IGNITION ADVANCE MECHANISMS
( Centrifugal advance mechanism )- There are two general methods used in modern engines to advance and retard the ignition timing automatically in relation to engine speed and operating conditions after the initial timing is set manually, most manufacturers call these methods as automatic advance mechanisms :
- Centrifugal advance mechanism.
- Vacuum advance mechanism.
Centrifugal Advance Mechanism
It consists of two flyweights (advance weights), cam, spring and base plate. The flyweights are carried by the distributor drive shaft through the base plate which is fixed to the drive shaft. The flyweights are pivoted on the base plate and attached to the cam through springs. The cam is connected with the distributor drive shaft through the springs, flywheel and base plate.
When the engine speed increases, the weights move out due to centrifugal force rotating the plate and cam in the anti-clockwise direction. This movement affects the desired advance. This timing of the spark varies from no advance at low speed to full advance at high speed.
‘In an ignition timer, centrifugal timing mechanism comprising 2 coaxial rotatable plates, 2 centrifugal weights associated thereupon, one weight being pivotally mounted on every plate, means that to increasingly advance one plate with regard to the opposite because the weights area unit moved outwardly, aspiring command lever fulcrum on one plate, an adjustment arm mounted on the opposite plate and engageable with said lever to maneuver it against the resistance of its spring because the weights area unit moved outwardly, means that to regulate the position of aforesaid adjustment arm to cause it to interact aforesaid lever at totally different distances from its pivot, thereby variable the ratio of the plate advance as compared to the speed of rotation, a sticking member on one plate, and an arm mounted on the opposite plate and adjustable into the trail of aforesaid sticking member to adjustably limit the most possible advance of 1 plate with regard to the other.
In a centrifugal advance mechanism, a drive member, a driven member coaxial with that, flyweights operable by force to advance the driven member with relevancy the drive member, means that to adjustably limit the maximum range of such advance, and independent means that to result a predetermined adjustment of the rate of advance as compared to the increase: in speed.