Before fully electronic ignitions were introduced, the ignition time was shifted by a mechanical or pneumatic ignition adjustment in the direction of 'early' depending on a rising load or increasing revs.
|Part load advance, because the mixture burns more slowly.|
How it works
The centrifugal advance device in the lower part of the distributor twists either the breaker cam, segment rotor
(Hall-effect pulse generator) or star (inductive pickup) with rising engine speed against the axle drive shaft in rotation direction. In addition, the ignition can be shifted forward, e.g., by pressing the accelerator pedal,
adjusting the vacuum controller.
In a restriction near the throttle valve the inlet manifold pressure drops and pulls the diaphragm to the right (left figure). Thus, the plate with the interrupter contact, the Hall-IC or the coils in the inductive pickup are
thereby moved against the rotation direction of the distributor shaft.
The vacuum adjustment and centrifugal force adjustment in combination can cause an advance of up to 45 °.