Impact sensor

• US 5,028,750 A
• Filed: 10/23/1989
• Issued: 07/02/1991
• Est. Priority Date: 02/09/1988
• Status: Expired due to Fees

• Current Assignee: Alfons Woehrl, Hans Spies, Horst Laucht, Messerschmitt-Boelkow-Blohm GmbH (Mercedes-Benz Group AG)
• Original Assignee: Messerschmitt-Boelkow-Blohm GmbH (Mercedes-Benz Group AG)
• Inventors: Laucht, Horst, Woehrl, Alfons, Spies, Hans
• Primary Examiner(s): SCOTT, JAMES R
• Application Number:
  US07/427,087
• Time in Patent Office: 617 Days
• Field of Search: 200/61.45 R, 200/61.45 M, 200/61.53, 335/205
• US Class Current: 200/61.45M
• CPC Class Codes: H01H 35/145 operated by a particular acceleration-time function
• CPC Class Codes: H01H 35/147 the switch being of the reed switch type

Abstract

A magnetic impact sensor for motor vehicles with a safety system such as an airbag or belt tensioner for an occupant restraint system, has a circuit breaker arranged in an electrical trigger circuit of the safety system for inflating the airbag or tightening the belt by closing the trigger circuit in response to an acceleration or deceleration effective beyond a prescribed time duration. For this purpose a magnet in combination with specially shaped pole pieces forms two magnetic circuits the magnetic conductances of which are influenced by the position of a ferromagnetic ball that moves in response to an impact relative to the pole pieces to thereby open or close the circuit breaker. Normally, in the absence of an impact the ball is in a first position that keeps the circuit breaker open. When an impact occurs the ball moves into a second position to close the circuit breaker and thus the trigger circuit.

Claims

1. A magnetic impact sensor, comprising a sensor housing (6,7) a reed relay mounted in said sensor housing and having at least two reed contacts, magnet means (1) for operating said reed contacts, said magnet mean shaving a north pole (N) and a south pole (S), means operatively mounting said magnet means in said sensor housing ferromagnetic pole piece means (3, 3a, 3b, 3c;

4, 4a, 4b, 4c) for forming two magnetic circuits arranged in parallel to each other, a ferromagnetic mass (2) movable in response to an impact force in a free space (10) in said sensor housing, said ferromagnetic pole piece means forming said first magnetic circuit through a first magnetic path (N, 3, 3a;

4a, 4, S) and through said ferromagnetic mass (2) when the latter is in a rest position in said first magnetic path while an impact force is absent, said ferromagnetic pole piece means also forming said second magnetic circuit through a second magnetic path (N, 3, 3a, 3b, 3c;

4c, 4b, 4a, 4, S) and through said ferromagnetic mass (2) when the latter is in a displaced position in said second magnetic path while an impact force is effective, said at least two reed contacts being normally open and extending substantially perpendicularly to a movement direction of said ferromagnetic mass (2), said reed relay being positioned in said second magnetic path, so that said normally open reed contacts are closed when said impact force is effective and open when said ferromagnetic mass is in said rest position while an impact force is absent.

2. The magnetic impact sensor of claim 1, wherein said free space in said housing means has an approximately semicircular horizontal cross-section.

3. The magnetic impact sensor of claim 1, wherein said pole piece means comprise two slanted sections (3a, 4a) forming a seat for said ferromagnetic mass (2) in its rest position, and two spaced yoke plates (3c, 4c) forming a gap in which said ferromagnetic mass is received when said mass is displaced by an impact force.

4. A magnetic impact sensor, comprising a magnet (13) having a north pole (N) and a south pole (S) arranged in a common plane, a housing having a conical housing section (14) and a tubular housing section forming a seat (11) where said conical housing section merges into said tubular housing section, a ferromagnetic mass (2) normally resting on said seat in the absence of an impact force, said magnet (13) being mounted in said tubular housing section, so that said common plane of said north and south poles extends in parallel to a plane defined by said seat (11), a reed relay (5) also mounted in said tubular housing section, so that reed contacts of said reed relay extend substantially in parallel to said common plane of said north and south poles, whereby said reed contacts of said reed relay are normally held open as long as said ferromagnetic mass (2) rests on said seat, and wherein said reed contacts are closed when said ferromagnetic mass (2) is removed from said seat in response to an impact force.

5. The magnetic impact sensor of claim 4, wherein said conical housing section (14) encloses a free space in which said ferromagnetic mass (2) is movable in response to an impact force.

6. The magnetic impact sensor of claim 4, wherein said magnet (13) is located in said tubular housing section between said seat (11) and said reed relay.