BUCKLE

Abstract: A buckle for a vehicle safety restraint, the buckle comprising a frame defining a passageway for receiving a tongue to be attached to the buckle, a latching member for engaging the tongue, the latching member being moveable between a tongue engaging position and a tongue disengaging position under action of a manually operable actuating member, an inertial member rotatably mounted substantially about its centre of gravity on the frame, the inertial member having an intermeshing means for co-operating with means on the actuating member for holding the actuating member against movement under high acceleration forces, the holding means inoperative on low acceleration manual actuation of the actuating member. The invention uses the property of a flywheel which enables it to be easily rotated at slow speeds, but is very hard to rotate if it is moving at high speed. Thus the force required to displace the actuating member (which is the buckle button) is proportional to the acceleration which the button experiences.

Description: BUCKLE DESCRIPTION The present invention relates to a buckle for a vehicle safety restraint and particularly to a pretensioner-proof buckle . The high inertial forces generated when a modern pretensioner is detonated have been known to cause spurious release of buckles with attendant safety implications. Some arrangements to pretensioner-proof buckles are known, for example from EP C 212 507 and EP 0 415 418, and US 5 115 543. It is an object of the present invention to provide an improved pretensioner-proof buckle arrangement. According to the present invention there is provided a buckle for a vehicle safety restraint, the buckle comprising a frame defining a passageway for receiving a tongue to be attached to the buckle, a latching member for engaging the tongue, the latching member being moveable between a tongue engaging position and a tongue disengaging position under action of a manually operable actuating member, an inertial member rotatably mounted substantially about its centre of gravity on the frame, the inertial member having an intermeshing means for co-operating with means on the actuating member for holding the actuating member against movement under high acceleration forces, the holding means being inoperative on low acceleration manual actuation of the actuating member. In a preferred embodiment the holding means comprises a pawl on the inertial member and a co-operating recess on the actuating member, the pawl being fixed to the inertial member and coaxially rotatable therewith between a holding position in which the pawl engages the recess in the actuating member and a position in which the pawl is released from the recess so that the actuating member is not held and is free to move. Preferably the inertial member comprises a flywheel disc, and the pawl is mounted to the rotation axis of the disc and a resilient turning bias is provided by a coil spring with one end mounted to the disc at a point spaced from its centre, and the other end mounted to the frame. The flywheel is preferably mounted in the plane of the buckle . Alternatively the inertial member may be a rotational roller mass lying across the width of the buckle. The roller mass may hold the actuating member by co-operating teeth on both parts. The invention uses the property of a flywheel which enables it to be easily rotated it it is moving at a slow speed, but is very hard to rotate if it is moving at high speed, i.e. it requires a small force to move it at low acceleration rates but requires a very high force at high acceleration rates. Thus the force required to displace the actuating member (which is the buckle button) is proportional to the acceleration which the button experiences . Thus when the button is manually depressed the flywheel moves easily and the buckle can be disengaged. However under the high acceleration levels experienced during pretensioning, typically 10,000 g, far more force is needed to rotate the flywheel and thus the button is blocked and the buckle prevented from disengaging. The invention has the particular advantage that the button is blocked under high acceleration forces in both directions so is secured both during a pretensioning stroke (acceleration phase) and at the end of the stroke (deceleration phase) . The invention will be more fully understood from the accompanying drawings which illustrate the invention by way of example and in which: Figure 1 is a schematic perspective view of a first embodiment of the present invention. Figures 2 and 3 are schematic plan views in more detail of part of the embodiment of Figure 1. Figure 4 is a schematic perspective view of a second embodiment of the present invention. Figure 5 is a schematic perspective view of part of Figure . Figure 6 is a graph of a typical pretensioning pulse. The first embodiment shown in Figures 1 to 3 , uses a pawl and slot blocking feature. The second embodiment shown in Figures 4 and 5 uses a rack and pinion arrangement. In Figure 1 an actuating member or buckle button 1 is shown with rearwardly extending side arms 2 for engaging in the buckle frame or housing (not shown) to guide the button for longitudinal movement, under manual pressure, to release the buckle fastening. A third arm 3 extends rearwardly from the middle of the button. A flywheel 4 is mounted at its centre on a pin 5 attached to the buckle housing or frame. An off-centre pawl or cam 6 is connected to the pin 5 and sits in a notch 7 in the middle arm 3 on the button 1. Figures 2 and 3 show part of the button 1, together with the button arm 3 and the flywheel 4. Figure 2 illustrates the normal button condition, i.e. extended, when the buckle is locked. The cam 6 sits in notch or slot 7. A stop 8 for the cam 6 is provided on the frame. Also a spring 9 connects a point 10 on the frame to the cam 6 via rear cam extension 11. This provides a turning torque on the cam 6 and the flywheel 4, about the centre 12 of the flywheel. In Figure 3 the arrangement of parts during buckle opening is shown and like parts are denoted by like reference numerals . The button 1 is manually depressed to the right in the direction of arrow A, thus pushing notch 7 past the cam 6 and rotating the cam and thus the flywheel 4 in an anticlockwise direction against the bias of spring 9. Depression of the button 1 releases the buckle fastening in known manner and subsequently a return spring (not shown) returns the button to the extended position shown in Figure 2. Under pretensioning conditions high acceleration forces are felt by the button 1. At the end of the pretensioning stroke, the button tends to keep moving in the direction A (to the right in the Figures) and this is the buckle releasing direction. Under high acceleration forces however, the flywheel 4 has increased inertia and requires more force to turn it thus movement of the button is resisted. The force required to displace the button is proportional to the acceleration force which it experiences. So for example, a 6 gram button being accelerated at 10,000 G is equivalent to a force of about 590 N. In general the force needed to release a buckle with a button of mass m, under acceleration a is given by F = ma. Taking into account the effect of the flywheel with inertial mass (I) : F = ∑ ma F = mx + I θ r where x = 2 IT r = distance which will turn the flywheel through an angle θ radians and where r is the radius of rotation which here is the distance of the camming surface from the centre of the flywheel. Thus x = θ r F = mx + I θ r = mx + I ( x \ r 2 F = x / m + I \ I r 2 For normal button release, a typical acceleration would be 0.04m/s 2 . Without the flywheel this is equivalent to a release effort of F = ∑ (springs + friction + inertia) = 20 N. The inertia term here is given by: F = ma = 6 x 10' 3 x 0.04 (for a 6 gram button) F = 2.4 x 10' 4 N and this is trivial in comparison with the contribution of the springs and the friction. Even if the release acceleration under normal conditions is 100 times greater than used in this calculation then the flywheel only adds 0 . 02 N to the force needed . The inertia of the f lywheel is given by : I = P II R 4 t 2 p = density R = radius of wheel t = thickness of wheel For zinc with a density of 7,000kg/m 3 and a wheel of 5 mm radius and 15mm thickness with a camming surface radius r of 3 m . I = 7.000 x II x (5 x IP '3 ) 4 x 15 x IP '3 2 = 0.1 x 10 "6 kg m 2 I = and this is the inertia term for the flywheel. Therefore total force needed is the sum of the button mass and the inertia: F = x (6 x 10- 3 + 10 x 10' 3 ] F = x ' 16 • IP '3 Using lead, and a bigger flywheel: R = 8 mm t = 20mm p = 11 4,000kgm 3 F = x ( 6 x 10 "3 + 160 x lO" 3 ) F = 166 x ■ IQ "3 For the lead version it would be preferably to have gearing in the range 10.1 → 20.1 since this would halve or quarter the effective acceleration on the button. Figure 4 shows an embodiment with gear teeth 20 on the rear arms 21 of button 1 co-operating with toothed ends of a central spindle 22 of a roller 23, formed of a cylindrical mass. This roller 23 acts in a similar manner to the flywheel of Figures 1 to 3. The roller 23 may comprise a single cylindrical mass as shown in Figure 4 or alternatively comprise two masses spaced along the length of the spindle 22, as shown in Figure 5. The duration of a pretensioning pulse of 10,000 G is typically around 0.4 - 0.5 seconds since it typically takes 0.15 seconds to attain from zero a typical test speed of 400mm/min = 6.6mm/second (equivalent to 1mm movement) . The acceleration curve then typically bottoms out and then the pulse reverses as the button decelerates when the pretensioning stops. This is shown in Figure 6.

Claims: CLAIMS 1. A buckle for a vehicle safety restraint, the buckle comprising a frame defining a passageway for receiving a tongue to be attached to the buckle, a latching member for engaging the tongue, the latching member being moveable between a tongue engaging position and a tongue disengaging position under action of a manually operable actuating member, an inertial member rotatably mounted substantially about its centre of gravity on the frame, the inertial member having an intermeshing means for cooperating with means on the actuating member for holding the actuating member against movement under high acceleration forces, the holding means being inoperative on low acceleration manual actuation of the actuating member. 2. A buckle according to claim 1 wherein the intermeshing means are located between the centre and the outer circumference of the inertial member. 3. A buckle according to claim 2 wherein the intermeshing means are located close to the centre of the inertial member. 4. A buckle according to claim 1, 2 or 3 wherein the holding means comprises a pawl on the inertial member and a co-operating recess on the actuating member, the pawl being fixed to the inertial member and co-axially rotatable therewith and operable to engage the recess in the actuating member thereby to effect a reverse transfer of the inertia of the inertial member to the actuator member. 5. A buckle according to any preceding claim wherein the inertial member is provided with a resilient turning bias into the holding position of the pawl in the recess. 6. A buckle according to any preceding claim wherein the inertial member comprises a flywheel disc and the pawl is mounted to the rotation axis of the disc and the resilient turning bias is provided by a coil spring, one end of which is mounted to the disc at a point spaced from its centre and the other end of which is mounted to the frame. 7. A buckle according to claim 1 wherein the holding means comprises an inertial roller mass rotationally mounted and fixed relative to the frame. 8. A buckle according to claim 7 comprising two inertial roller masses spaced apart across the width of the buckle . 9. A buckle according to claim 7 or 8 wherein the roller mass interacts with the actuating member via cooperating teeth on each.

Inventors: BURKE DAVID, GORDON IAN ALEXANDER, SMITHSON ALAN GEORGE, BURKE, DAVID, GORDON, IAN, ALEXANDER, SMITHSON, ALAN, GEORGE
Applicants: ALLIEDSIGNAL LTD, BURKE DAVID, GORDON IAN ALEXANDER, SMITHSON ALAN GEORGE, ALLIEDSIGNAL LIMITED, BURKE, DAVID, GORDON, IAN, ALEXANDER, SMITHSON, ALAN, GEORGE
Application year: 1997
Main classification: A44B11
IPC codes: A44B11