GB2313398A - Safety belt buckle with release button counterweight - Google Patents

Abstract

A safety belt buckle comprises a slidably mounted release button 10 coupled to a lockbar 9 for engaging an aperture 7 in a lockable tongue 6, and a counterweight 17, of equal mass to that of the button 10, connected to the button 10 by a linkage providing lost motion, ie a peg 18 which engages an L-shaped slot 21 in the button 10. The buckle is balanced and compensates for pretensioning forces in the button acceleration direction as well as in a button deceleration direction. An ejector 15 is provided to bias the tongue 6 out of passageway 5 in the buckle when lockbar 9 is disengaged by depression of button 10.

Description

BUCKLE DESCRIPTION.

The present invention relates to a buckle for a vehicle safety restraint seat belt and particularly to a buckle which is adapted to resist the high acceleration forces imposed on the system by a pretensioner.

Pretensioners are used in modern vehicles to rapidly take up slack in a seat belt at the start of a crash pulse.

In this way the vehicle occupant is more securely restrained and more correctly and safely positioned in the seat. This is required particularly when an airbag is fitted to put the occupant in the correct position for maximum effectiveness of the airbag. However pretensioners are also used in seat belt systems without airbags since they arrest forward movement of the occupant at an earlier stage of a crash.

A pretensioner may be attached to the buckle end of a belt or to the retractor end. At the buckle end the buckle mechanism is subjected to very large acceleration forces and tends to become unlatched, either by the forces generated as the pretensioner accelerates the buckle in a belt tightening direction, or by the deceleration forces as the buckle comes to a stop at the end of the pretensioning stroke.

Various attempts have been made to avoid spurious release of buckles under pretensioning conditions, including blocking mechanisms, and compensating mass arrangements.

Examples are described in EP 0212 507 which uses a counterweight to balance the inertia of the buckle release button and EP 0485 656 which uses a pivoting lever to block movement of the button in a release direction under pretensioning conditions.

However problems are encountered with the known systems. Mechanical blocking systems are unreliable at very high pretensioning forces because the high forces can cause physically interacting parts to break or shatter thus disabling the buckle altogether. The known counterweight systems are bulky and also only compensate the button inertia in one direction, usually the deceleration direction at the end of the pretensioning stroke. With high power modern pretensioners these systems can fail at the beginning of the stroke, as the button is accelerating.

Thus the present invention aims to provide a pretensioner proof buckle which is more reliable than known buckles and which operates over the whole pretensioning cycle. It is also an object of the invention to provide a more compact buckle with a minimum number of parts, so as to be cost competitive.

According to the present invention there is provided a safety belt buckle for a vehicle safety restraint comprising a housing having a passageway for receiving a lockable tongue, a lockbar movable into and out of the passageway to engage and disengage the tongue, a release button slidably mounted in the housing, the button being operatively coupled to the lockbar for moving the lockbar between the engagement and disengagement positions, wherein a counterweight is mounted in the housing,, the mass of the counterweight being substantially equal to the mass of the button, and the counterweight being connected to the button by a linkage providing lost motion.

Preferably the counterweight has its centre of mass in line with the centre of mass of the button and this line is parallel to the line of insertion of the tongue in the passageway.

Preferably the lost motion linkage is formed by an L shaped slot in a longitudinally extending part of the button forming a cam surface which is engaged by a transversely extending peg attached to the counterweight. Advantageously L-shaped slots are provided on each longitudinally extending side portion of the button and corresponding pegs are provided on opposite sides of the counterweight.

In a preferred embodiment of the invention the release button incorporates overlocking means to hold the lockbar in the tongue engagement position. This may be by way of a cut out or recess in the side portion of the button providing at least one overlocking surface arranged to abut the lockbar to restrain it in a tongue engagement postion.

The lost motion linkage and the alignment of the centroids of the respective mass of the counterweight and of the button, allows for a very compact pretensioner proof buckle to be made. Around l0mm button travel is required in a preferred embodiment.

The counterweight may be formed in two parts of different materials so as to more accurately match the mass of the counterweight to the mass of the button. One of these is preferably zinc since zinc is easy to cast.

The buckle of this invention is a truly balanced buckle. In contrast to the prior art buckles, it compensates for pretensioning forces in a button acceleration direction as well as in a button deceleration direction. In the balanced state there are no moving parts during a pretensioning stroke and thus the buckle has a particularly long life and is less likely to be subject to mechanical failures during pretensioning operations.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made to the accompanying drawings in which: Figure 1 is a side cut-away view of a buckle according to the present invention.

Figures 2a and 2b are side and front views respectively of a counterweight used in the buckle of figure 1.

Figure 3 is a perspective view of the counterweight of figures 2a and 2b.

Figures 4 to 7 are sequence diagrams illustrating the operation of the buckle of figure 1 in side view.

Figures 8 to 11 are sequence diagrams of a part of the buckle of figure 1, shown in perspective view.

In the figures the buckle is shown comprising a housing 1 with a dust cover 2. The buckle is connected to a vehicle at end 3, for example to the vehicle floor by means of a cable or solid stalk. At the other end of the buckle is an opening 4 to a passageway 5 in which is located a locking tongue 6 which is attached to seat belt webbing to be fastened by the buckle. The tongue 6 has a hole 7, or may alternatively be of the well known T shape and have shoulders, to provide a locking surface 8 which abuts against a lockbar 9 to engage the tongue in the buckle. The lockbar 9 is biased into this engagement position by a leaf spring which is not shown but which presses on top of the lockbar 9. Of course, other suitable biasing means will be within the capabilities of anyone familiar with this field of technology.

The lockbar 9 is further held in the engagement position by an overlocking recess 23 at the lower end of ramp 12. This engages the shoulder 13 and prevents upward motion of the lockbar 9 unless the button is positively moved the direction of arrow 11.

The lockbar 9 is disengaged from the locking tongue by depression of a button 10 in the direction of arrow 11.

Movement of the button 10 in this direction moves integral ramp 12 which is formed by a cut out in the side of button 10. The ramp 12 engages a shoulder 13 extending from the lockbar through the side portions of the button. One such shoulder and one such ramp is provided at each side of the buckle. As the button 10 is depressed, the ramp 12 lifts shoulder 13 and thus lockbar 9 out of the hole 7 and thus out of engagement with the tongue 6. Once the angled face of the lockbar 6 is clear of the surface 8 then the tongue is free to move and is ejected from the passageway by an ejector 15 comprising a shaped forward member and a coil spring 16 biasing the forward member in the tongue ejection direction.

A counterweight 17 is coupled to the button 10 by an outwardly extending peg 18 engaging an L shaped slot 21 in the side of the buckle button 10.

The counterweight 17 is mounted to pivot about point 19 on a fixing pin 22 shown in figure 11 where the button is omitted for clarity.

The centre of gravity of the button 10 is aligned with the centre of gravity of the counterweight 17 in the direction of arrow 11.

Figure 2a shows a side view of the counterweight 17 and figure 2b shows a front view with transversely extending peg 18 and pivot axis 19 which is supported on the fixing pin 22 extending across the width of the buckle. Counterweights 17 are attached to each end of the fixing pin 22.

Alternatively a single counterweight may be used either extending across the width of the fixing pin or situated generally in the middle of the buckle.

The operation of the buckle will now be described with reference to figures 4 to 11.

The buckle in figure 4 is at rest with the tongue 6 locked by engagement with the lockbar 9 which is held in position by a leaf spring (not shown) and by cooperation of the lockbar shoulder 13 with button recess 23. This is the normal position for a buckle in use. In this position the buckle is subject to forces for example due to pretensioning operations and any reaction by the button to those forces will be exactly counterbalanced by the reaction of the counterweight 17. For example, if the button is accelerated in direction 11, the force on peg 18 will tend to turn the counterweight anticlockwise (arrow 25 in figure 8). However the force on the counterweight 17 is exactly opposite, tending to turn it clockwise.

Thus the forces tending to turn the counterweight 17, are exactly balanced and the buckle remains fastened. At the end of a pretensioning operation the button comes to rest and experiences a deceleration force in the direction 24, tending to turn the counterweight clockwise (arrow 26 in figure 8). This force will be counterbalanced by the force acting directly on the counterweight 17 tending to turn it anticlockwise.

In figures 5 to 7 the unlatching sequence is shown for normal operation of the buckle. The button 10 is pressed and because no acceleration forces are present the force is not countered by the inertia of the counterweight 17. Thus the button 10 moves in the direction of arrow 11, and with it moves the L shaped slot 21. Since counterweight peg 18 is in the vertical part of the slot 21, movement of the button causes a torque on the counterweight 17 about fixing pin 19 and counterweight 17 rotates anticlockwise (arrow 25). As it does so, the peg 18 travels up the vertical arm of the L-shaped slot 21 (figures 5 and 9) and subsequently along the horizontal arm (figures 6 and 10). This lost motion enables a more compact counterweight to be used and ensures that the pretensioner proof buckle fits into the same package size as the non-pretensioner proof buckle leading to considerable cost savings and more commercial convenience. In figure 9 the button has moved 3mm, in figure 10 6mm and in figure 11 the maximum 9mm travel is reached. Simultaneously the ramp surface 12 lifts the shoulders 13 of the lockbar 9 and raises it out of engagement with the tongue 6 allowing the ejector 15 to expel the tongue as shown in figure 7.

Claims (12)

1. A safety belt buckle for a vehicle safety restraint comprising a passageway for receiving a lockable tongue, a lockbar movable into and out of the passageway to engage and disengage the tongue, a release button slidably mounted for movement in the insertion direction of the tongue, the button being operatively coupled to the lockbar for moving the lockbar between the engagement and disengagement positions, wherein a counterweight is provided, the mass of the counterweight being substantially equal to the mass of the button, and the counterweight being connected to the button by a linkage providing lost motion.

2. A safety belt buckle according to claim 1 wherein the counterweight has its centre of mass substantially in line with the centre of mass of the button which line is parallel to the line of insertion of the tongue in the passageway.

3. A safety belt buckle according to any preceding claim wherein the lost motion linkage is formed by a cam on one of the button and the counterweight and a cooperating cam surface on the other of the button and the counterweight an L shaped slot forming a cam surface which is engaged by a transversely extending peg forming a cam.

4. A safety belt buckle according to claim 3 wherein the cam surface is formed by an L-shaped slot, and the cam is formed by a peg.

5. A safety belt buckle according to claim 4 wherein the L-shaped slot is formed in a longitudinally extending part of the button, and the peg is formed on the counterweight.

6. A safety belt buckle according to claim 5 wherein an Lshaped slot is provided on each of two longitudinally extending side portions of the button.

7. A safety belt buckle according to claim 6 comprising two independently mounted counterweights, one on each side of the buckle, each housing pegs extending outwardly in different directions to engage the corresponding L-shaped slots.

8. A safety belt buckle according to any preceding claim further comprising overlocking means for holding the lockbar in and being movable by the button to release the lockbar for movement to the disengagement position the tongue engagement position.

9. A safety belt buckle according to claim 8 wherein the overlocking means comprises a cut out or recess in a side portion of the button providing an overlocking surface arranged to abut the lockbar to restrain it in a tongue engagement position.

10. A safety belt buckle according to any preceding claim wherein the or each counterweight is formed in two parts of different materials.

11. A safety belt buckle according to claim 10 wherein the material of one part of the counterweight is cast zinc.

12. A safety belt buckle for a vehicle safety restraint substantially as hereinbefore described with the accompanying drawings.