A Clever Scintilla Impulse Coupling
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n1HE new impulse coupling for magi netos which Scintilla, Ltd., 14, Clerkenwell Close, London, E.C.1; has introduced upon the British market is now available for all types of Scintilla apparatus and is a neat and soundly con
structed device. It consists of .three principal parts—namely,. the housing, which is secured to the magneto end plate ; the driving member, which is suitable for any kind . of. Scintilla coupling; and the driven member, which is secured to the magiaeth Spindle by a key and a lock-nut.' The driving and driven member are interconnected by a strong double-coil spring: The driven member carries two balance weights, each of which has a pawl on the unweighted side of its fulcrum.
When the magneto is being driven at a slow rate of rotation, up to 110155 r.p.m., according to the model, gravity causes each balance weight in turn to hang inward at the top of its cycle, which means that its pawl projects outward and engages with a recessin the' housing. This prevents the driven member and magneto spindle from rotating, and instead the coil spring, is wound, storing a certain
1;34 amount of energy. After travelling through.a carefully determined arc, however, a cam on the driving member engages with the pawl, pressing it inwards and free from the recess in the housing. The spring is released and gives a sudden impulse to the magneto spindle, causing a powerful spark to be generated.
Immediately the engine accelerates to beyond the critical speed (this being easily and accurately determined in manufacture by the size of lightening holes drilled in the balance weights) centrifugal force keeps the balance weights extended so that the pawls cannot engage, the drive being then positively transmitted through the spring. To allow gravity to work the recess in the housing must be above the centre line and its position can be adjusted at the time of fitting. The relative positions of the driven member and magneto spindle, also, are decided by a choice of keyways, according to the model of magneto being mounted.