External magnet flywheel mounting

Claim 1

A flywheel assembly for a small internal combustion engine of the type supporting a permanent magnet structure near the flywheel outer periphery for cooperating with a fixed ignition assembly and inducing spark creating voltages in the ignition assembly as the magnet structure rotates past the ignition assembly and comprising: a ferro-magnetic flywheel; a permanent magnet structure including a permanent magnet and a pair of flux transmitting pole shoes adjacent the respective poles of the permanent magnet, the poles of said magnet and the pole shoes circumferentially arranged near the periphery of said flywheel, each said pole shoe including a generally concave recessed portion in its outer peripheral surface circumferentially outwardly of said magnet, each said pole shoe further including a pair of shoulder portions along its radial inner peripheral surface adjacent said permanent magnet and forming a recess between said shoulder portions, said magnet disposed in said pole shoe recesses and restrained thereby from radial movement with respect to the axis of said flywheel; a substantially non-magnetic spacer axially positioned intermediate the flywheel and the permanent magnet structure for reducing flux leakage between the pole shoes by way of the flywheel, said spacer including a plurality of protuberances, said protuberances extending toward said pole shoes, each said protuberance cooperating with a respective said pole shoe concave recessed surface portion whereby said pole shoes are restrained from pivoting movement in a plane perpendicular to said flywheel axis; and a solid generally cylindrical fastener of substantially non-magnetic material passing through apertures in the magnet structure, spacer and flywheel, said fastener expanded radially in said apertures to tightly engage the magnet structure, spacer and flywheel.