Buckle tensioner for a safety belt system

A buckle tensioner for a safety belt system has a buckle head, a drive device for displacing the buckle head, the drive device having an element which is driven in the case of restraint, a tension transfer means connecting the driven element to the buckle head, and an intermediate space between the buckle head and the drive device extending along the tension transfer means. The buckle tensioner further has a housing covering the intermediate space between the buckle head and the drive device and surrounding the tension transfer means. The housing is displaced relative to at least one of the buckle head and the drive device during the tensioning process.

TECHNICAL FIELD 
The invention relates to a buckle tensioner for a safety belt system. 
BACKGROUND OF THE INVENTION 
A buckle tensioner moves the buckle head in the case of retraint by 
approximately 50 to 100 mm towards the anchorage point of the buckle 
tensioner, in order to remove the belt slack from the safety belt system. 
The tensioning process itself takes place abruptly because generally 
pyrotechnic drive units are provided. Parts hindering the tensioning 
process, for example parts transported in the vehicle, must in no way 
protrude into the intermediate space between the buckle head and the drive 
device because the buckle head would strike against this part and it could 
not be displaced through the entire tightening distance. In addition, a 
risk of injury to occupants of the vehicle exists in known buckle 
tensioners for the instance which in fact scarcely occurs in practice but 
is theoretically not ruled out, that during the tensioning process, 
fingers of the occupant of the vehicle protrude into the intermediate 
space between buckle head and drive device, which would then be jammed. 
BRIEF SUMMARY OF THE INVENTION 
The invention provides a buckle tensioner in which both the risk of an 
accident and also the risk that the tightening distance is limited by 
parts extending into the intermediate space between buckle head and drive 
device is ruled out. 
The buckle tensioner according to the invention has a buckle head, a drive 
device for displacing the buckle head, the drive device having an element 
which is driven in the case of restraint, a tension transfer means 
connecting the driven element to the buckle head, and an intermediate 
space between the buckle head and the drive device extending along the 
tension transfer means. The buckle tensioner further has a housing 
covering the intermediate space between the buckle head and the drive 
device and surrounding the tension transfer means. The housing is 
displaced relative to at least one of the buckle head and the drive device 
during the tensioning process. 
The housing can be constructed very simple and is, in addition, able to be 
mounted quickly. The buckle head and/or the drive device travel, viewed 
relatively, into the housing during the tensioning process. It is very 
important that the housing is stiff enough in order to prevent an occupant 
from pressing together the housing . A bellow does not define a housing, 
i.e. a protection means according to the invention since a bellow is soft 
and flexible and has folds which protrude into the intermediate space. 
Therefore, the fingers of the occupant may protrude into the folds and 
into the intermediate space. 
The housing can be an elongated cylindrical or tubular body surrounding the 
tension transfer means completely in the circumferential direction. It is 
preferably fastenend to the buckle head or to the drive device and is 
slipped over the respectively other of the two parts on the other side of 
the latter, so that it can be displaced along the outer surface of the 
latter in the case of restraint. 
The drive device, which preferably is a piston/cylinder unit, comprises a 
cylinder on which an ignition unit is secured on the outer side in the 
region of the end facing the buckle head. The housing projects in axial 
direction not only partially over the cylinder but also over the ignition 
unit. 
The housing can also be of a material which is to a certain, limited extent 
elastically flexible, which permits a certain bending. This can be 
advantageous for example when the tension transfer means is constructed so 
as to be flexible, for example as a tension cable, and the position of the 
belt buckle relative to the drive device is not clearly defined. 
According to one embodiment the housing consists not of one but of several 
housing parts which, during the tensioning process, are able to be pushed 
into each other in the manner of a telescope. The housing or housing parts 
can then also be formed in one piece on the buckle head housing or on the 
housing of the drive device. 
In an embodiment in which the buckle tensioner is integrated in a vehicle 
seat and the vehicle seat has a lateral recess to receive the buckle 
tensioner, the housing is constructed in a shell-shaped manner. As it is 
shielded on one side by the vehicle seat, it no longer has to completely 
surround the tension transfer means externally, but only the region which 
is freely accessible from the exterior.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
In FIG. 1, a buckle tensioner 1 for a safety belt system is shown, which 
has a buckle head 3, of which only the outer housing is shown, a drive 
device 5 in the form of a piston/cylinder unit and also a tension transfer 
means 7 in the form of a tension cable. The tension transfer means 7 
connects the buckle head 3 with an element which is driven in the case of 
restraint, namely the piston which is not shown in further detail. On the 
outer side of the cylinder 9, an ignition unit 11 is fastened, which 
serves to ignite a pyrotechnical propellant (not shown) in the case of 
restraint. The tension transfer means 7 is completely surrounded in 
circumferential direction by a housing 13. The housing 13, which is of 
elastic plastic, for example PE, is thin-walled and has a thickness of 
only 0.5 to 0.7 mm, whereby it is given a certain bending elasticity. 
However, the housing 13 is stiff enough to prevent it from being pressed 
together by the occupant. On the outer housing of the buckle head 3, in 
the region of the end facing the drive device 5, a shoulder 15 is 
provided, onto which the housing 13 is placed with a press fit. The 
geometry of the housing 13 in the region of its end on the drive side, 
where it is slipped over the end of the drive device 5 facing the buckle 
head 3 and the ignition unit 11, is adapted relatively exactly to the 
outer contour of the drive device 5 and the ignition unit 11. However, a 
minimal play is provided between the housing 13 and the outer contour of 
drive device 5 and ignition unit 11, enabling a displacement of the 
housing 13 in axial direction, more detailed in the direction of the arrow 
A during the tensioning process. 
The housing 13 which is constructed as a separate part represents an 
extension of the buckle head housing to beyond the end of the cylinder 9 
facing the buckle head 3. The contour adapted to the buckle head housing 
at the end of the housing 13 on the buckle head side continues towards the 
end on the drive side into the outer contour of drive device 5 and 
ignition unit 11, so that the buckle tensioner 1 has a closed outer 
contour towards the exterior without distinct recesses or undercuts. The 
housing 13 covers an intermediate space 17 around the tension transfer 
means 7 and between the buckle head 3 and the drive device 5 toward the 
exterior, so that it is ruled out that parts, such as parts which are to 
be transported, pieces of clothing or even the fingers of the occupant of 
the vehicle reach into this intermediate space 17 into which the buckle 
head 3 moves in the case of restraint as it is possible with a bellow. 
If in a case of restraint the ignition unit 11 ignites the propellant and 
the piston moves the tension transfer means 7 and hence the buckle head 3 
downwards, the latter also takes with it the housing 13 in its movement 
downwards. The housing 13 slides unimpeded along the outer surface of the 
cylinder 9 and along that of the ignition unit 11, because no projecting 
parts are provided either on the cylinder 9 or ignition unit 11. 
In the embodiment illustrated in FIG. 3, the housing 13 is composed of two 
housing parts which are displaceable into each other in the manner of a 
telescope, the upper housing part 19 forming a pot-like extension of the 
buckle head housing, i.e. being connected in one piece with the buckle 
head housing. The lower housing part 21, which projects into the upper 
housing part 19, is fixedly connected with the cylinder 9 and has a 
thickened region 23, running in a spiral form, and also regions with small 
wall thickness therebetween, so that altogether a bending elasticity is 
achieved. This has the advantage that the housing parts 19, 21 can adapt 
to an arc-shaped path of the tension transfer means 7, as is indicated in 
FIG. 3. The buckle head 3 is in fact inclined in the direction of the 
occupant of the vehicle when the insertion tongue 25 is introduced. The 
housing 13 can possibly also have recesses, in order to give it the 
necessary bending elasticity. 
In the embodiment illustrated in FIGS. 4 to 6, the buckle tensioner 1 is 
integrated in the vehicle seat and the drive device 5 is fastened to the 
seat frame 29. The seat part 31 of the vehicle seat, as can be seen from 
FIG. 6, has on its rear corner a recess which is dimensioned so that the 
buckle head 3 and the housing 13 do not project laterally with respect to 
the seat part 31. The housing 13 can be constructed as a hollow body which 
is closed in circumferential direction or as a shell which closes off the 
intermediate space to the exterior. In the embodiment illustrated in FIG. 
5, the housing 13 is not fastened to the buckle head 3, but rather either 
to the seat part 31 or to the drive device 5. During the tensioning 
process, the buckle head 3 penetrates almost completely into the 
intermediate space 17. The tightening path is marked by S. 
FIG. 6 shows two embodiments of the housing 13, which differ from each 
other by different outer contours. On the one hand, it is possible that 
the housing 13 has a wall 33 which runs along the recess of the seat part 
31, on the other hand the housing 13 can have a wall 35 which runs on the 
side of the buckle tensioner facing away from the seat part 31 and defines 
the outer contour of the seat part 31 without the recess for the buckle 
tensioner. 
In the embodiment shown in FIGS. 7 and 8, the buckle head 3 penetrates 
almost completely into the housing 13 in the case of restraint which, in 
so doing, widens. The position of the buckle head 3 after the tensioning 
process is indicated by broken lines. Two projections 53 on the inner side 
on the housing 13, lying opposite each other and visible in FIG. 8, 
prevent a movement of the housing 13 relative to the drive device in the 
case of restraint. In the region of its upper end, two opposed lateral 
protrusions 51 are constructed on the buckle head 3 with which the buckle 
head 3 strikes against the upper end face of the housing 13. The 
protrusions 51 prevent the buckle head 3 from penetrating too deep into 
the housing 13 and prevent the release button 49 from subsequently no 
longer being able to be actuated. The projections 53 can be constructed so 
that they yield laterally when the protrusions 51 meet the housing 13 and 
only permit a relative movement of the housing 13 to the drive device in 
the final phase of the tensioning process. In this embodiment, each of the 
buckle head 3 and the drive device 5 accordingly move relative to the 
housing 13. 
Depending on the position of installation, the housing 13 can be partially 
open in the circumferential direction.