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the cable causes the finger to engage with one of the shoulders, and thus turn the flywheel.
Q. How do electric starters work and how are they classified ?
A. Electric lighting, cranking and ignition systems for motor cars are of such recent development that it is not possible to describe all systems used for this purpose. Not only do the individual systems vary in detail, but the components of the same system are often of different construction when used on cars of different makes. The standard equipment must include three important functions, namely, the generator which is driven by the engine end which produces electric current to keep a storage battery charged, and the starting motor which is in mechanical connection with the engine and in electrical connection with the storage battery when it is desired to turn the engine over for starting. If the motor and generator are combined in one instrument the starting system is known as a one unit type. If the motor is one appliance and the generator another, the system is said to be a two unit system. Each of these has advantages, and both forms have demonstrated that they are thoroughly practical.
Q. Name other parts of electric starting system.
A. In addition to the three main items enumerated, various accessories, such as switches, ammeters, connectors, wiring, protective circuit breakers, automatic current regulators, etc., are necessary for the convenient distribution and control of the electric current.
Q. Describe arrangement of parts of “one unit” system.
A. The elements of a one unit system are shown in diagram form at the bottom of Fig. 353. It will be observed that the armature carries two commutators, one of which is used when the armature is driven by the engine, and when the device serves as a current generator, the other being employed when the operating conditions are reversed and the electrical machine is acting as a motor to turn over the engine crankshaft. When the device is driven as a generator the small sliding pinion on the short end
Fig. 353.—Diagrams Showing Relation of Parts of Typical Electrical Start
ing Systems. That at Top is a Three Unit while that Depicted Below is a One Unit Form.
of the shaft is out of engagement with the spur gear cut on the flywheel exterior. When it is desired to start the engine the spur gear is meshed with the member cut on the flywheel and the current from the storage battery is directed to the windings of the electric machine which becomes a motor and which turns over the engine crankshaft. When the device is working as a generator the current that is developed goes to the storage battery, and from that member to the various current consuming units.
Sometimes the motor and generator are combined in one casing and the system so provided is erroneously called a "one unit” system. In reality such a system is a two unit systen, because the electrical machines are uni-functional instead of performing a dual function as does the combined-motor-generator at the right of the illustration. The wiring of the one unit system is shown in simplified form and should be easily followed by any motorist.
Q. Outline arrangement of parts of “two unit” system.
A. The parts of a two unit starting and lighting system are shown at Fig. 353. This system is sometimes called a "three unit” system, on account of having a source of independent current supply for ignition purposes. This is shown as fitted to the Overland six-cylinder engine at Fig. 354. As will be observed, the generator in the diagram is driven from the motor crankshaft by silent chain connections, one of the terminals passing through the cut-out device and to the storage battery, the other terminal running directly to the storage battery terminal having a short by-pass or shunt wire attached to the cut-out. All the time that the engine is running the generator is delivering electricity to the storage battery.
It will be seen that the storage battery is also coupled to the lighting circuits which are shown in a group at the right of the illustration, and to the electric starting motor as indicated. One of the storage battery terminals is joined directly to the switch terminal by a suitable conductor, the other goes to one of the terminals on the starting motor, while the remaining terminal of the starting motor goes to the switch. In this system, when the small sliding pinion is meshed with the flywheel gear, the switch
Fig. 354.-Illustration Showing Location of Starting, Lighting and Igni
tion Units on the Overland Six Cylinder Engine.
is thrown on simultaneously, and the current that flows from the storage battery through the windings of the starting motor rotates the engine crankshaft by means of reduction gears shown. As soon as the engine starts the foot is released and a spring pulls the switch out of contact, and also disengages the sliding pinion from the flywheel gear.
Fig. 355.–Moline-Knight Power Plant Showing Application of Starting Motor with Automatic Pinion Shift and Method of Driving Generator.
Q. What is the difference between a "three unit" and the others described? .
A. In referring to a system as a one unit system of lighting, starting and ignition, one means that all of these functions are incorporated in one device, as in the Delco system. If one unit is used for generating the lighting and starting current, and also is reversible to act as a motor, but a separate ignition means is provided such as a high tension magneto, thc system is called a