Page 115 - Vauxhall 20-60 H.P. (R Type) Chassis Shop Manual

VAUXHALL 20-60 SHOP MANUAL

In order to do this, it is necessary to pass current through the primary winding
of the coil from the lighting generator of the car. During starting up when
the lighting generator is not running this current is taken from the battery,
which has already been charged up by the generator when last the car was
in use. The necessary high voltage can only be produced in the secondary
winding when the current in the primary winding is suddenly stopped, a
steady flow of current in the primary having no effect whatever upon the
secondary. It is necessary, therefore, suddenly to break the primary current
at the exact moment at which a spark is required. This is done by means of
the contact breaker mechanism of the distributor which is shown in Fig. 32.

The distributor shaft which carries a 3-lobe cam, is driven at half-engine
speed, so that the points at each contact breaker are opened three times
in each revolution, that is to say there are in all six breaks every two
revolutions of the engine.

The distributor cap is provided on its inside with six metal inserts; these
are in contact with the high tension wires passing out of the side of the cap
and connected at the other end of the respective sparking plugs. The centre
lead which passes into this distributor cap is connected at one end to the
secondary winding of the coil, that is to say, the terminal at which the high
voltage is available, and at the other end by means of a spring contact to
the rotor.

The rotor is provided at its outer tip with a metal segment, which, when
the distributor cap is in position, passes very close to the inserts, although
it does not actually touch them.

The secondary voltage of the coil, however, is sufficiently high to jump
this gap, so that when the rotor is turned with the distributor shaft the
coil secondary terminal is virtually connected to the sparking plugs of each
cylinder in turn. It is necessary, therefore, to see that the sparking plugs are
connected up in such a way that the sparks occur in the various cylinders in
the correct sequence ( 1, 5, 3, 6, 2, 4 ).

The cycle of events therefore in the operation of the coil ignition system is
as follows:—

When the starter switch is depressed the distributor shaft rotates, the
contact breaker points will make and break alternately. This will give rise,
every time the points open, to a very high secondary voltage which will
be transmitted from the secondary terminal of the coil, through the high
tension cable to the distributor rotor, across the gap to the metal insert of
the distributor cap and thence by means of another length of high tension
cable to the sparking plug from which the spark is required.

As soon as the spark occurs, the contact breaker points will again close and
the cycle of operations will be repeated except that the spark will now occur
in the cylinder next in firing order.

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