Acceleration Sensor

Abstract

A holding mechanism for a vehicular acceleration sensor, comprising: a pair of lever arms operable to move independently of one another; and an inertia weight held between the lever arms, wherein movement of the inertia weight, in use, when under acceleration, causes at least a part of at least one lever arm or both arms to move in a generally linear direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of an inertia reel incorporating a sensor embodying the present invention;

FIG. 2 is a cross section through the inertia reel of FIG. 1;

FIG. 3 is an exploded view of the inertia reel of FIG. 1;

FIG. 4 is a partial perspective view of a strap acceleration sub-assembly for use with the reel of FIG. 1;

FIG. 5 is a perspective view of a sub-assembly of an acceleration sensor embodying the present invention.

FIG. 6 is a perspective view of the sub-assembly of FIG. 3 together with a trip plate;

FIGS. 7, 8 and 9 are perspective views showing the operation of the trip plate of FIG. 6;

FIGS. 10 and 11 show detail of a cam plate, pawl and trigger for use with the acceleration sensor embodying the present invention;

FIGS. 12A and 12B show the cam plate, pawl and trigger of FIGS. 10 and 11 when reset, prior to triggering;

FIGS. 13A and 13B show the cam plate, pawl and trigger of FIGS. 10 and 11 after triggering;

FIGS. 14 and 15 show manual operation of the cam plate of FIGS. 10 and 11.

FIG. 16 is a cross-section through a sensor sub-assembly embodying the present invention experiencing an on-axis acceleration;

FIG. 17 is a cross-section through the sub-assembly of FIG. 16 when experiencing an off-axis acceleration;

FIG. 18 is a sensor sub-assembly embodying another aspect of the present invention; and

FIG. 19 is the sensor sub-assembly of FIG. 18 experiencing an off-axis acceleration.

FIG. 20 shows a trip piston 86 of a sensor embodying the present invention.

FIG. 21 shows a pawl of a sensor embodying the present invention.

Claims

1. A holding mechanism for a vehicular acceleration sensor, comprising: a pair of lever arms operable to move independently of one another; and an inertia weight held between the lever arms, wherein movement of the inertia weight, in use, when under acceleration, causes at least a part of at least one lever arm or both arms to move in a generally linear direction.

2. A holding mechanism according to claim 1, wherein movement of the inertia weight, held between the lever arms, when under acceleration, causes one or both arms to move in a plane.

3. A holding mechanism according to claim 1, wherein the pair of lever arms each has a cup portion, which cup portions face one another and hold the inertia weight therebetween.

4. A holding mechanism according to claim 3, wherein the cup portions have substantially conical internal surfaces.

5. A holding mechanism according to claim 1, wherein the inertia weight comprises a ball.

6. A holding mechanism according to claim 1, wherein the inertia weight comprises a non-spherical shaped ball, having one axis of rotational symmetry.

7. A holding mechanism according to claim 6, wherein the inertia weight comprises a ball with an equatorial bulge.

8. A holding mechanism according to claim 1, wherein the inertia weight comprises a ball with a pair of opposed substantially conical protrusions.

9. An acceleration sensor comprising: a holding mechanism according to claim 1;a trip mechanism to convert linear movement of a part of the holding mechanism into a rotational movement of the trip mechanism, which rotational movement comprises an output of the sensor.

10. An acceleration sensor according to claim 9, wherein the trip mechanism has an axis of rotation and the holding mechanism is movable in a plane, the axis of rotation lying in the plane.

11. An acceleration sensor according to claim 9, wherein the extent of rotational movement is indicative of an acceleration experienced by the inertia weight.

12. An acceleration sensor according to claim 9, wherein the trip mechanism has a centre of gravity which lies substantially in the axis of rotation.

13. An omni-directional acceleration sensor according to claim 9, to provide an output in response to an acceleration of the inertia weight in any direction.

14. An inertia reel comprising: an acceleration sensor according to claim 9; anda spool

15. An inertia reel according to claim 14, wherein at least a part of the sensor is housed in a part of the spool.

16. An inertia reel according to claim 15, wherein the majority of the sensor is housed in the spool.

17. An inertia reel according to claim 14, wherein the reel also includes a strap acceleration sensor and the acceleration sensor is at least partly housed in the strap acceleration sensor.

18. An inertia reel according to claim 14, wherein the rotational movement trips a trigger to cause locking of the spool.

19. An inertia reel according to claim 18, wherein the trip mechanism is rotatably mounted to a cam mechanism which holds the trigger.

20. An inertia reel according to claim 19, wherein the trip mechanism is biased into a position by an elastic member interacting between the cam mechanism and the trip mechanism, the biasing force exerted by the elastic member being overcome by rotation of the trip mechanism under vehicular acceleration above a predetermined threshold.

21. An inertia reel according to claim 14, further comprising a strap acceleration sensor.

22. An inertia reel according to claim 21 having a common trigger tripped by actuation of either the vehicular acceleration sensor or the strap acceleration sensor.

23. An acceleration sensor comprising an inertia weight located toward one end of a lever arm which is movable in a generally linear direction in response to movement of the inertia weight, movement of the inertia weight or a part of the lever arm adjacent the inertia weight in a generally linear direction being converted to a rotational movement of a trip mechanism as an output of the sensor.

24. An acceleration sensor having an inertia weight and a rotational output, wherein the axis of rotation substantially passes through the inertia weight.

25. A method of sensing a vehicular acceleration above a predetermined threshold comprising: holding an inertia weight movable under acceleration;translating movement of the inertia weight into a substantially linear movement; andconverting the substantially linear movement into a rotational movement of a trip mechanism, wherein the extent of rotational movement is indicative of an acceleration experienced by the inertia weight.