[Fig. 80] shows an illustration of the Philbrin contact maker which operates in this manner. The cam A strikes against the end of the plunger B and forces the points together at C, and holds the contact for approximately three and one-half degrees of the revolution of the cam. The spark occurs simultaneously with the separation of the contact points. The contact maker has but one adjustment; that of the adjustable contact screw, which is in direct line with the contact plunger. The contact points are brought together gradually by the surface formation of the cam. When the point of ample saturation of the coil is reached, the breaking of the contacts is instantaneous. The duration of the spark is in proportion to the speed of the engine, but breaking of the points is always instantaneous and entirely independent of the engine’s speed thereby producing the required spark at all speeds without any spark lag.
Fig. 81. Philbrin Contact Maker and Distributor Blade
[Fig. 81] shows the distributor blade mounted over the contact maker. The distributor blade is so arranged that it clears the spark plug lead terminals in the cover by a slight margin, and does not make actual contact, thereby eliminating all friction due to such contacts.
Operation.—Turning on the switch sets up a low tension current in the coil and primary wire coil when the contact points close. The sudden breaking of this current causes demagnetism of the core and the primary coil to set up a high tension current in the secondary coil. This current is led to the distributor blade and passes to the spark plug terminals as the blade comes in contact range.
The Philbrin high frequency system uses the same coil and distributor as the single spark system. But as the circuits of the two systems are entirely distinct and separate, they do not conflict with each other. The high frequency system has its own condenser and interrupter located in the switch case, and supplies a continuous flow of sparks.
Fig. 82. Switch Case
[Fig. 82] shows the interior of the switch case. This part of the mechanism controls the interruption of the battery current. The current is supplied to the interruptor through a polarity reverser, which reverses the direction of the current each time the switch button is turned. This equalizes the wear on the contact points.
Attention is again called to the distributor blade shown in [Fig. 82], which is used for both systems. Because of the shape of this blade, there is a continuous flow of sparks after the explosive spark has been delivered to one cylinder until the forward edge of the distributor blade is within range of the distributing point of the next terminal. By this action the first spark delivered to the cylinder is an efficient one, and the follow up continues at intervals of approximately one-thousandth of a second. These sparks are all perfectly synchronous.