Magnetostrictive engine detonation sensor

A vibration sensor adapted for use with a spark ignited internal combustion engine to detect ringing vibrations of a predetermined frequency due to engine knock, comprising, in combination:

• a generally cylindrical housing having opposing axial ends and being adapted at one of said axial ends for attachment to the engine for axial vibration therewith, the housing comprising a first resonant assembly having a first resonant frequency slightly higher than the predetermined frequency;
• magnetostrictive means comprising a plurality of parallel magnetostrictive rods compressed in stress axially between the opposing axial ends of the housing and a source of magnetic flux effective to establish a flux path axially through the rods, the flux path being characterized by a reluctance which varies with vibration-induced variations in stress within the rods;
• a pickup assembly comprising a spool and a pickup coil wound on the spool, the spool having an inner surface defining an axial opening therethrough and being disposed in the housing with the magnetostrictive rods extending through the axial opening, whereby the pickup coil is adapted to sense the vibration-induced reluctance variations in the rods and generate an output electrical signal therefrom, the spool further engaging the magnetostrictive rods along said surface in a force fit characterized by at least a predetermined push-out force, the spool surface in the vicinity of each rod conforming in shape to the rod for a substantial area of contact therebetween to spread the stress of the force fit in the spool, the pickup assembly thereby being physically coupled to the rods to form a second resonant assembly having a second resonant frequency slightly lower than the predetermined frequency, the first and second resonant assemblies in combination being effective to establish, in the sensor electrical signal output characteristic,
• a single resonant peak at substantially the predetermined frequency.

A vibration sensor adapted for use with a spark ignited, internal combustion engine to detect ringing vibrations due to engine knock, comprising, in combination:

• housing means having opposing axial ends and means on one of the axial ends for attachment to the engine for vibration therewith, the housing means comprising a first resonant assembly having a first resonant frequency slightly higher than the predetermined frequency;
• an elongated magnetostrictive element compressed longitudinally between the axial ends of the housing, the magnetostrictive element including a source of permanent magnetic flux in longitudinal orientation therethrough and defining, with the housing means, a flux path characterized by a reluctance which varies in response to vibration-induced variations in magnetostrictive element compression;
• a pickup assembly comprising a spool and a pickup coil wound on the spool, the spool having a surface defining an axial opening therethrough and being disposed in the housing with the magnetostrictive element extending through the axial opening, whereby the pickup coil is adapted to sense the vibration-induced reluctance changes in the magnetostrictive element and generate an electrical output signal therefrom, the spool further engaging the magnetostrictive element along said surface in a force fit characterized by a predetermined push-out force, whereby the pickup assembly is coupled physically to the magnetostrictive element to form a second resonant assembly having a second resonant frequency slightly lower than the predetermined frequency, the spool further having an electrical contact at one axial end thereof connected to the pickup coil;
• an electrical terminal member projecting through the housing means and being adapted, at one end within the housing means, to engage the spool electrical contact, whereby a conduit for the electrical output signal is provided to a point external of the housing means;
• and
• a spring axially disposed between the pickup assembly and one axial end of the housing, the spring exerting an axial force on the pickup assembly greater than the push-out force between the spool and magnetostrictive element, whereby the pickup assembly is automatically and permanently axially positioned with the spool electrical contact and terminal member in engagement while the coupling between the spool and magnetostrictive element is retained, the first and second resonant assemblies, in combination, being effective to establish an overall sensor electrical output signal characteristic with a single resonant peak at substantially the predetermined frequency.