US 6,550,306 B1Granted

Miniature acceleration sensor

AssigneeBreed Automotive Technology, Inc.

InventorMartyn Bensley

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Abstract

An upper housing is ultrasonically welded to a lower housing forming a hermetic seal about two opposed ferromagnetic leads extending from a reed switch. A shock sensing magnet has a cylindrical bore and is spring biased within the housing to slide along the glass capsule of the reed switch in response to acceleration. The magnet functions as a shock sensing mass, and is shaped to increase the reed switch dwell time. The reed switch leads are bent to extend downwardly along the sides of the housing and are bent horizontally to be parallel to the housing sides and a circuit board. A strip of mu-metal wraps three sides of the housing and has tabs extending partly beneath the housing for soldering to the circuit board. The magnet and the housing are constructed from plastics which can withstand momentary high temperature associated with a re-flow solder process.

Claims18

Dependent claims

A shock sensor comprising:

a housing;
a reed switch mounted to the housing having a first lead, and a second lead extending into a cylindrical glass capsule, the cylindrical glass capsule defining an axis and an outer cylindrical surface, the glass capsule having a first end sealed about the first lead, and a second end sealed about the second lead, the first lead forming a first reed, and the second lead forming a second reed, the first and second reed being hermetically sealed within the glass capsule, to form a magnetically activated switch;
a shock sensing magnetic mass having an interior bore through which the reed switch extends, the magnet in sliding engagement with the outer cylindrical surface of the glass capsule, the magnet movable by sliding along the outer cylindrical surface of the glass capsule from a first position to a second position at which the magnetically activated switch changes state;
a biasing member mounted to the housing between the shock sensing magnetic mass and a portion of the housing to bias the shock sensing magnetic mass in the first position, the biasing member allowing the shock sensing magnetic mass to move to the second position when the shock sensing magnetic mass experiences an acceleration having a component parallel to the defined axis which is sufficient to overcome the biasing member.

1 more element

A shock sensor comprising:

a housing having a back side, a top side, and a front side;
a reed switch mounted to the housing having a first lead and a second lead which extend into a cylindrical glass capsule, the cylindrical glass capsule defining an axis and having an outer cylindrical surface, the glass capsule having a first end sealed about the first lead, and a second end sealed about the second lead, the first lead forming a first reed and the second lead forming a second reed which are hermetically sealed within the glass capsule, to form a magnetically activated switch;
a shock sensing magnetic mass having an interior bore through which the reed switch extends, the magnet movable from a first position to a second position at which the magnetically activated switch changes state;
a biasing member mounted in the housing between the shock sensing magnetic mass and a portion of the housing, to bias the shock sensing magnetic mass in the first position, the biasing member allowing the shock sensing magnetic mass to move to the second position when the shock sensing magnetic mass experiences an acceleration having a component parallel to the defined axis which is sufficient to overcome the biasing member;
wherein the first lead and the second lead have a first bend of about 90 degrees so that a first portion of each lead extends axially away from the defined axis, and the first lead and the second lead have a second bend of about 90 degrees so that a second portion of the first lead and the second lead lie in a common plane, the second portion of the first lead and the second lead functioning as surface mount electrical contacts;
and
a metal foil wrapping the housing back side, the top side, and the front side, the metal foil providing tabs which extend beneath the housing for fixing the housing to a circuit board.

4 more elements

A shock sensor comprising:

a housing;
a reed switch mounted to the housing having a first lead, and a second lead extending into a cylindrical glass capsule, the cylindrical glass capsule defining an axis and having an outer cylindrical surface, the glass capsule having a first end sealed about the first lead, and a second end sealed about the second lead, the first lead forming a first reed, the second lead forming a second reed, the first reed and the second reed being hermetically sealed within the glass capsule, to form a magnetically activated switch;
a shock sensing magnetic mass having an interior bore through which the reed switch extends, the magnet movable from a first position to a second position at which the magnetically activated switch changes state;
a biasing member mounted in the housing, between the shock sensing magnetic mass and a portion of the housing to bias the shock sensing magnetic mass in the first position, the biasing member allowing the shock sensing magnetic mass to move to the second position when the shock sensing magnetic mass experiences an acceleration having a component parallel to the defined axis which is sufficient to overcome the biasing member;
and
a mu-metal shield positioned on the exterior of the housing to reduce the penetration of magnetic fields through the housing.

3 more elements

Dependencies are inferred from the claim text.