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generator by means of armature reaction, a reversed series field winding or weakening the magnetic field in some way when the engine speed is excessive. The governors usually permit a maximum generator output of from ten to twelve amperes, though the normal charging current is less than this figure.
Q. How is a generator wound for "inherent” regulation?
A. The Westinghouse generators for example, with inherent regulation have a compound field winding. The battery charging current passes through the series winding in such direction that any increase in the battery charging current tends to reduce the voltage generated, so that the battery is never charged at an excessive rate. When the lights are burning, however, current flows through this series winding in the reverse direction, increasing the output of the generator and causing it to assist the battery in carrying the load. With the usual lamp equipment, this increase in generator output is sufficient to operate the lamps without any demand on the battery at ordinary running speeds. At low speeds the battery supplies a certain proportion of the lighting current, and when the engine is not running, the battery supplies the entire demand.
Q. How do generators with automatic potential regulators work?
A. The generators with automatic potential regulators maintain constant voltage regardless of whether the battery is connected to the system or not. The characteristics are such that the battery-charging current tapers off as the battery charge increases, being very large when the battery is in a discharged condition and of low value when the battery is fully charged. The voltage is independent of the speed and the amount of lighting load. The regulator consists of a vibrating armature that intermittently short-circuits a high resistance in series with the shunt field winding of the generator, the length of the short-circuit period depending on the load on the generator.
Fig. 359.-Front View of King Eight Cylinder Power Plant Showing
Silent Chain Drive to Generator.
Q. How does the motorist know that an electrical system is working correctly?
A. In practically all systems an amperemeter is mounted on the dash so that it can be readily inspected by the driver, this
indicating at all times the amount of current being produced by the dynamo or drawn from the battery. If the indicating needle of the amperemeter points to the left of the zero point on the scale, it means that the battery is furnishing current to the lights or other current consuming units or discharging. When the needle points to the other side of the scale, it means that the generator is delivering current to the battery which is charging it, the amount of charge or discharge at any time can be read from the scale on the face of the amperemeter. Some of these instruments have the words "charge" and "discharge" under the scale in order to enable the operator to read the instrument correctly.
Q. What types of switches are used and how do they differ?
A. Another important element is the lighting switch, which is usually mounted at some point within convenient reach of the car driver. This is often placed on an instrument board on the back of the cowl in connection with other registering instruments. As ordinarily constructed, the switches are made up of a number of units, and the wiring is such that the head, side and tail lamps may be controlled independently of each other. For simplicity and convenience of installation, the switch is usually arranged so that all circuits are wired to parallel connecting members or "busbars” placed at the rear of the switch. In some cars, as the latest Overland and the White models, the switch units are placed on the steering column. As but little current passes through the lighting switch the contacts are not heavy in construction as are those of the starting switch.
The function of the starting switch is to permit the current to flow from the storage battery to the starting motor, when it is necessary to start the car. It is arranged usually so as to be readily operated by the foot and is nearly always installed at some convenient position on the toe board of the car. As we have previously shown, the starting switch is often interlocked with the starting motor gearing so that the operation of engaging the gear with the flywheel and of turning on the current to the starting motor are accomplished simultaneously. The lighting and motor starting wiring systems are independent of each other, and may be easily found as that used to convey the high amperage starting current is of heavy round single conductor cable, while the lighting wiring is usually a light multiple strand cable. In order to prevent chafing and depreciation of the insulation the wiring is often protected by conduits of a flexible metal tubing, and the terminals are extremely heavy and well adapted to resist the vibration which is unavoidable in automobiles.
Q. How are current generators driven?
A. When electric lighting was first applied to automobiles it was not considered necessary to drive the generators by positive connection, and the early devices were furnished with pulleys for flat or V belt drive. At the present time it is considered highly important to provide a positive mechanical connection that will not slip between the generator and the engine crankshaft. The common systems where the generator is a separate unit from the starting motor and in those forms where the starting and generating functions are combine], involve a connection with the motor crankshaft through some form of gearing. As shown in Fig. 355, the generator is driven by means of a leather universal joint connection with an extension of the pump shaft. The motor crankshaft imparts its power through the camshaft timing gear to the small pinion utilized in driving the water pump. In some generator applications a belt is used, and at Fig. 359 the armature is rotated by silent chain connection with a gear on the motor crankshaft. There is not the diversity of drives for the generator as there is in the methods of connecting the starting motor to the end of the crankshaft.
Q. What are the advantages of silent chain drive?
A. In describing the advantages of silent chain drive the Dyneto Company writes as follows: “The exact type of drive selected must, of course, depend upon conditions. If possible, use a silent chain drive, direct to the crankshaft, with a suitable casing so that the chain can run in oil with all dirt excluded. In our opinion this will give the most quiet, durable and efficient drive obtainable. We recommend, when space allows, the use of chains of 12" pitch x 12" width. When sprockets of small diameter must be used, chains of 38" pitch x 1" width will be satisfactory. Sprockets of less than 15 teeth should never be used; 17 teeth would be much better. The efficiency of a good chain drive, well installed, is from 94 to 96%. If a gear drive is used, the gears must be of the best material and large enough to stand up under the enormous strains of starting. It is usually impossible to design a suitable gear drive of single reduction, and where three of four gears are used the drive is apt to be noisy, and certainly will be very inefficient. In tests of drives, using four gears in the train, spiral cut teeth, we have found an efficiency of less than 65%. A useless waste of 35% makes it necessary to use a larger starter, a larger battery, larger wires, and in fact the whole outfit must be much larger than otherwise would be necessary.
Q. How is the starting motor connected to the engine crankshaft to rotate it for starting?
A. In order to show the variety of driving means used in connecting the starting motor to do the work of turning over the engine crankshaft, the leading systems have been grouped in one illustration at the top of Fig. 360. Starting from the front of the motor, the first method shown is by means of a worm gear initial or primary reduction and chain connection from the wormdriven shaft to the motor crankshaft. In some cars the worm reduction is used having the starting motor mounted at the side of the change speed gear box instead of attached to the motor crankshaft. The reduction in speed may be by means of the spur gears and chain, as shown at A-2, or by a chain to a shaft connected with the timing gear, as in A-3. The method at A-4 is a very popular one, including a reduction to an intermediate shaft, which carries a sliding pinion designed to engage the gear on the flywheel rim. The method at A-5 is used with the Rushmore starter, the pinion being brought into direct engagement with the gear on the flywheel by the axial movement of the armature when the current is supplied to the field winding. The method