WO1997019838A1

WO1997019838A1 - Safety belt retractor

Info

Publication number: WO1997019838A1
Application number: PCT/EP1996/005304
Authority: WO
Inventors: Martin Specht
Original assignee: Icsrd Rückhaltesysteme Für Fahrzeugsicherheit Gmbh
Priority date: 1995-11-30
Filing date: 1996-11-29
Publication date: 1997-06-05
Also published as: DE19544783A1

Abstract

A safety belt retractor having a winding shaft (1) for a safety belt webbing (20), a vehicle-sensitively and/or belt webbing-sensitively controllable blocking device (2) for the winding shaft (1) and a force limiter (3), which is operative after the blocking device is actuated, for a limited belt webbing extension, which has a plurality of force limitation steps along the limited belt webbing extension, of which steps the first step which is operative at the beginning of the limited belt webbing extension is limited to a higher belt extension force than the second step which is operative in relation to the subsequent belt webbing extension length.

Description

Safety belt retractor

The invention concerns a safety belt retractor having a winddLng shaft for a safety belt webbing, a blocking device which is controllable sensitively in relation to the vehicle and/or the belt webbing, for the winding shaft, and a force limiter which is operative after the blocking device is actuated, for limited belt webbing extension.

A safety belt retractor of that kind is described in German patent application No P 44 26 479.8. The force limiter which comes into operation after blocking of the winding shaft reduces the deceleration forces which act on the belted-up vehicle occupant when the occupant falls into the safety belt which is blocked to prevent extension of the belt webbing. The force limiter permits a limited belt webbing extension effect when belt webbing extension forces which are set by the force limiter are exerted by the vehicle occupant falling into the belt webbing. As an essential component, the force limiter includes a deformable element at which deformation work is done by the force applied by the body of the vehicle occupant, falling into the safety belt, during limited extension of the belt webbing. Relatively high loadings still act on the body of the vehicle occupant, during the limited belt webbing extension effect.

The object of the present invention is to provide a safety belt retractor of the kind set forth in the opening part of this specification, in which, to improve the degree of comfort involved, the body of the vehicle occupant is exposed to a reduced loading during the limited belt webbing extension effect.

According to the invention that object is attained in that, along the limited belt webbing extension, the force limiter has a plurality of decreasing force limitation values and in particular force limitation steps, of which the first value which is operative at the beginning of the limited belt webbing extension is limited to a higher belt extension force than the values which are operative in relation to the subsequent belt webbing extension length, in particular the second step.

In that way the deformation work done by the vehicle occupant body falling into the safety belt, at the force limiter, during the available limited belt webbing extension, is reduced in comparison with known systems, in other words, the vehicle occupant is exposed to a reduced loading.

The invention can be used in a safety belt retractor in which the belt webbing has been tightened by a belt tensioner prior to blocking of the winding shaft. In that case the tightening drive of the belt tensioner can be transmitted to the belt webbing by way of the winding shaft.

Preferably the invention is used in combination with an air bag. As the air bag can catch forward movement of the vehicle occupant in the vehicle, forward movement of the vehicle occupant is permissible along a given belt webbing extension effect during which the force limiter is operative. In that case, co-operation with the air bag can be such that the second step which is operative in relation to a low belt extension force begins at the same time with triggering of the air bag.

After filling of the air bag, the retaining force can tend towards zero. The first force limitation step can be at about 5 kN and the second force limitation step can be at about 2 kN. Advantageously at least two force limiting devices are used in the force limiter, wherein the at least two force limiting devices are additively operative at the beginning of the limited belt webbing extension and at least one force limiting device goes into an inoperative condition after a given belt webbing extension length or after a given period of time which begins with blocking of the winding shaft has expired. That can occur from the exterior or by v-rtue of the fact that there is a desired-rupture location in the force limiting device for rendering inoperative the force limitation effect of the additive action of said device.

If the safety belt retractor is combined with an air bag that force limit.ing device can be rendered inoperative as a result of triggering of the air bag. In that case only the remaining force limiting device still operates, to a limited extent. If failure of air bag triggering occurs, this arrangement ensures that a restraining force is applied to the vehicle occupant by the blocked winding shaft under the effect of the first step of the force limiter.

The invention will be described in greater detail hereinafter by means of an embodiment with reference to the drawings in which: Figures 1 and IA are diagrammatic views of a safety belt retractor with a force limiter which is an embodiment of the invention, in its normal operation,

Figures 2 and 2A show the embodiment of Figure 1 after blocking of the winding shaft of the safety belt retractor as a result of excessive acceleration or deceleration of the vehicle in the first force limitation step,

Figures 3 and 3A show the embodiment in the second force limitation step, Figure 4 shows an embodiment of a force limiting device,

Figure 5 is a plan view of the force limiting device shown in Figure 4,

Figure 6 is a perspective view of the force limiting device shown in Figures 4 and 5, and Figure 7 shows a force diagram for the embodiment with limited belt webbing extension.

The safety belt retractor shown in Figures 1 to 3 has a winding shaft 1. The winding shaft 1 is rotatably mounted in a retractor frame 18 which is only diagrammatically illustrated. A blocking device 2, for example in the form of a blocking pawl, is actuated in known manner by sensitivity to the vehicle and/or the belt webbing. In that situation the blocking device 2 comes into blocking engagement for example with an external tooth arrangement 19 on the winding shaft 1. The vehicle- sensitive and/or belt webbing-sensitive device required for controlling the blocking device 2 is not shown in detail and can be disposed on the left-hand side of the construction shown n the drawings. Disposed on the right-hand side of the retractor frame 18 is a drive spring (not shown) which is force-lockingly and n particular rigidly connected to a coupling portion 17 in known manner by way of a spring core or heart- shaped portion. The coupling portion 17 is carried on a shaft 15 which passes through the winding shaft 1. The shaft 15 can be in the form of a spline shaft and the mode of operation thereof is described in detail hereinafter. In a crash situation, a belt tensioner drive can also be coupled to the coupling portion 17 in known manner. The illustrated embodiment has a force limiter 3 n the interior of the winding shaft 1. In the illustrated embodiment the force limiter 3 is formed by three force limiting devices 4, 5 and 6. As can be seen in particular from Figure 2 the force limiting devices 4 and 5 which are disposed on both sides of the central plane which passes perpendicularly through the axis of the winding shaft include deformation bodies 12 and 14. The deformation bodies 12 and 14 can be deformed by a deformation movement which occurs parallel to the axis of the winding shaft, as will be described in detail hereinafter. The force limiting device 6 is also provided in the centre of the winding shaft 1. The force limiting device 6 is formed by a deformable bush or sleeve 25, n particular in the form of a double deformation bush or sleeve. An embodiment is shown n Figures 4 to 6. It has two hard bodies 13, for example in the form of plates of hard metal, which bear against bevelled end surfaces 26 of the thrust elements 11. The two bodies 13 are n that way held between the two thrust elements 11. The sleeve 25 comprises a deformable material. Provided in the centre of the sleeve 25 is a propellant 27 which, as will be described hereinafter, can be fired by firing simultaneously with triggering of the air bag, and can be converted into a pressure gas. The force limiting device 6 can be put out of operation by that pressure gas.

The axial movement which transmits the deformation work to the deformation bodies 12, 13 and 14 is derived from a screwthread engagement and the rotary movement transmitted from the limitedly extended belt webbing 20 to a part of the winding shaft 1.

When for example n a crash situation the blocking device 2 engages into the external tooth arrangement 19 on the winding shaft 1, the winding shaft is blocked to prevent further rotary movement thereof. The body of the vehicle occupant, which falls into the safety belt webbing 20, applies a force acting in the belt extension direction, to the belt webbing and the winding shaft 1. The force limiter 3 is provided so that that force does not represent an excessive loading on the vehicle occupant. In addition to the deformation bodies 12, 14 and 25 in the three force limiting devices 4, 5 and 6 the force limiter 3 has thrust elements 11 which are provided on both sides of the central plane which is perpendicular to the axis of the winding shaft. The thrust elements 11 have left-hand and right-hand screwthreads 7 and 8 which co-operate with corresponding screwthreads at inside surfaces of a hollow- cylindrical winding shaft portion 9, for example the winding drum. By virtue of the forward displacement force which acts on the winding shaft portion 9 by way of the belt webbing 20, the winding shaft portion 9 can be rotated with respect to winding shaft portions 10 which are held fast on both sides of the blocking device 2 and which are locked to prevent rotary movement thereof, the winding shaft portions 10 being for example in the form of toothed discs at the ends, the toothed discs carrying the external tooth arrangements 19. Desired-rupture locations 21, 22, for example in the form of shear pins, can be severed between the winding shaft portion 9 and the winding shaft portions 10 which are prevented from rotating.

Upon rotation of the winding shaft portion 9, the screwthread engagement between the screwthreads 7, 8 on the thrust elements 11 and internal screwthreads 23 , 24 on the winding shaft portion 9 causes axial movement of the thrust elements towards each other. For that purpose the thrust elements 11 are prevented from rotating and are axially guided with respect to the winding shaft portions 10, in particular the toothed discs, which are locked to prevent rotary movement thereof. The shaft 15 passing therethrough forms a further guide means for the thrust elements 11. The shaft 15 can be in the form of a splined shaft or a polygonal shaft.

The deformation bodies 12 and 14 of the force limiting devices 4 and 5 are disposed between the two thrust elements 11 and the winding shaft portion (winding drum) 9 which is irtmobile in the axial direction. The deformation body 13 of the force limiting device 6 is disposed between the two thrust elements 11 which are movable towards each other. At their one sides the deformation bodies 13 of the deformation sleeve 25 are supported against the one thrust element 11 while on the other side they are supported against the other thrust element 11. Support is afforded at the inclined end surfaces 26 of the thrust elements 11.

The three force limiting devices 4, 5 and 6 are operative in the first force limitation step which is shown in Figures 2 and 2A. Upon displacement of the thrust elements 11 towards each other the deformation bodies 12, 14 and the deformation sleeve 25 are sirπultaneously deformed. In that case, in the force limiter 6, the hard metal plates 13 are pushed away from each other by virtue of the action of the inclined surfaces 26 and deform the sleeve 25. A belt webbing extension force of about 5 kN is required for that purpose. In the force diagram in Figure 7 that first step is operative approximately as far as a belt webbing extension length of about 35 m. That corresponds to a period of time of about 18 to 25 ms, beginning with blocking engagement. After that period of time or that belt webbing extension length, the force limiting device 6 is rendered inoperative for example by a desired-rupture location in the force limiting device 6 becoming effective or triggered by an air bag triggering signal due to destruction of the sleeve 25. It is also possible to provide desired- rupture locations at the place where the deformation bodies 13 are supported against the sleeve 25 for rendering inoperative the force limiting device 6, or similar means.

Figure 3 diagrammatically shows that a filling gas for an air bag 29 is produced by means of a firing device 28. Triggering of the a r bag can be used to fire the propellent composition 27 in the embodiment shown in Figures 4 to 6. The pressure gas which is produced in that situation results in destruction of the deformation sleeve 25 in the central force limiting device 6. The pressure gas could also be passed from an external fired gas generator through a central feed conduit through the shaft 15 to the force limiting device 6. After the force limiting device 6 has been cut out, only the two force limiting devices 4 and 5 are still operative. They form a force limiting step of about 2 kN and, as can be seen from Figure 7, are operative approximately as far as a belt webbing extension length of 105 mm which can correspond to a force limitation time of about 45 to 55 ms. At that time the air bag is fully deployed so that it can catch the forwardly displaced body of the vehicle occupant. There is then no longer any need for a restraining force to be exerted by the belt retractor. This is represented by the broken line showing the variation in force, that tends towards zero, in the diagram in Figure 7. It is however also possible for a rising restraining force to be exerted by the belt retractor when the two deformation bodies 12 and 14 are deformed as far as the end of their deformation capability and the two thrust elements 11 possibly come into contact at the centre. That is the situation which arises if the air bag is not triggered.

If a tensioner drive can be coupled to the coupling portion 17, the tensioner drive movement can be transmitted to the winding shaft 1 in a belt retraction direction by way of the coupling portion 17 and the shaft 15 which is rigidly connected thereto. When the tightening movement is transmitted to the winding shaft 1 the two thrust elements 11 are supported by virtue of their right-hand and left-hand screwthread engagement in the shaft portion (winding drum) which consists of one piece, and possibly also against abutments of the shaft 15, so that they cannot move outwardly away from each other. The tensioning movement is applied to the belt webbing 20 in the belt retraction direction prior to blocking of the winding shaft. Upon termination of the tensioning movement and when the winding shaft 1 is blocked, the force limitation effect occurs n the belt extension direction to produce the restraining force, which is shown in the diagram in Figure 7. Blocking of the tensioner drive in the belt extension direction can become operative by way of the coupling portion 17 and the shaft 15, on the thrust elements 11 and the winding shaft 1. When the belt retractor is combined with an air bag that blocking or locking effect in respect of the belt tensioner can also be decoupled from the coupling portion 17.

Claims

1. A safety belt retractor having a winding shaft for a safety belt webbing, a vehicle-sensitively and/or belt webbing-sensitively controllable blocking device for the winding shaft, and a force limiter which is operative after the blocking device is actuated, for limited belt webbing extension, characterisedin that the force limiter (3) has force limitation values which decrease along the limited belt webbing extension, of which values the value operative at the beginning of the limited belt webbing extension is limited to a higher belt extension force than the values operative in relation to the subsequent belt webbing extension.

2. A safety belt retractor according to claim 1 characterised in that there are provided at least two force limitation steps.

3. A safety belt retractor according to claim 1 or claim 2 characterised in that the force limiter (2) has at least two force limiting devices (4, 5, 6) which are additively operative at the beginning of the limited belt webbing extension and that at least one force limiting device (6) goes into an inoperative condition after a given belt webbing extension length.

4. A safety belt retractor according to one of claims 1 to 3 characterised in that the first force limitation step is about five kN and the second force limitation step is about two kN.

5. A safety belt retractor according to one of claims 1 to 4 characterised in that the at least one force limiting device (6) is put into the inoperative condition from the exterior.

6. A safety belt retractor according to one of claims 1 to 5 characterised in that the second force limiting step begins with triggering of an air bag.

7. A safety belt retractor according to one of claims 1 to 6 characterised in that the at least one force limiting device (6) is put into the inoperative condition by the triggering of the air bag.

8. A safety belt retractor according to one of claims 1 to 7 characterised in that the force limiting devices (4, 5, 6) have deformation bodies (12, 13, 14) which are deformable in the axial direction.

9. A safety belt retractor according to one of claims 1 to 8 characterised in that to produce the deformation movement there is provided at least one screwthread (7, 8) between a winding shaft portion (9) which is rotated n relation to the limited belt webbing extension and a winding shaft portion (10) which is locked to prevent rotary movement by the blocking device (2) .

10. A safety belt retractor according to claim 9 characterised in that at least one thrust element (11) is displaceable by screwthread engagement in the axial direction for deformation of the deformation bodies (12, 13, 14).

11. A safety belt retractor according to one of claims 1 to 10 characterised in that the thrust elements (11) are mounted displaceably in the axial direction on a shaft (15) which passes axially through the winding shaft (1) .

12. A safety belt retractor according to one of claims 1 to 11 characterised in that the thrust elements (11) are movable towards each other.

13. A safety belt retractor according to one of claims 1 to 12 characterised in that at least one deformation body (13) is arranged between the thrust elements (11). 14. A safety belt retractor according to one of claims 1 to 13 characterised in that at least one deformation body (12,

14) is arranged between the thrust elements (11) and at least one component (9) which is .uTmobile in the axial direction.

15. A safety belt retractor according to one of claims 1 to 14 characterised in that at least one force limiting device (6) is adapted to be destructible to form the at least second force limitation step.

16. A safety belt retractor according to claim 15 characterised in that the force limiting device (6) is destructible by a pressure gas which is produced as a result of air bag triggering.

17. A safety belt retractor according to claim 15 characterised in that the force limiting device (6) is destructible by a desired-rupture location.

18. A safety belt retractor according to one of claims 1 to 17 characterised in that after filling of the air bag the restraining force exerted on the belt webbing by the belt retractor goes towards zero.