. Furthermore, the load limiting device comprises at least one second load limiting element having at least one knife edge. The second load limiting element is connected to the spool at least indirectly.

Furthermore, the second load limiting element is rotatable about the rotation axis. Thus, the second load limiting element can be rotated by rotating the spool about the rotation axis. The second load limiting element is movable away from the rotation axis from a release position into at least one load limiting position due to centrifugal forces acting upon the second load limiting element, the centrifugal forces resulting from rotating the spool when unwinding the seat belt from the spool. This means the spool, and, thus, the second load limiting element are rotated about the rotation axis by unwinding the seat belt from the spool.

Thus, centrifugal forces act upon the second load limiting element so that the second load limiting element is moved from the release position into at least one load limiting position.

In the load limiting position, the second load limiting element is in contact with the first load limiting element at least temporarily and shears the first load limiting element by means of the knife edge when rotating the second load limiting element about the rotation axis.

The speed of the spool about the rotation axis depends on the speed at which the seat belt is unwound from the spool. The speed at which the seat belt is unwound from the spool depends on the size and, thus, on the weight of a seat passenger to be restrained by the seat belt in the case of an accident.

In the load limiting position, the second load limiting element shears the first load limiting element. Thereby, the spool, and, thus, the seat belt are slowed down so that the load exerted by the seat belt on the seat passenger is adjusted or affected. Since the movement of the load limiting element depends on the weight of the seat passenger, the load limiting effect provided by the load limiting device also depends on the weight and the size of the passenger. Thereby, an efficient restraint system behaviour with a dynamic load limiting effect for different seat passengers or occupants can be realized.

In other words, the load is limited automatically without using sensors or actuators. The idea behind the load limiting device according to the present invention is that the speed of the seat belt is used for realizing a dynamic load limiting effect and that the speed of the seat belt depends on the weight and the size of the occupant. For example, a 95th percentile occupant causes a higher seat belt speed than a 5O percentile occupant. The 50th percentile occupant causes a higher seat belt speed than a 5O percentile occupant.

The higher the seat belt speed, the higher the rotational speed of the spool and the second load limiting element about the rotation axis.

Further advantages, features, and details of the invention derive from the following description of a preferred embodiment as well as from the drawing. The features and feature combinations previously mentioned in the description as well as the features and feature combinations mentioned in the following description of the figures and/or shown in the figures alone can be employed not only in the respective indicated combination but also in any other combination or taken alone without leaving the scope of the invention.

The drawing shows in: Fig. 1 a schematic longitudinal sectional view of a load limiting device for a seat belt of a vehicle, the load limiting device comprising at least one load limiting element being movable by centrifugal forces resulting from unwinding the seat belt from a spool connected at least indirectly to the load limiting element; Fig. 2 a schematic front view of the load limiting device; and Fig. 3 a further schematic front view of the load limiting device.

Figs. ito 3 show a load limiting device 10 for a seat belt of a vehicle, in particular a motor vehicle. The load limiting device 10 comprises a spool 12 being rotatable about a rotation axis 14 due to unwinding the seat belt from the spool 12. In other words, the seat belt can be wound onto the spool 12 and unwound from the spool 12. The load limiting device 10 comprises at least one locking means 16 for rotationally locking the spool 1230 that the spool 12 cannot be rotated about the rotation axis 14. For example, the locking means 16 is configured as a surface via which the spool 12 can be rotationally fixed by, for example, a frictional brake.

The load limiting device 10 further comprises a first load limiting element 18 shown in Fig. 2. With respect to the rotation axis 14, the load limiting element 18 is rotationally fixed so that the spool 12 is rotatable about the rotation axis 14 in relation to the first load limiting element 18. The load limiting device 10 further comprises a second load limiting element 20 having a knife edge 22. The second load limiting element 20 is connected to the spool 12 via a wheel block 24 having two components 26 and 28. The component 26 is rotationally connected to the component 28 via respective locking latches 33 of the component 26 and locking teeth 34 of the component 28. The component 28, and, thus, the wheel block 24 arc connected to the spool 12 via a torsion bar 30 of the load limiting device 10. Thus, the second load limiting element 20 is connected to the spool 12 via the wheel block 24 and the torsion bar 30.

On one side, the torsion bar 30 is connected to the component 28. On the other side, the torsion bar 30 is connected to the spool 12. The torsion bar 30 is free to rotate on the one side. If, for example, the torsion bar is rotationally fixed on the other side and the component 28 is rotated about the rotation axis 14, the torsion bar 30 is twisted. The wheel block 24 and the second load limiting element 20 are rotatable about the rotation axis 14. Moreover, the second load limiting element 20 is movable away from the rotation axis 14 from a release position shown in Fig. 2 into at least one load limiting position shown in Fig. 3 due to centrifugal forces acting upon the load limiting element 20, the centrifugal forces resulting from rotating the spool 12 when unwinding the seat belt from the spool 12.

In the load limiting position, the second load limiting element 20, in particular, the knife edge 22 comes into contact with the first load limiting element 18 at least temporarily and shears the first load limiting element 18 by means of the knife edge 22 when rotating the spool 12 and, thus, the second load limiting element 20 about the rotation axis 14. The load limiting device 10 further comprises at least one spring 32 which is compressed and, thus, loaded when the load limiting element 20 moves from the release position into the load limiting position.

Since the load limiting element 20 shears the load limiting element 18, the rotational speed of the load limiting element 20 is decreased. Thereby the speed at which the seat belt is unwound from the spool 12 is decreased.

For example, if a frontal impact occurs, an occupant to be restrained by the seat belt is moved forwards due to the frontal impact. Preferably, at the beginning of this accident the torsion bar 30 is locked on the other side whereas the one side is free to rotate. In the further process, the seat belt is unwound from the spool 12 thereby causing a rotational movement of the spool 12, and, thus, the load limiting element 20 about the rotation axis 14. Especially, the speed of the seat belt and, thus, the rotational speed of the second load limiting element 20 about the rotation axis 14 depend on the size and weight of the occupant so that the movement of the load limiting element 20 out of the release position into the load limiting position depends on the size and weight of the occupant.

Thus, a need-based load limitation can be provided by the load limiting device 10 in a very and cost-efficient way since no sensors and actuators are used. Once a knife edge 22 is in contact with the fixed load limiting element 18 being a fixed mass, further forces in addition to torsional forces in the torsion bar 30 act upon the spool 12 due to the material cutting process. Said additional forces are an additional resistance for the rotation of the torsion bar 30 so that the forward movement of the occupant is restricted.

The load limiting device 10 can be particularly advantageously used for a second row of seats and thereafter and can help avoid head contact of occupants with interior components. The load limiting device 10 can also be used for front occupants of the vehicle.

List of reference signs load limiting device 12 spool 14 rotation axis 16 locking means 18 first locking element second locking element 22 knife edge 24 wheel block 26 component 28 component torsion bar 32 spring 33 locking ledge 34 locking teeth