« НазадПродовжити »
Fig. 194.-Views Showing Controlling Devices of 1916 Overland Car.
Note Controlling Switch on Steering Column and Starting Switch Button Next to Accelerator.
a-The generator which produces the current and delivers it to the lamps and storage battery.
b-The storage battery which accumulates the current thus generated and delivers it to the lighting system or the starting motor, as occasion demands.
C—The starting motor, which receives current from the storage battery and revolves the engine whenever it is to be set in motion.
Besides these three principal units the system includes the following auxiliary apparatus:
d-An automatic cutout, whose function is to disconnect the generator from the storage battery when the engine is stopped or running below the speed at which the generator's voltage is high enough to charge the battery. The cutout is located on the engine side of the dash.
e-The starting switch, which is a pedal-button located in the floor board of the car convenient to the foot of the operator.
f—The ammeter, whose purpose is to show whether the system is working properly or not. When the dynamo is running and sending current to the storage battery the ammeter hand will point to the right of zero or at “charge.” When the lights are burning or the starter motor is running, this hand will point to the left of zero or at “discharge,” thus indicating the rate at which current is going out of the storage battery.
The speed of the generator is controlled by an automatic clutch that is so designed that, no matter how fast the engine runs, the generator will not be driven faster than a certain predetermined speed which corresponds to that at which the engine runs when driving the car at 12 miles per hour on high gear, but, of course, if the engine drops below this speed the generator will also. This is done by means of a centrifugal governor which regulates the slippage of the clutch so that the generator cannot be driven faster than the predetermined speed, the greater the speed of the engine the more the clutch slips.
The current load is automatically taken care of by a compound winding on the generator. The starting motor is a series wound machine, that is, the entire armature current passes through the field. The motor is provided with an over-running clutch, which
Fig. 195.—Wiring Diagram to Show Arrangement of Parts of 1914 Overland-Gray & Davis Starting and
allows it to drive the engine but automatically disengages when the engine starts so that the engine will not drive the motor. If such a device were not fitted the generator might be injured by the motor driving it at too high a speed.
As already explained, the function of the automatic cutout is to disconnect the generator from the battery when the engine is stopped or turning so slowly that its voltage is below that of the battery. If this cutout were not provided the storage battery would discharge back into the generator.
The cutout consists of an electro-magnet with two windings. One is a shunt winding of many turns of fine wire and the other a series winding of a few turns of heavy wire, both windings being over a soft iron core. The shunt winding is permanently connected across the positive and negative terminals of the generator, so that when the generator comes up to charging speed, this winding energizes the magnet core and the magnet core attracts a steel arm that closes the circuit between the generator and the battery.
So long as the cutout points are closed the current must pass through the series winding of the cutout. This current adds its magnetizing influence to that of the shunt winding and holds the points together. The cutout is designed so that it closes at a carspeed of 12 miles per hour and opens at 10.
If, now, the speed of the generator drops below charging speed, the current begins to flow through the cutout series winding in the reverse direction. This weakens the pull and allows the points to fly apart, through the agency of a spring.
Now that a general idea of the different parts of the Gray & Davis system has been obtained, the path of the current in the different wires will be explained. The illustration shows this system with a very complete equipment. Besides the usual head, side and tail lights, there are pillar lights, dome lights, a speedometer light and an electric horn connection. It will be noticed that the return circuits are through the frame, with the exception of the connections between the storage battery and the starting motor.
First we will trace out the flow of current when the starting switch is closed, this circuit being shown by the heavy black lines. Current flows from the plus terminal of the storage battery out