Зображення сторінки
PDF
ePub
[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small]

Fig. 176.-Wiring Diagram of Delco-Buick Starting, Lighting and Ignition System.

of water in the tank increases the pressure in the pipe line also becomes greater, and this increased pressure acting through the pressure cylinder flows into the valve and thereby decreases the flow of water. When the tank is about full of water the valve is so nearly closed that only a small amount of water is pumped. Considering the action from an electrical point of view, when the storage battery is discharged it offers but little resistance to the flow of the charging current. It does not require much voltage to produce a current flow in a circuit of low resistance so the current regulating plunger will remain low in its tube, this allowing a large quantity of current to be generated. As the storage battery becomes charged the pressure on the line increases and this acting through the voltage regulating coil lifts the plunger out of the mercury and reduces the flow of current. When the storage battery is fully charged the regulating plunger is nearly all out of the mercury and only a small amount of electricity is .supplied to the battery.

It will be noticed that in the wiring diagram shown at Fig. 176 a protective circuit breaker is attached to the switchboard. The function of this device is to open the circuit between the source of current supply (generator and storage battery) and the current consuming units (lamps, horn and ignition apparatus) if one of the wires leading to a current consuming unit happens to become grounded. Under such a condition an excessive flow of current is possible on account of the lessened resistance of the circuit. Such a flow goes through the winding of the circuit breaking relay or protected circuit breaker, which produces a magnetic pull that opens the contact and cuts off the current supply. As soon as the contact is opened the magnetic pull ceases and the contact is closed again, re-establishing the magnetic pull and again opening the contact. The circuit breaker will continue to vibrate until the ground or short circuit is located and corrected whenever any one of the switches controlling the current consuming units is pushed in to establish a circuit. The function of this protective circuit breaker is the same as a fuse block and fuse except that it is not necessary to keep replacing fuses.

Method of Current Output Regulation.—The voltage regulator which has been previously described and which was used on the 1914 Delco Systems has been replaced by a system of "third brush excitation” in the 1916 systems. This has been very concisely described by the Delco engineers, and in order to make for accurate presentation of fact, the following descriptive matter is given in the same way as it appears in the Delco instruction books.

There is really only one point in regard to the generating of electrical energy which is difficult to understand, and the best of scientists are at as much of a loss on this point as the average electrician. This one point can be expressed in the one sentence which is as follows: "Whenever the strength of the magnetic field or the amount of magnetism within a coil is changed an electro-motive force is induced or generated.” This is variously expressed, but can be resolved into the same sentence as originally given. One of the most common expressions is, “Whenever an electrical conductor cuts the magnetic field or cuts magnetic lines of force an electromotive force is induced.” In order to measure this electro-motive force, it is necessary to make connection from each end of the conductor to a suitable meter, by doing this a coil would be formed. Therefore, this expression means nothing different from the original expression. On account of being more readily understood, this expression will be referred to in connection with the explanation of the action of the generator.

The amount of the voltage that is induced (or generated) in any conductor or coil varies directly with the rate of the cutting of the magnetic lines; e.g., if we have a generator in which the magnetic field remains constant and the generator produces 7 volts at 400 R. P. M., the voltage at 800 R. P. M. would be 14 volts, and it is on account of the variable speed of generators for automobile purposes that they must be equipped with some means of regulation for holding the voltage very nearly constant. The regulation of this generator is by what is known as third brush excitation, the theory of which is as follows:

The motor generator consists essentially of an iron frame and a field coil with two windings for magnetizing this frame. The armature, which is the revolving element, has wound in slots on its iron

core a motor winding and a generator winding connected to corresponding commutators. Each commutator has a corresponding set of brushes which are for the purpose of collecting current from, or delivering current to the armature windings while the armature is revolving.

When cranking, current from the storage battery flows through the motor winding magnetizing the armature core. This acting upon the magnetism of the frame causes the turning effort. When generating the voltage is induced in the generator winding and when the circuit is completed to the storage battery this causes the charging current to flow into the battery. The brushes are located on the commutator in such a position that they collect the current while it is being generated in one direction. (The current flows one direction in a given coil while it is passing under one pole piece and in the other direction when passing under the opposite pole piece.) When the ignition button on the combination switch is first pulled out the current flows from the storage battery through the generator armature winding, also through the shunt field winding. This causes the motoring of the generator. After the engine is started and is running on its own power this current still has a tendency to flow in this direction, but is opposed by the voltage generated. At very low speeds a slight discharge is obtained. At approximately 7 miles per hour the generated voltage exceeds that of the battery and charging commences. As the speed increases above this point the charging rate increases as shown by the curve (Fig. 174). The regulation of this generator is affected by what is known as third brush excitation.

Since the magnetic field of the generator is produced by the current in the shunt field winding it is evident that should the shunt field current decrease as the speed of the engine increases the regulation would be affected. In order to fully understand this explanation it must be borne in mind that a current of electricity always has a magnetic effect whether this is desirable or not. Referring to Fig. 177, the theory of this regulation is as follows: The full voltage of the generator is obtained from the large brushes marked “C” and “D.” When the magnetic field from the pole pieces N and S is not disturbed by any other influence each coil is

[ocr errors]

UU

generating uniformly as it passes under the pole pieces. The voltage from one commutator bar to the next one is practically uni

form around the commutator. Therefore,

the voltage from brush 00000000000

C to brush E is about 5 volts when the total voltage from brush C to brush D is 61/2 volts and 5 volts is applied to the shunt field winding. This 5 volts is sufficient to cause approximately 1/4 amperes to flow in the

shunt field winding. Fig. 177.—Diagram Showing Delco Third

As the speed of the Brush Excitation Regulating Principles. generator is increased

the voltage increases, causing the current to be charged to the storage battery. This charging current flows through the armature winding, producing a magnetic effect in the direction of the arrow B. This magnetic effect acts upon the main magnetic field which is in the direction of the arrow A, with the result that the magnetic field is twisted out of its original position in very much the same manner as two streams of water coming together are each deflected from their original directions. This deflection causes the magnetic field to be strong at the pole tips, marked G and F, and weak at the opposite pole tips with the result that the coils generate a very low voltage while passing from the brush C to the brush E (the coils at this time are under the pole tips having a weak field) and generates a greater part of their voltage while passing from the brush E to D. The amount of this variation depends upon the speed that the generator is driven; with the result that the shunt field current decreases as the speed increases as shown in the curve.

By this form of regulation it is possible to get a high charging rate between the speeds of 12 and 25 miles per hour, and it is with

« НазадПродовжити »