Motor vehicle collision sensing device

Abstract

A motor vehicle collision sensing device for an air bag system comprises a fork-shaped support leaf made of a base portion and a pair of leg portions, and a roller mass rotatably supported by a rolled portion of the support leaf. When collision occurs, the roller mass is caused to roll on the support leaf because of the inertia, and an electric contact on the support leaf is brought into contact with a stationary electric contact disposed between the leg portions of the support leaf, whereby a collision sensing circuit is closed to energize a squib unit so that a safety air bag is instantaneously inflated. A breakdown detecting circuit is provided to detect breakdown of any part of the support leaf. The detecting circuit comprises first and second electric resistors connected to the leg portions, respectively, in parallel with each other. When any one of the leg portions and/or base portion is broken, combined resistance of the resistors is subject to variations, so that by monitoring variations of voltage across the breakdown detecting circuit, breakdown of the collision sensing device is monitored whatever the position of the breakdown of the support leaf is.