GB2157152A

GB2157152A - Safety belt tensioner

Info

Publication number: GB2157152A
Application number: GB08508752A
Authority: GB
Inventors: Hans-Hellmut Ernst
Original assignee: Britax Kolb GmbH and Co
Current assignee: Britax Kolb GmbH and Co
Priority date: 1984-04-10
Filing date: 1985-04-03
Publication date: 1985-10-23
Also published as: GB8508752D0; DE3413488A1; GB2157152B; DE3413488C2; JPS60259553A

Abstract

A safety belt tensioner for tensioning the shoulder belt of a vehicle safety belt in the event of an accident, comprises a piston 5 connected to a belt grip unit 2, an inertia sensor mass 11 and energy storage means. Trigger means 25 is arranged, when the sensor mass 11 is subject to acceleration exceeding a predetermined value, to release energy stored in the energy storage means so that the stored energy causes movement of the piston 5. Movement of the piston 5 then causes the belt grip unit 2 first to grip a vehicle safety belt 12 and then to apply tension to the belt 12 to tend to cause retraction thereof. <IMAGE>

Description

SPECIFICATION Safety belt tensioner The invention relates to a belt tensioner for tightening a seat belt round the body of an occupant in the event of an accident.

According to the invention, a safety belt tensioner for tensioning the shoulder belt of a vehicle safety belt in the event of an accident, comprises a piston connected to a belt grip unit, an inertia sensor mass, energy storage means, and trigger means arranged, when said sensor mass is subject to acceleration exceeding a predetermined value, to release energy stored in said energy storage means so that said stored energy causes movement of said piston and said movement of said piston causes said belt grip unit first to grip a vehicle safety belt and then to apply tension to said belt to tend to cause retraction thereof.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a transverse sectional view of a belt tensioning system in accordance with a first embodiment of the invention; Figure 2 is a transverse sectional view, on an enlarged scale, of the belt grip unit of the system shown in Figure 1; Figure 3 is a transverse sectional view, on an enlarged scale, of the retraction unit of the system shown in Figure 1; Figure 4 is a side view of the retraction unit shown in Figure 3; Figures 5a, 5b and x are scrap sectional views illustrating alternative constructions of part of the tripping mechanism of the retraction unit shown in Figures 3 and 4; Figures 7 and 8 show a component of the belt grip unit in more detail; Figure 9 is a sectional view taken on the line 9-9 in Figure 1;; Figure 10 is a transverse sectional view of a belt tensioning system in accordance with a second embodiment of the invention; Figures 11 and 12a are perspective views of alternative types of sensor mass for use in the system shown in Figure 10; Figure 12b is a side view of the sensor mass shown in Figure 12a; Figures 13 and 14 illustrate a modification to the sensor mass of Figures 12a and 12b; Figure 15 is a transverse sectional view of the retraction unit of a belt tensioning system in accordance with a third embodiment of the invention; Figure 16 is a transverse sectional view of part of the retraction unit of a belt tensioning system in accordance with a fourth embodiment of the invention; and Figures 17 to 19 illustrate part of the retraction unit of a belt tensioning system in accordance with a fifth embodiment of the invention.

Figure 1 shows the general layout of the retraction unit 1 and the belt grip unit 2 of a belt tensioning system in accordance with the invention.

The units 1 and 2 are fitted into a recess 7 of the Bpost 8 of a motor car in which the system installed.

The retraction unit 1 comprises a cylinder 10 of the belt tensioner 1 which is rigidly anchored to the back of the recess 7 by two fastenings 33 and 40. A piston rod 5 projects from the cylinder 10 and is connected, at its upper end, to a housing 9 forming part of grip unit 2. A safety belt 12 runs from a retractor reel 23 without touching the grip unit 2, to a conventional belt deflecting shoulder anchorage (not shown).

Figure 2 shows the grip unit 2 in more detail.

The housing 9 accommodates two clamping wedges 13 having teeth which face the belt and tapering outer faces 15 which abut against corresponding tapering inner faces 16 of the housing 9, their normal relative positions being determined by fixing lips 18 on the wedges 13 which are pressed into fixing slots 19 in the faces 16 by a spring 17.

The clamping wedges are 13 attached to respective straps 20 which have breakable reduced-width intermediate portions 21 and which are connected to a support 22 by suspension fastenings 34. The support 22 is fixed to the B-post 8 and includes a slide guide 24 on which the housing 9 is slidably mounter. The belt grip unit 2 is preferably made open-sided so as to allow the safety belt 12 to be inserted after it has been connected to its buckle, retractor and anchorages.

Figures 3 and 4 show the retraction unit 1 in more detail. A compression spring 3 is accommodated in the cylinder 10 and held in an almost fully stressed state by a bolt 25 which both connects it to the piston 4 and engages with two mutually aligned support points 28 on a sensor mass 11.

The sensor mass 11 is pivotally mounted on an axle 30 which is secured to the cylinder 10. When a specified deceleration (e.g. 89) in the direction of travel is exceeded, e.g. in a head-on collision, the inertial force 27 act on the centre of gravity 29 of the mass to pivot it forwards, freeing the bolt 28 which then rapidly slides along slots 31 in the walls of the cylinder 11, thus releasing the stored energy in the compression spring 3.

Reverting to Figure 2, when the sensor mass 11 releases the bolt 28, the piston rod 5 shoots down and pulls the housing 9 with it. The clamping wedges 13, which in the first instance are held in place by the straps 20 move towards each other because of the interaction of the tapered surfaces 15 and 16 and the teeth 14 engage the belt 12.

After a predetermined force, adequate to clamp the belt 12, has been exceeded, the breakable portions 21 of the straps 20 fail and the housing 12 is pulled down along the slide guide 24 by the piston rod 5, thus pulling the belt 12 downwards.

As can be seen from Figure 5a, the support point 28 comprises a bearing shell 35 which, like the bolt 25, is made of corrosion-resistant material, thus minimising variation of friction during the working life of the system. In a crash, the inertial force of the sensor mass 11 has to compress the spring 3 by an amount dependent on the depth a of the concave bearing shell 35. Depending on the power of the compression spring 3, the friction between the bolt 25 and the bearing shell 35, and the mass of the sensor mass 11, a given response threshold will require a given magnitude for a. For a small sensor mass 11, the concave bearing shell 35 may be replaced by a flat bearing shell 35a in which case the depth a is effectively zero (Figure 5b). The bearing pin 25 is replaced by a bearing pin 25a having a flat to engage with the bearing shell 35a.

Friction and the force of the compression spring alone determine the level of the response threshold.

As an alternative to the bearing shell, the support point 28 may comprise a rocker 36 (also made of corrosion- resistant material) as shown in Figure 6. The bearing pin 25 is replaced by a bearing pin 25b which includes a notch for receiving one end of the rocker 36, the other end engaging in a corresponding notch in the sensor mass 11. The force required to compress the spring 3 sufficiently to allow the rocker 36 to go over-centre from the position shown in Figure 6 so as to release the bearing pin 25b is determined by the angle B between the slot 31 and the radial line 30a from the pivot 30 to the axis of the bearing pin 25b.

Figures 7 and 8 show how the two clamping wedges 13, the two straps 20 and the spring 17 may be made as an integral plastic injection moulding.

Figure 9 illustrates how the recess 7 in the Bpost 8 accommodates most of the belt tensioner 1 and reduces the extent which it is necessary for the cover 37 to project into the passenger compart ment of the vehicle.

Figures 10 and 11 show an alternative form of the belt tensioner 1. For increased energy storage, a compression spring 3a has been provided of rectangular cross-section. Sensor mass 11a and lever 26 have been so designed that the former can pivot laterally as well as forwardly, with the result that the belt tensioner 1 is also actuated by sideways acceleration of the vehicle. As shown in Fig ure 11,the sensor mass 11a can pivot, on a bearing 30a, in a forward direction 27a, transverse directions 27b and 27c and intermediate directions having a forward component.The bolt 25 of Fig ures 1 to 9 is replaced by a lever 26 which is pivot ally mounted at one end and engaged at the other end by a single support point 28a on a sensor mass 11 a. Thus only half the force of the compression spring is supported by the sensor mass 11a, thus enabling the weight of the sensor mass 11 to be reduced. When the sensor mass 11a disen gages, the lever 26 swings downwardly along a path 38, through a slot 31 b in the side wall of the cylinder 10, to the position shown in dotted lines, freeing the piston 4 which is connected to the grip unit 2 by a cable 6.

Figures 12a and 12b show an alternative sensor mass 11b, in which the support point 28b, centre of gravity 29 and pivot 30b are all on one line of action. Thus the kinematic response characteristic is the same in any direction between 27b, 27a and 27c. The support point 28b comprises a part-spher ical recess, giving a direction-independent re sponse characteristic. if a direction-dependent response characteristic is required, giving different response thresholds for head-on and sideways accelerations, the part-spherical concave recess 28b of Figures 12a and 12b may be replaced by a the concave recess 28c having one curvature, giving a depth a1, in the transverse direction and a different curvature, giving a depth a2, in the longitudinal direction, as shown in Figures 13 and 14.

Figure 15 shows a space-saving arrangement, in which the retraction unit 1 of a safety belt tensioner is mounted inside the B-post 8 with its piston cord 6 extending through a hole 39 in the Bpost inner wall 8a. The line of action of the cord 6 extends through the centre of clamping 32 of the belt grip unit 2, the housing 9 of which is thereby held in abutment with the B-post inner wall 8a, rendering unnecessary the provision of a slide guide 24 (Figure 1).

As an alternative, to using a spring, the retraction unit may employ a pyrotechnic charge 44 housed in a cylinder 10b, as shown in Figure 16. A sensor mass 11c, carrying a firing pin 42, is mounted so as to be slidable in the direction of travel 27 of the vehicle against a sensor spring 41.

When a predetermined deceleration is exceeded, the inertia of the sensor mass 1c overcomes the spring 41 and the firing pin 42 detonates a percussion detonator 43 which fires the pyrotechnic charge 44, causing a piston 4b to pull down a piston rod 5b which is connected to the housing 9 of a belt grip unit as shown in Figure 2. The use of a percussion detonator enables the system to be self-contained, avoiding the need for an electric power supply. This arrangement is particularly suitable for use where a very fast response time is required (e.g. mini cars) or where greater retraction forces are desirable than can be achieved with a spring.

Where the retraction force is produced by a spring, the weight of the sensor mass can be reduced by using a pyrotechnic charge to trip the spring. Figures 17 to 19 show such a tripping device applied to a retraction unit 1c of the type disclosed in Figure 10, having a spring 3c housed in a cylinder 10c and acting on a piston 4e which is connected to a belt grip unit by a piston rod 5c.

The spring 3c is held in a compressed condition by a lever 26c. An explosive bolt 45 has a head 46 separated from its body 47 by a reduced-width breakable portion 48 which engages in a hole in the end of the lever 26c opposite to its pivot 49, thus retaining it in the position in which it holds a spring 3c in a compressed condition. As shown in Figure 19, the bolt 45 comprises a sensor mass 50, carrying a firing pin 51, mounted so as to be slidable in the direction of travel 27 of the vehicle against a sensor spring 52. When a predetermined deceleration (e.g. 89) is exceeded, the firing pin 51 hits a percussion detonator 53 with adequate force to fire a pyrotechnic propellant 54, fracturing the breakable portion 48 and thereby detaching the head 46 from the body 47 of the bolt 45. The lever 26c then swings downwardly, through a slot 55 in the side wall of the cylinder 10, freeing the piston 4c.

In any of the foregoing embodiments, the piston rod may be replaced by a cable and vice versa.

Claims

1. A safety belt tensioner for tensioning the shoulder belt of a vehicle safety belt in the event of an accident, comprising a piston connected to a belt grip unit, an inertia sensor mass, energy storage means, and trigger means arranged, when said sensor mass is subject to acceleration exceeding a predetermined value, to release energy stored in said energy storage means so that said stored energy causes movement of said piston and said movement of said piston causes said belt grip unit first to grip a vehicle safety belt and then to apply tension to said belt to tend to cause retraction thereof.

2. A safety belt tensioner according to claim 1, wherein the belt grip unit, comprises two clamping wedges located within a housing having tapering inner surfaces and resiliently biassed apart so as not to touch the belt prior to actuation of said trigger means, the housing being mounted for linear movement in the belt retraction direction and connected to the piston, and the two clamping wedges being connected to a fixed mounting support by straps adapted to break under a predetermined load.

3. A safety belt tensioner according to claim 2, wherein the clamping wedges and the spring are a one-piece plastics moulding.

4. A safety belt tensioner according to claim 2 or 3, wherein the housing is mounted on a track secured to the fixed support mounting.

5. A safety belt tensioner according to any preceding claim, wherein the energy storage means comprises a compression spring.

6. A safety belt tensioner according to claim 5, wherein the means determining the predetermined acceleration to which the trigger means responds comprises means for applying a further compression to said spring during initial movement of said sensor mass.

7. A safety belt tensioner according to claim 6, wherein the sensor mass is movable in more than one direction and means for applying a further compression is arranged to apply a greater further compression when the sensor mass moves in one direction than that applied when the sensor mass moves in another direction.

8. A safety belt tensioner according to claim 5, 6, or 7, wherein the sensor mass is pivotally mounted and the point of its engagement with the trigger means, its centre of gravity and its pivotal mounting are all located on one line of action.

9. A safety belt tensioner according to claim 5, wherein the trigger means comprises an explosive bolt having a percussion detonator and a trigger spring arranged to prevent engagement of the sensor mass with the detonator until said sensor mass is subject to an accelleration exceeding said threshold value.

10. A safety belt tensioner according to any of claims 1 to 4, wherein the energy storage means comprises a pyrotechnic charge and the trigger means comprises a percussion detonator and a trigger spring arranged to prevent engagement of the sensor mass with the detonator until said sensor mass is subject to an accelleration exceeding said threshold value.

11. A safety belt tensioner for tensioning the shoulder belt of a vehicle safety belt in the event of an accident, substantially as hereinbefore described with reference to the accompanying drawings.