The invention relates to a method to control a seatbelt device comprising the features of to the preamble of claim 1 and a seatbelt device comprising the features of the preamble of claim 5.

Seatbelt devices are used in vehicles to restrain the passengers in order to prevent severe injuries. The seatbelt device comprises several belt sections, one or more retractors, a tongue which is slidable on one of the belt sections or which separates the different belt sections and a vehicle-fixed buckle in which the tongue may be locked.

One well known approved seatbelt device comprises a seatbelt with 3-point geometry in the fastened position with a diagonal belt section crossing the chest of the occupant and a pelvis section crossing the pelvis of the occupant.

A seatbelt device with a 3-point geometry like described above is known for example from the DE 10 2010 034 040 B4.

One essential criterion of seatbelts regarding the load of the occupant is the chest deflection caused by the diagonal belt section. It has been shown that the chest deflection depends on the different restraining forces acting from the upper end (B3 ) and from the lower end (B4 ) of the diagonal belt section.

In the DE 10 2010 034 040 B4 it is suggested to provide both ends B3 and B4 of the diagonal belt section with load limiting devices, wherein the load limiting level of the load limiting device of the lower end B4 is lower than the load limiting level of the load limiting device of the upper end B3.

Another problem to be regarded when restraining the occupant is that the occupant may not dive with the pelvis under and through the pelvis belt section. This movement is also designated as submarining.

Therefore the obj ect of the invention can be seen therein to provide a method to control a seatbelt device and to provide seatbelt device which enables an improved restraining of the occupant with a reduced chest deflection.

According to the invention it is suggested a method comprising the features of claim 1 and a seatbelt device comprising the features of claim 5. Further preferred embodiments of the invention can be obtained from the subclaims, the figures and the related description.

According to the method of claim 1 it is suggested that the lower end of the diagonal belt section is provided with a re ^¬ lease mechanism which is activated in a crash with a first predetermined time delay.

The crash begins per definition when the vehicle sensor device detects an unavoidable impact at the time tO. The occupant starts to move forward at the time tO, wherein the pelvis moves together with the torso of the occupant in the impact direction . The chest deflection increases with the movement of the torso. At the same time the tendency of the pelvis to dive under and through the pelvis belt decreases with the torso inclining forwardly in impact direction. According to the idea of the invention the lower end of the diagonal belt section is released by a release mechanism, so the chest deflection may be therefore reduced. As the release is activated with a time delay the likelihood of submarining is reduced at the same time. Therefore the release of the lower end of the diagonal belt section with the time delay results in a reduced chest deflection without or with only minor acceptable disadvantages for the restraining characteristic especially regarding the submarining .

Furthermore it is suggested that the first predetermined time delay is at least 65 ms with respect to the start of the crash. It has been shown that the torso and the occupant is after the time delay of 65 ms in a position in which the pelvis does not move forward anymore, the pelvis can be seen as fixed, so that the release of the lower end does not result in a further forward movement of the pelvis but only in a reduction of the chest deflection.

According to another preferred embodiment it is suggested that the upper end of the diagonal belt section is provided with a load limiting device having at least two different load limiting levels, wherein the load limiting level is switched after a predetermined time from a high load limiting level to a low load limiting level, and the release mechanism is activated with a second predetermined time delay after switching the load limiting device from the high to the low level. The load limiting device with the different load limiting levels also called adaptive load limiting device ( LLA ) enables an improved restraining characteristic, with reduced restraining forces while the forward movement when the low load limiting level acts. The restraining forces are switched from a high level to the low level. Measurements have shown that the restraining forces are reduced by the switching but the restraining forces are increased immediately afterwards to a peak because of the kinetic energy of the occupant. It has shown that the peak can be reduced by the activation of the release mechanism, which results in an increase of the belt slack and a further reduc ^¬ tion of the chest deflection. In this case the second predetermined time delay is preferably at least 5 ms .

Furthermore a seatbelt device is suggested, in which the lower end of the diagonal belt section is provided with a release mechanism which feeds belt slack into the diagonal belt see- tion when activated.

In this case a vehicle-fixed buckle is preferably provided, and the seatbelt is provided with a slidable tongue, wherein the tongue is lockable in the buckle and subdivides the seat- belt in the diagonal belt section and a pelvis belt section when locked in the buckle, and the release mechanism is arranged at the buckle. The release mechanism is realized in the case by a mechanism which moves the buckle towards the diagonal belt section and feeds therefore belt slack into the diagonal belt section.

As the release mechanism is activated to feed belt slack after predetermined time delays the release mechanism may comprise preferably a time triggered activation mechanism.

Furthermore it has shown that the release mechanism may be designed preferably to pay out an amount of 50 to 100 mm of belt slack into the diagonal belt section to reduce the chest de ^¬ flection especially when activated after the switching of an adaptive load limiting device. If the seatbelt device comprises additionally a reversible or irreversible pretensioner the release mechanism may be realized preferably by a reverse operating of the pretensioner. So the release mechanism is realized by an already used part, wherein the pretensioner pulls the slack out of the seatbelt so the lower end of the diagonal belt section is already in a pulled back position, from which the release mechanism realized by the reverse operating pretensioner feeds the slack back into the seatbelt by moving the lower end back to the original position or further to a forward directed position related to the original position.

In the following the invention shall be illustrated on the basis of preferred embodiments with reference to the accompanying drawings, wherein:

Fig. 1 shows a seatbelt device with a conventional 3-point geometry according to the prior art; and

Fig. 2 shows a seatbelt device with a release mechanism arranged at the lower end of the diagonal belt section; and

Fig. 3 shows the restraining forces in the diagonal belt

section with an adaptive load limiting device with release mechanism and without a release mechanism; and

Fig. 4 shows the chest deflection when restraining the occupant with a release mechanism and without a release mechanism; and Fig. 5 shows the release mechanism with different force lev els; and

Fig. 6 shows the different chest deflections for the differ ent force levels; and

Fig. 7 shows a buckle with a mechanical release mechanism.

In Figure 1 it is shown a seatbelt device 1 having the conventional 3-point-geometry with a seatbelt 11 comprising a pelvis belt section 2 and a diagonal belt section 3, which are sepa ^¬ rated by a tongue 6 locked in a buckle 5 like described in the DE 10 2010 034 040 B4. The pelvis belt section 2 is attached with the free end B6 via a not shown bracket at the vehicle structure, wherein the free end B6 might also be connected with an irreversible or reversible pretensioner . The pelvis belt section 2 crosses the pelvis starting from the free end B6 towards the tongue 6 and ends in the end B5 at the buckle 5. The diagonal belt section 3 extends from the lower end B4 at the buckle 5 across the chest of the occupant towards the upper end B3 at which the seatbelt 11 is deflected or it is wound upon a spindle of a retractor 9. The retractor 9 may be equipped additionally with an irreversible or reversible pretensioner 8. The diagonal belt section 3 is loaded when restraining the occupant from the lower end B4 by a force FI and from the upper end B3 by a force FIX, which results in forces FNI and FNII acting on the occupant and a total force FRES acting at the center 4 of the diagonal belt section 3. The Figure 1 of DE 10 2010 034 040 B4 and the related description is incorporated in this application by reference, wherein the related description is not repeated in this application to shorten the application. The reference numbers are contained in the application text of the DE 10 2010 034 040 B4, so the DE 10 2010 034 040 B4 must be considered regarding the Figure 1. In the DE 10 2010 034 040 B4 the seatbelt geometry, the restraining forces and the chest deflection resulting therefrom are explained in detail.

The seatbelt device 1 according to the invention is shown in Figure 2. The seatbelt device 1 is provided at the lower end B4 of the diagonal belt section 3 with a release mechanism 12, which may feed a belt slack of 50 to 100 mm into the diagonal belt section 3 when activated. Furthermore the seatbelt device 1 is provided with a load limiting device 7 which comprises a mechanism to realize a first high load limiting level in a first step for a predetermined time or pay out belt length and which may be switched to a second low load limiting level, which is also called adaptive load limiter (LLA) in the products of the applicant. The high load limiting level is designed in the shown embodiment to 5,3 kN and the low load limiting level is designed to 1,5 kN like shown in Figure 3 by the curve I. Instead of the described load limiting levels also other load limiting levels depending on the vehicle structure and depending on the position of the seat may be realized. The load limiting level is switched in the described load limiting device 65 ms after t0 , which is the time when the control unit calculates an unavoidable crash based on the signal of the relevant sensor devices. When the load limiting device 7 is switched the restraining force acting on the chest of the occupant is reduced with in a very short time from 5,3 kN to less than 1 kN. Afterwards the restraining force increases in a peak to nearly 2 kN before it decreases again up to 1,5 kN, which is the designed low load limiting level of the adaptive load limiter. In Figure 4 it is shown the chest deflection III resulting from the load limiting shown in curve I in Figure 3. The chest deflection increases with a time delay to the restraining force up to nearly 35 mm in 70 ms after tO. Afterwards the chest deflection decreases quickly down to 22 mm within 2 to 4 ms because of the switching of the load limiting device 7 to the low level of 1,5 kN before it increases again to a second peak up to 35 mm in 85 ms after tO.

The curve II in Figure 3 shows the force acting on the occupant,, when the release mechanism 12 is activated with a first time delay of 71 ms related to the time tO the start of the crash or with a second time delay of 6 ms related to the switching of the load limiting device 7 down to the low load limiting level. The increase of the restraining force after switching the load limiting device 7 can be reduced significantly which is shown by the arrow B. The same effect can be seen in the chest deflection shown by the curve IV in Figure 4, which means the load of the occupant also can be reduced and the risk of injuries therefore can be lowered. The release mechanism 12 feeds about 50 to 100 mm of belt slack into the diagonal belt section 3.

In the Figures 5 and ^' 6 are shown different curves C, D and E of the chest deflection which may be obtained by applying different force levels in the release mechanism 12. It is significant that the chest deflection depends on the force level, and the chest deflection is reduced more, when the force level of the release mechanism 12 is low. An optimum of the reduction of the chest deflection can be achieved when the force level of the release mechanism 12 is 0, which means the release mechanism should feed the slack as quickly as possible and with no restraining force into the diagonal belt section 3.

In Figure 7 it is shown one possible embodiment of the release mechanism with a very easy design structure. The buckle 5 is provided with a flexible cable 13 and a tube 17 with a deflection section 18 close to an opening 19, through which the cable 13 is introduced into the tube 17. The cable 13 is provided at the end with retaining element 14 which is abutting at the rear side of a blocking structure 15, so that the buckle 5 is blocked against a movement when the seatbelt pulls the buckle. The release mechanism 12 is activated by releasing the blocking structure 15, which may be realized by destroying the blocking structure or by releasing the blocking structure 15 by a not shown actuator. After the blocking structure 15 is released the cable 13 is not blocked by the retaining element 14 and may move together with the buckle 5 in the arrow direction towards the diagonal belt section 3 to feed the slack into the diagonal belt section 3. Furthermore a spring 16 is provided, which is supported at an axial abutment and positioned face to the retaining element 14 which stops the movement of the buckle as a soft stop.