Re-tightener with pyrotechnic propellant charge for safety-belt automatic wind-up devices

Retightener with a pyrotechnic propellant charge for automatic safety-belt wind-up devices having an energy converter, wherein in the event of danger the explosive pressure of the ignited propellant charge acts on a pullout element tightening the safety belt around the body of the vehicle passenger to be protected via a liquid buffer arranged between the propellant charge and a pullback element. In accordance with the invention a receptacle which contains the liquid buffer is coupled to the winding shaft and rotates together with the latter. In the circumferential surface of the receptacle is at least one jet nozzle directed substantially tangentially to the axis of rotation and against a stationary guide ring surrounding the receptacle.

CROSS-REFERENCE TO RELATED APPLICATION 
The following application, assigned to REPA Feinstanzwerk GMBH, the 
assignee of the present application, is hereby incorporated by reference: 
U.S. application Ser. No. 834,794, filed for Artur Foohl, on Sept. 19, 
1977. 
FIELD OF THE INVENTION 
The invention relates to a retightener or pullback device with a 
pyrotechnic propellant charge for safety-belt automatic windup devices 
having an energy converter, wherein in the event of danger the explosive 
pressure of the ignited propellant charge acts on a pullback element 
tightening the safety belt around the body of the vehicle passenger to be 
protected, via a liquid buffer arranged between the propellant charge and 
a pullback element. 
DESCRIPTION OF THE PRIOR ART 
In the above-mentioned pullback device according to related U.S. 
application Ser. No. 834,794, the liquid buffer or liquid medium is thrown 
against a free-standing turbine wheel through a jet nozzle by the firing 
of the propellant charge in the event of danger, whereby the pullback 
element is set in rotation and the safety belt is tightened around the 
body of the vehilce passenger. 
Contrary thereto, in another known wind-up device for eliminating the belt 
slack of a safety belt system, German Published Non-Prosecuted Application 
No. 26 25 573, a pullback torque is obtained by the provision that a 
liquid buffer located in the hollow winding shaft for the safety belt is 
pushed by the explosive pressure of a propellant charge through radial 
holes of a wheel connected to the winding shaft at high speed by means of 
an axially movable piston, whereby a rotary impulse is imparted to the 
wheel. A disadvantage is here the circumstance that the volume of liquid 
is relatively small and the pulse duration short, so that in this drive 
system the pulse amplitude is relatively small. Also, the system is 
expensive to produce due to the presence of relatively long discharge 
holes of small cross section. 
SUMMARY OF THE INVENTION 
It is now an object of the present invention to provide a pullback device 
of the type described with improved efficiency and mechanical design. 
With the foregoing and other objects in view, there is provided in 
accordance with the invention, a retightener for safety-belt automatic 
wind-up devices having a winding shaft mounted in a bearing block, a 
safety belt wound around the shaft, a retightening element connected to 
the shaft, with a pyrotechnic propellant charge which when activated by 
firing the charge generates an explosive pressure on the retightening 
element to tighten the safety belt around the body of a motor vehicle 
passenger to be protected and a liquid medium disposed intermediate the 
retightener and the pyrotechnic propellant charge, the improvement 
including a receptacle having a circumferential surface containing the 
liquid medium coupled to the winding shaft and rotated with the winding 
shaft, and at least one jet nozzle disposed in the circumferential surface 
of the receptacle directed substantially tangentially to the axis of 
rotation of the winding shaft and against a stationary guide ring 
surrounding the receptacle. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in a 
retightener with pyrotechnic propellant charge for safety-belt automatic 
wind-up devices, it is nevertheless not intended to be limited to the 
details shown, since various modifications may be made therein without 
departing from the spirit of the invention and within the scope and range 
of equivalents of the claims.

DETAILED DESCRIPTION OF THE INVENTION 
According to the invention, a receptacle, which contains the liquid buffer, 
is coupled to the winding shaft and rotates with the latter. The 
receptacle has in its circumferential surface at least one jet nozzle 
directed substantially tangentially to the axis of rotation and against a 
stationary guide ring which surrounds the receptacle. The guide ring 
preferably has guide vanes which are bent toward the receptacle and are 
directed substantially perpendicularly to the jet direction of the jet 
nozzle. In this connection it is advantageous to provide a multiplicity of 
such jet nozzles on the circumference of the receptacle which may have the 
shape of a capsule. The guide ring, which surrounds the circumference of 
the receptacle, covers the jet nozzle or nozzles with only little spacing 
between nozzle and guide ring. The guide ring together with the receptacle 
form a largely closed turbine system, wherein the liquid jet issuing from 
the jet nozzles when the propellant charge is fired, hits the guide ring 
or its guide vanes directly and, due to the short distance between the jet 
nozzle and the guide ring, the jet is highly concentrated, and thereby 
imparts a strong rotary impulse to the rotatable receptacle. The liquid 
can subsequently run unimpeded, laterally off the guide ring. A particular 
advantage is the circumstance that substantially larger amounts of liquid 
can be accommodated in such a rotatable receptacle than, for instance, in 
the hollow winding shaft of the aforementioned known system. The 
efficiency of the pullback device according to the invention is high, for 
one reason that the liquid jet or jets leave the receptacle tangentially 
to the winding shaft and hit the directly adjacent guide vanes of the 
guide ring practically perpendicularly. 
According to a further embodiment of the invention, a tubular displacement 
element for the liquid buffer, which can be radially expanded by the 
explosive pressure of the propellant charge against the jet nozzle or jet 
nozzles distributed over the receptacle circumference is arranged in the 
liquid chamber of the receptacle. This displacement element has the effect 
of a driving piston but, as compared to driving pistons of known systems, 
has the advantage of radial expandability and therefore, of a larger 
displacement volume per unit time. 
According to a further embodiment of the invention, the displacement 
element is designed in a simple manner as a flexible, flat spiral spring 
which can expand under pressure. In accordance with an alternative 
embodiment, the displacement element can also be provided in the form of a 
tube which consists of easily deformable material and has folded ribs. 
Within the scope of the invention, still other displacement elements can, 
of course, also be used, such as elastic diaphragms or the like. 
The mechanical design of the pullback device according to the invention is 
simplified by the provision that the receptacle, together with an axial 
extension containing the propellant charge, forms a rotatable structural 
unit which can be coupled to the winding shaft. The manufacture as well as 
the assembly of the individual parts forming the pullback device according 
to the invention is substantially simplified if the extension containing 
the propellant charge is part of a screw cap which closes off the 
cup-shaped receptacle and is connected to a stationary ignition contact 
device consisting of a slip ring and brushes. 
Further advantageous details of the invention will be seen from the 
embodiment example described in the following and shown in the drawings. 
Referring to FIGS. 1 and 2, a fitting or anchoring plate 2 of an automatic 
safety-belt wind-up device can be fastened by means of a hole 1, for 
instance, to the body frame of a motor vehicle. Support extensions 3 and 4 
are arranged on both sides of plate 2 and a winding shaft 5 for the safety 
belt 6 is rotatably supported in support extensions 3 and 4. Rigidly 
fastened to the support extension 4 is a guide ring 7, which has at its 
cylindrical ring portion a multiplicity of stamped-out guide vanes 8, 
which are bent toward the center of the ring. 
A structural unit which can be slipped and coupled onto the end of the 
winding shaft 5 protruding beyond the support extension 4, consists of a 
cupshaped receptacle 9, a cup-shaped screw cap 10 and a coupling ring 11. 
The shaft end engages in a hole of the receptacle 9 and is coupled to the 
latter by means of a coupling boss 12 or the like. The receptacle 9 at its 
cylindrical circumference has at the height of the guide ring 7 several 
jet nozzles 13 directed substantially tangentially to the winding shaft 5 
and perpendicularly to the guide vanes 8. The jet nozzles 13 are closed 
off by plugs or rupture discs, if the pullback device is not actuated, 
which plugs are not shown in the drawings. The receptacle 9 further has a 
liquid chamber 14 which extends in the radial direction, is filled with a 
liquid buffer and is constricted at the center by an inner extension 15. 
The screw cap 10 is screwed to the free cup rim of the receptacle 9 and 
has a hole 16 in a cup-shaped extension. The hole 16 can be closed off by 
a rupture disc 18 provided with a sealing ring 17. The coupling ring 11 is 
screwed onto a cylindrical threaded extension 19. The coupling ring 11 has 
an axial opening 20 as well as an insulating ring 21 which is placed on 
the circumferential surface of ring 11 and on which two slip rings 22 of 
an ignition contact device are mounted. The stationary ignition contact 
device has a terminal 23 with ignition lines 24 as well as suitably 
spring-loaded brushes 25. A tubular displacement element 26 is guided on 
the radial shoulders of the receptacle 9 and the screw cap 10. Element 26 
is designed as a flat spiral spring having several turns covering the 
constricted part of the liquid chamber 14. 
As shown in FIG. 3, a displacement element 27 may also be constructed as a 
tube formed of mechanically easily deformable sheetmetal material. 
Displacement element 27 is provided with several folded ribs 28 that can 
be expanded by the explosive pressure coming from the center, and take the 
shape indicated by the dash-dotted lines. 
In the event of danger, i.e., if a given acceleration moment occurs, the 
ignition contact device is fired in a manner not described in detail. If 
the propellant charge contained in the interior of the threaded extension 
19 of the screw cap 10 is ignited, the explosive pressure breaks the 
rupture disc 18 and the compressed gas flows into the liquid chamber 14. 
In order to prevent an undesirable breakthrough of the gas pressure wave 
directly onto the jet nozzles 13, the displacement element 26 or 27 is 
provided which is expanded radially by the explosion pressure until it 
rests against the inside surface of the cup rim and thus acts like a 
pressure piston on the liquid buffer. Under the action of the liquid 
pressure, the plugs are pushed out of the jet nozzles 13 and the liquid of 
the liquid buffer is thrown essentially tangentially to the winding shaft 
at high speed against the guide vanes 8 of the guide ring 7 with the 
result that a large torque is imparted on the structural unit 9/10/11 
coupled with the winding shaft 5. The liquid can run off freely laterally 
to the guide ring 7. The mentioned torque causes a tightening of the 
safety belt 6 around the body of the vehicle passenger to be protected.