Magnetically biased velocity change sensor (4329549)

Inventors:
David S. Breed
Company:
Breed Corporation
Issued Date:
1982-05-11
Tags:
inactive position, operating position, biasing force

Abstract

A velocity change sensor comprises a body having a passage within which is a movable sensing mass normally maintained in an inactive position by a magnetic biasing force, but which is movable from its inactive position to an operating position in response to acceleration exceeding the biasing force. Movement of the mass is fluid damped to delay its movement to the operating position for a period of time during which the acceleration must exceed the biasing force. [USPTO]

Claims

I claim:

1. In a sensor construction adapted for mounting on a vehicle or the like having an instrumentality to be operated in response to acceleration of said vehicle above a predetermined threshold, said sensor having a body provided with a tubular passage containing a fluid, a magnetically permeable sensing mass within said passage movable in response to acceleration of said vehicle from an initial position toward a second position in which said sensing mass initiates operation of said instrumentality, there being a clearance between said passage and said sensing mass of such size as to enable said fluid to damp movement of said sensing mass, the improvement comprising magnetic means exerting a predetermined magnetic bias force on said sensing mass and restraining movement of the latter from said initial position until said bias force is overcome by acceleration whereupon said sensing mass is movable relatively to said body toward said second position, said magnetic means being of such capacity as to continue to exert on said sensing mass a magnetic force of decreasing magnitude as said sensing mass moves toward its second position, the magnetic force exerted by said magnetic means on said sensing mass being sufficient to return the latter to said initial position from any other position short of said second position.

2. A sensor construction according to claim 1 wherein said fluid is a gas.

3. A sensor construction according to claim 2 wherein said gas is air.

4. A sensor construction according to claim 1 wherein one end of said passage is closed and wherein the initial position of said sensing mass is adjacent said closed end of said passage.

5. A sensor construction according to claim 1 wherein said sensing mass is spherical.

6. A sensor according to claim 5 wherein said passage is of such length that as said sensing mass reaches said second position more than one half of said sensing mass has emerged from said passage.

7. A sensor construction according to claim 1 including actuating means adapted for connection to said instrumentality and extending into the path of movement of said sensing mass toward said second position for engagement by said sensing mass in response to movement of the latter a predetermined distance from its initial position.

8. A sensor construction according to claim 7 wherein said actuating means comprises electrically conductive, normally open switch means engageable by said sensing mass.

9. A sensor construction according to claim 8 wherein said sensing mass is formed of electrically conductive material.

10. A sensor construction according to claim 9 wherein said switch means includes spaced apart contacts, the spacing between said contacts being less than the corresponding dimension of said sensing mass.

11. A sensor construction according to claim 1 wherein said magnetic means comprises an annular magnet.

12. In a sensor construction of the kind having a body provided with a tubular passage containing a fluid and within which a magnetically permeable sensing mass is movable in one direction from an initial position toward a second position in response to acceleration of said body above a predetermined threshold in the opposite direction, there being a clearance between said passage and said sensing mass of such size as to enable said fluid to damp movement of said sensing mass, the improvement comprising magnetic means constantly exerting on said sensing mass a magnetic bias force, said bias force being of such magnitude when said sensing mass is in said initial position as to restrain movement of said sensing mass from said initial position until said bias force is overcome by a force due to acceleration whereupon said sensing mass is movable relatively to said body toward said second position as long as the force due to acceleration exceeds the magnetic force exerted on said sensing mass, said bias force being of such magnitude as to effect return of said sensing mass to said initial position from any other position short of said second position.

13. A construction according to claim 12 wherein said bias force is not more than about 5 Gs.

14. A construction according to claim 12 wherein said bias force is about 2 Gs.

15. A construction according to claim 12 wherein the distance between said initial and second positions is such that when said sensing mass occupies said second position said bias force is about 1 G.

16. A construction according to claim 12 wherein said magnet is annular.

17. A construction according to claim 12 wherein said magnet has an opening therein substantially in alignment with said passage.

18. A construction according to claim 12 wherein said clearance is of such size that fluid flow therethrough is substantially viscous.

19. A construction according to claim 12 wherein said one end of said passage is closed.

20. A velocity change sensor construction comprising a body having therein a passage containing fluid; a magnetically permeable sensing mass movably accommodated in said passage, the relative sizes of said mass and said passage establishing therebetween a clearance of such size as to restrict fluid flow therethrough and damp movement of said mass; and a magnet carried by said body and exerting on said sensing mass an initial bias force of such magnitude as to maintain said sensing mass in an initial position at one end of said passage until said mass is subjected to another force due to acceleration in excess of such bias force and in a direction toward said one end of said passage whereupon said sensing mass is enabled to move from said initial position toward a second position adjacent the opposite end of said passage, the bias force exerted by said magnet on said sensing mass diminishing as the latter moves toward said second position but being of such magnitude as to return said mass to said initial position from any other position short of said second position.

21. An acceleration sensor comprising a body having a passage therein; magnetic biasing means carried by said body adjacent but spaced from one end of said passage; and a magnetically permeable sensing mass positioned within said passage for movement in one direction along a path from a first position at said end of said passage to a second position further spaced from said biasing means and in response to acceleration above a predetermined threshold of said body in the opposite direction, said biasing means constantly exerting a magnetic force on said sensing mass opposing movement of the latter from said first position toward said second position, the strength of said magnetic means, the spacing between said magnetic means and said first position, the weight of said mass, and the length of said path between said first and second positions being so related that the magnetic force exerted on said sensing mass when the latter is in said first position is between about 2 to 5 Gs and the magnetic force exerted on said sensing mass when the latter is in said second position is about 1 G.

22. A sensor according to claim 21 wherein the magnetic force exerted on said sensing mass when the latter is in said first position is about 3 Gs.

23. A sensor according to claim 21 wherein the magnetic force exerted on said sensing mass when the latter is in said first position is about 2 Gs.

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