EARLY IGNITION SYSTEMS
One of the most important auxiliary groups of the gasoline engine comprising the airplane power plant and one absolutely necessary to insure engine action is the ignition system or the method employed of kindling the compressed gas in the cylinder to produce an explosion and useful power. The ignition system has been fully as well developed as other parts of the engine, and at the present time practically all ignition systems follow principles which have become standard through wide acceptance.
During the early stages of development of the gasoline engine various methods of exploding the charge of combustible gas in the cylinder were employed. On some of the earliest engines a flame burned close to the cylinder head, and at the proper time for ignition a slide or valve moved to provide an opening which permitted the flame to ignite the gas back of the piston. This system was practical only on the primitive form of gas engines in which the charge was not compressed before ignition. Later, when it was found desirable to compress the gas a certain degree before exploding it, an incandescent platinum tube in the combustion chamber, which was kept in a heated condition by a flame burning in it, exploded the gas. The naked flame was not suitable in this application because when the slide was opened to provide communication between the flame and the gas the compressed charge escaped from the cylinder with enough pressure to blow out the flame at times and thus cause irregular ignition. When the flame was housed in a platinum tube it was protected from the direct action of the gas, and as long as the tube was maintained at the proper point of incandescence regular ignition was obtained.
Some engineers utilized the property of gases firing themselves if compressed to a sufficient degree, while others depended upon the heat stored in the cylinder-head to fire the highly compressed gas. None of these methods were practical in their application to motor car engines because they did not permit flexible engine action which is so desirable. At the present time, electrical ignition systems in which the compressed gas is exploded by the heating value of the minute electric arc or spark in the cylinder are standard, and the general practice seems to be toward the use of mechanical producers of electricity rather than chemical batteries.
ELECTRICAL IGNITION BEST
Two general forms of electrical ignition systems may be used, the most popular being that in which a current of electricity under high tension is made to leap a gap or air space between the points of the sparking plug screwed into the cylinder. The other form, which has been almost entirely abandoned in automobile and which was never used with airplane engine practice, but which is still used to some extent on marine engines, is called the low-tension system because current of low voltage is used and the spark is produced by moving electrodes in the combustion chamber.
The essential elements of any electrical ignition system, either high or low tension, are: First, a simple and practical method of current production; second, suitable timing apparatus to cause the spark to occur at the right point in the cycle of engine action; third, suitable wiring and other apparatus to convey the current produced by the generator to the sparking member in the cylinder.
The various appliances necessary to secure prompt ignition of the compressed gases should be described in some detail because of the importance of the ignition system. It is patent that the scope of a work of this character does not permit one to go fully into the theory and principles of operation of all appliances which may be used in connection with gasoline motor ignition, but at the same time it is important that the elementary principles be considered to some extent in order that the reader should have a proper understanding of the very essential ignition apparatus. The first point considered will be the common methods of generating the electricity, then the appliances to utilize it and produce the required spark in the cylinder. Inasmuch as magneto ignition is universally used in connection with airplane engine ignition it will not be necessary to consider battery ignition systems.
FUNDAMENTALS OF MAGNETISM OUTLINED
To properly understand the phenomena and forces involved in the generation of electrical energy by mechanical means it is necessary to become familiar with some of the elementary principles of magnetism and its relation to electricity. The following matter can be read with profit by those who are not familiar with the subject. Most persons know that magnetism exists in certain substances, but many are not able to grasp the terms used in describing the operation of various electrical devices because of not possessing a knowledge of the basic facts upon which the action of such apparatus is based.
Magnetism is a property possessed by certain substances and is manifested by the ability to attract and repel other materials susceptible to its effects. When this phenomenon is manifested by a conductor or wire through which a current of electricity is flowing it is termed “electro-magnetism.” Magnetism and electricity are closely related, each being capable of producing the other. Practically all of the phenomena manifested by materials which possess magnetic qualities naturally can be easily reproduced by passing a current of electricity through a body which, when not under electrical influence, is not a magnetic substance. Only certain substances show magnetic properties, these being iron, nickel, cobalt and their alloys.
The earliest known substance possessing magnetic properties was a stone first found in Asia Minor. It was called the lodestone or leading stone, because of its tendency, if arranged so it could be moved freely, of pointing one particular portion toward the north. The compass of the ancient Chinese mariners was a piece of this material, now known to be iron ore, suspended by a light thread or floated on a cork in some liquid so one end would point toward the north magnetic pole of the earth. The reason that this stone was magnetic was hard to define for a time, until it was learned that the earth was one huge magnet and that the iron ore, being particularly susceptible, absorbed and retained some of this magnetism.
Most of us are familiar with some of the properties of the magnet because of the extensive sale and use of small horseshoe magnets as toys. As they only cost a few pennies every one has owned one at some time or other and has experimented with various materials to see if they would be attracted. Small pieces of iron or steel were quickly attracted to the magnet and adhered to the pole pieces when brought within the zone of magnetic influence. It was soon learned that brass, copper, tin or zinc were not affected by the magnet. A simple experiment that serves to illustrate magnetic attraction of several substances is shown at A, Fig. 57. In this, several balls are hung from a standard or support, one of these being of iron, another of steel. When a magnet is brought near either of these they will be attracted toward it, while the others will remain indifferent to the magnetic force. Experimenters soon learned that of the common metals only iron or steel were magnetic.
Fig. 57.—Some Simple Experiments to Demonstrate Various Magnetic Phenomena and Clearly Outline Effects of Magnetism and Various Forms of Magnets.
Magnets are commonly made in two forms, either in the shape of a bar or horseshoe. These two forms are made in two types, simple or compound. The latter are composed of a number of magnets of the same form united so the ends of like polarity are laced together, and such a construction will be more efficient and have more strength than a simple magnet of the same weight. The two common forms of simple and compound magnets are shown at C, Fig. 57. The zone in which a magnetic influence occurs is called the magnetic field, and this force can be graphically shown by means of imaginary lines, which are termed “lines of force.” As will be seen from the diagram at D, Fig. 57, the lines show the direction of action of the magnetic force and also show its strength, as they are closer together and more numerous when the intensity of the magnetic field is at its maximum. A simple method of demonstrating the presence of the force is to lay a piece of thin paper over the pole pieces of either a bar or horseshoe magnet and sprinkle fine iron filings on it. The particles of metal arrange themselves in very much the manner shown in the illustrations and prove that the magnetic field actually exists.
The form of magnet used will materially affect the size and area of the magnetic field. It will be noted that the field will be concentrated to a greater extent with the horseshoe form because of the proximity of the poles. It should be understood that these lines have no actual existence, but are imaginary and assumed to exist only to show the way the magnetic field is distributed. The magnetic influence is always greater at the poles than at the center, and that is why a horseshoe or U-form magnet is used in practically all magnetos or dynamos. This greater attraction at the poles can be clearly demonstrated by sprinkling iron filings on bar and U magnets, as outlined at E, Fig. 57. A large mass gathers at the pole pieces, gradually tapering down toward the point where the attraction is least.
From the diagrams it will be seen that the flow of magnetism is from one pole to the other by means of curved paths between them. This circuit is completed by the magnetism flowing from one pole to the other through the magnet, and as this flow is continued as long as the body remains magnetic it constitutes a magnetic circuit. If this flow were temporarily interrupted by means of a conductor of electricity moving through the field there would be a current of electricity induced in the conductor every time it cut the lines of force. There are three kinds of magnetic circuits. A non-magnetic circuit is one in which the magnetic influence completes its circuit through some substance not susceptible to the force. A closed magnetic circuit is one in which the influence completes its circuit through some magnetic material which bridges the gap between the poles. A compound circuit is that in which the magnetic influence passes through magnetic substances and non-magnetic substances in order to complete its circuit.
HOW IRON AND STEEL BARS ARE MADE MAGNETIC
Magnetism may be produced in two ways, by contact or induction. If a piece of steel is rubbed on a magnet it will be found a magnet when removed, having a north and south pole and all of the properties found in the energizing magnet. This is magnetizing by contact. A piece of steel will retain the magnetism imparted to it for a considerable length of time, and the influence that remains is known as residual magnetism. This property may be increased by alloying the steel with tungsten and hardening it before it is magnetized. Any material that will retain its magnetic influence after removal from the source of magnetism is known as a permanent magnet. If a piece of iron or steel is brought into the magnetic field of a powerful magnet it becomes a magnet without actual contact with the energizer. This is magnetizing by magnetic induction. If a powerful electric current flows through an insulated conductor wound around a piece of iron or steel it will make a magnet of it. This is magnetizing by electro-magnetic induction. A magnet made in this manner is termed an electro-magnet and usually the metal is of such a nature that it will not retain its magnetism when the current ceases to flow around it. Steel is used in all cases where permanent magnets are required, while soft iron is employed in all cases where an intermittent magnetic action is desired. Magneto field magnets are always made of tungsten steel alloy, so treated that it will retain its magnetism for lengthy periods.
ELECTRICITY AND MAGNETISM CLOSELY RELATED
There are many points in which magnetism and electricity are alike. For instance, air is a medium that offers considerable resistance to the passage of both magnetic influence and electric energy, although it offers more resistance to the passage of the latter. Minerals like iron or steel are very easily influenced by magnetism and easily penetrated by it. When one of these is present in the magnetic circuit the magnetism will flow through the metal. Any metal is a good conductor for the passage of the electric current, but few metals are good conductors of magnetic energy. A body of the proper metal will become a magnet due to induction if placed in the magnetic field, having a south pole where the lines of force enter it and a north pole where they pass out.
We have seen that a magnet is constantly surrounded by a magnetic field and that an electrical conductor when carrying a current is also surrounded by a field of magnetic influence. Now if the conductor carrying a current of electricity will induce magnetism in a bar of iron or steel, by a reversal of this process, a magnetized iron or steel bar will produce a current of electricity in a conductor. It is upon this principle that the modern dynamo or magneto is constructed. If an electro-motive force is induced in a conductor by moving it across a field of magnetic influence, or by passing a magnetic field near a conductor, electricity is said to be generated by magneto-electric induction. All mechanical generators of the electric current using permanent steel magnets to produce a field of magnetic influence are of this type.
BASIC PRINCIPLES OF MAGNETO OUTLINED
The accompanying diagram, Fig. 58, will show these principles very clearly. As stated on an earlier page, if the lines of force in the magnetic field are cut by a suitable conductor an electrical impulse will be produced in that conductor. In this simple machine the lines of force exist between the poles of a horseshoe magnet. The conductor, which in this case is a loop of copper wire, is mounted upon a spindle in order that it may be rotated in the magnetic field to cut the lines of magnetic influence present between the pole pieces. Both of the ends of this loop are connected, one with the insulated drum shown upon the shaft, the other to the shaft. Two metal brushes are employed to collect the current and cause it to flow through the external circuit. It can be seen that when the shaft is turned in the direction of the arrow the loop will cut through the lines of magnetic influence and a current will be generated therein.
Fig. 58
Fig. 58.—Elementary Form of Magneto Showing Principal Parts Simplified to Make Method of Current Generation Clear.
The pressure of the current and the amount produced vary in accordance to the rapidity with which the lines of magnetic influence are cut. The armature of a practical magneto, therefore, differs materially from that shown in the diagram. A large number of loops of wire would be mounted upon this shaft in order that the lines of magnetic influence would be cut a greater number of times in a given period and a core of iron used as a backing for the wire. This would give a more rapid alternating current and a higher electro-motive force than would be the case with a smaller number of loops of wire.
Fig. 59
Fig. 59.—Showing How Strength of Magnetic Influence and of the Currents Induced in the Windings of Armature Vary with the Rapidity of Changes of Flow.
The illustrations at Fig. 59 show a conventional double winding armature and field magnetic of a practical magneto in part section and will serve to more fully emphasize the points previously made. If the armature or spindle were removed from between the pole pieces there would exist a field of magnetic influence as shown at Fig. 57, but the introduction of this component provides a conductor (the iron core) for the magnetic energy, regardless of its position, though the facility with which the influence will be transmitted depends entirely upon the position of the core. As shown at A, the magnetic flow is through the main body in a straight line, while at B, which position the armature has attained after one-eighth revolution, or 45 degrees travel in the direction of the arrow, the magnetism must pass through in the manner indicated. At C, which position is attained every half revolution, the magnetic energy abandons the longer path through the body of the core for the shorter passage offered by the side pieces, and the field thrown out by the cross bar disappears. On further rotation of the armature, as at D, the body of the core again becomes energized as the magnetic influence resumes its flow through it. These changes in the strength of the magnetic field when distorted by the armature core, as well as the intensity of the energy existing in the field, affect the windings, and the electrical energy induced therein corresponds in strength to the rapidity with which these changes in magnetic flow occur. The most pronounced changes in the strength of the field will occur as the armature passes from position B to D, because the magnetic field existing around the core will be destroyed and again re-established.
During the most of the armature rotation the changes in strength will be slight and the currents induced in the wire correspondingly small; but at the instant the core becomes remagnetized, as the armature leaves position C, the current produced will be at its maximum, and it is necessary to so time the rotation of the armature that at this instant one of the cylinders is in condition to be fired. It is imperative that the armature be driven in such relation to the crank-shaft that each production of maximum current coincides with the ignition point, this condition existing twice during each revolution of the armature, or at every 180 degrees travel. Each position shown corresponds to 45 degrees travel of the armature, or one-eighth of a turn, and it takes just three-eighths revolution to change the position from A to that shown at D.
ESSENTIAL PARTS OF A MAGNETO AND THEIR FUNCTIONS
The magnets which produce the influence that in turn induces the electrical energy in the winding or loops of wire on the armature, and which may have any even number of opposed poles, are called field magnets. The loops of wire which are mounted upon a suitable drum and rotate in the field of magnetic influence in order to cut the lines of force is called an armature winding, while the core is the metal portion. The entire assembly is called the armature. The exposed ends of the magnets are called pole pieces and the arrangement used to collect the current is either a commutator or a collector. The stationary pieces which bear against the collector or commutator and act as terminals for the outside circuit are called brushes. These brushes are often of copper, or some of its alloys, because copper has a greater electrical conductivity than any other metal.
These brushes are nearly always of carbon, which is sometimes electroplated with copper to increase its electrical conductivity, though cylinders of copper wire gauze impregnated with graphite are utilized at times. Carbon is used because it is not so liable to cut the metal of the commutator as might be the case if the contact was of the metal to metal type. The reason for this is that carbon has the peculiar property in that it materially assists in the lubrication of the commutator, and being of soft, unctuous composition, will wear and conform to any irregularities on the surface of the metal collector rings.
The magneto in common use consists of a number of horseshoe magnets which are compound in form and attached to suitable cast-iron pole pieces used to collect and concentrate the magnetic influence of the various magnets. Between these pole pieces an armature rotates. This is usually shaped like a shuttle, around which are wound coils of insulated wire. These are composed of a large number of turns and the current produced depends in great measure upon the size of the wire and the number of turns per coil. An armature winding of large wire will deliver a current of great amperage, but of small voltage. An armature wound with very fine wire will deliver a current of high voltage but of low amperage. In the ordinary form of magneto, such as used for ignition, the current is alternating in character and the break in the circuit should be timed to occur when the armature is at the point of its greatest potential or pressure. Where such a generator is designed for direct current production the ends of the winding are attached to the segments of a commutator, but where the instrument is designed to deliver an alternating current one end of the winding is fastened to an insulator ring on one end of the armature shaft and the other end is grounded on the frame of the machine.
The quantity of the current depends upon the strength of the magnetic field and the number of lines of magnetic influence acting through the armature. The electro-motive force varies as to the length of the armature winding and the number of revolutions at which the armature is rotated.
THE TRANSFORMER SYSTEM USES LOW VOLTAGE MAGNETO
The magneto in the various systems which employ a transformer coil is very similar to a low-tension generator in general construction, and the current delivered at the terminals seldom exceeds 100 volts. As it requires many times that potential or pressure to leap the gap which exists between the points of the conventional spark plug, a separate coil is placed in circuit to intensify the current to one of greater capacity. The essential parts of such a system and their relation to each other are shown in diagrammatic form at Fig. 60 and as a complete system at Fig. 61. As is true of other systems the magnetic influence is produced by permanent steel magnets clamped to the cast-iron pole pieces between which the armature rotates. At the point of greatest potential in the armature winding the current is broken by the contact breaker, which is actuated by a cam, and a current of higher value is induced in the secondary winding of the transformer coil when the low voltage current is passed through the primary winding.
Fig. 60
Fig. 60.—Diagrams Explaining Action of Low Tension Transformer Coil and True High Tension Magneto Ignition Systems.
Large
image
(95 kB).
Fig. 60A
Fig. 60A.—Side Sectional View of Bosch High-Tension Magneto Shows Disposition of Parts. End Elevation Depicts Arrangement of Interruptor and Distributor Mechanism.
It will be noted that the points of the contact breaker are together except for the brief instant when separated by the action of the point of the cam upon the lever. It is obvious that the armature winding is short-circuited upon itself except when the contact points are separated. While the armature winding is thus short-circuited there will be practically no generation of current. When the points are separated there is a sudden flow of current through the primary winding of the transformer coil, inducing a secondary current in the other winding, which can be varied in strength by certain considerations in the preliminary design of the apparatus. This current of higher potential or voltage is conducted directly to the plug if the device is fitted to a single-cylinder engine, or to the distributor arm if fitted to a multiple-cylinder motor. The distributor consists of an insulator in which is placed a number of segments, one for each cylinder to be fired, and so spaced that the number of degrees between them correspond to the ignition points of the motor. A two-cylinder motor would have two segments, a three-cylinder, three segments, and so on within the capacity of the instrument. In the illustration a four-cylinder distributor is fitted, and the distributing arm is in contact with the segment corresponding to the cylinder about to be fired.
Fig. 61
Fig. 61.—Berling Two-Spark Dual Ignition System.
TRUE HIGH-TENSION MAGNETOS ARE SELF-CONTAINED
The true high-tension magneto differs from the preceding inasmuch as the current of high voltage is produced in the armature winding direct, without the use of the separate coil. Instead of but one coil, the armature carries two, one of comparatively coarse wire, the other of many turns of finer wire. The arrangement of these windings can be readily ascertained by reference to the diagram B, Fig. 60, which shows the principle of operation very clearly. The simplicity of the ignition system is evident by inspection of Fig. 62. One end of the primary winding (coarse wire) is coupled or grounded to the armature core, and the other passes to the insulated part of the interrupter. While in some forms the interrupter or contact breaker mechanism does not revolve, the desired motion being imparted to the contact lever to separate the points of a revolving cam, in this the cam or tripping mechanism is stationary and the contact breaker revolves. This arrangement makes it possible to conduct the current from the revolving primary coil to the interrupter by a direct connection, eliminating the use of brushes, which would otherwise be necessary. In other forms of this appliance where the winding is stationary, the interrupter may be operated by a revolving cam, though, if desired, the used of a brush at this point will permit this construction with a revolving winding.
Fig. 62
Fig. 62.—Berling Double-Spark Independent System.
During the revolution of the armature the grounded lever makes and breaks contact with the insulated point, short-circuiting the primary winding upon itself until the armature reaches the proper position of maximum intensity of current production, at which time the circuit is broken, as in the former instance. One end of the secondary winding (fine wire) is grounded on the live end of the primary, the other end being attached to the revolving arm of the distributor mechanism. So long as a closed circuit is maintained feeble currents will pass through the primary winding, and so long as the contact points are together this condition will exist. When the current reaches its maximum value, because of the armature being in the best position, the cam operates the interrupter and the points are separated, breaking the short circuit which has existed in the primary winding.
The secondary circuit has been open while the distributor arm has moved from one contact to another and there has been no flow of energy through this winding. While the electrical pressure will rise in this, even if the distributor arm contacted with one of the segments, there would be no spark at the plug until the contact points separated, because the current in the secondary winding would not be of sufficient strength. When the interrupter operates, however, the maximum primary current will be diverted from its short circuit and can flow to the ground only through the secondary winding and spark-plug circuit. The high pressure now existing in the secondary winding will be greatly increased by the sudden flow of primary current, and energy of high enough potential to successfully bridge the gap at the plug is thereby produced in the winding.
THE BERLING MAGNETO
The Berling magneto is a true high tension type delivering two impulses per revolution, but it is made in a variety of forms, both single and double spark. Its principle of action does not differ in essentials from the high tension type previously described. This magneto is used on Curtiss aviation engines and will deliver sparks in a positive manner sufficient to insure ignition of engines up to 200 horse-power and at rotative speeds of the magneto armature up to 4,000 r. p. m. which is sufficient to take care of an eight-cylinder V engine running up to 2,000 r. p. m. The magneto is driven at crank-shaft speed on four-cylinder engines, at 11/2 times crank-shaft speed on six-cylinder engines and at twice crank-shaft speed on eight-cylinder V types. The types “D” and “DD” BERLING Magnetos are interchangeable with corresponding magnetos of other standard makes. The dimensions of the four-, six- and eight-cylinder types “D” and “DD” are all the same.
Fig. 63
Fig. 63.—Type DD Berling High Tension Magneto.
The ideal method of driving the magneto is by means of flexible direct connecting coupling to a shaft intended for the purpose of driving the magneto. As the magneto must be driven at a high speed, a coupling of some flexibility is preferable. The employment of such a coupling will facilitate the mounting of the magneto, because a small inaccuracy in the lining up of the magneto with the driving shaft will be taken care of by the flexible coupling, whereas with a perfectly rigid coupling the line-up of the magneto must be absolutely accurate. Another advantage of the flexible coupling is that the vibration of the motor will not be as fully transmitted to the armature shaft on the magneto as in case a rigid coupling is used. This means prolonged life for the magneto.
The next best method of driving the magneto is by means of a gear keyed to the armature shaft. When this method of driving is employed, great care must be exercised in providing sufficient clearance between the gear on the magneto and the driving gear. If there should be a tight spot between these two gears it will react disadvantageously on the magneto. The third available method is to drive the magneto by means of a chain. This is the least desirable of the three methods and should be resorted to only in case of absolute necessity. It is difficult to provide sufficient clearance when using a chain without rendering the timing less accurate and positive.
Fig. 64
Fig. 64.—Wiring Diagrams of Berling Magneto Ignition Systems.
Fig. 64, A shows diagrammatically the circuit of the “D” type two-spark independent magneto and the switch used with it. In position OFF the primary winding of the magneto is short-circuited and in this position the switch serves as an ordinary cut-out or grounding switch. In position “1” the switch connects the magneto in such a way that it operates as an ordinary single-spark magneto. In this position one end of the secondary winding is grounded to the body of the motor. This is the starting position. In this position of the switch the entire voltage generated in the magneto is concentrated at one spark-plug instead of being divided in half. With the motor turning over very slowly, as is the case in starting, the full voltage generated by the magneto will not in all cases be sufficient to bridge simultaneously two spark gaps, but is amply sufficient to bridge one. Also, this position of the switch tends to retard the ignition and should be used in starting to prevent back-firing. With the switch in position “2” the magneto applies ignition to both plugs in each cylinder simultaneously. This is the normal running position.
Fig. 64, B shows diagrammatically the circuit of the type “DD” BERLING high-tension two-spark dual magneto. This type is recommended for certain types of heavy-duty airplane motors, which it is impossible to turn over fast enough to give the magneto sufficient speed to generate even a single spark of volume great enough to ignite the gas in the cylinder. The dual feature consists of the addition to the magneto of a battery interrupter. The equipment consists of the magneto, coil and special high-tension switch. The coil is intended to operate on six volts. Either a storage battery or dry cells may be used.
With the switch in the OFF position, the magneto is grounded, and the battery circuit is open. With the switch in the second or battery position marked “BAT,” one end of the secondary winding of the magneto is grounded, and the magneto operates as a single-spark magneto delivering high-tension current to the inside distributor, and the battery circuit being closed the high-tension current from the coil is delivered to the outside distributor. In this position the battery current is supplied to one set of spark plugs, no matter how slowly the motor is turned over, but as soon as the motor starts, the magneto supplies current as a single-spark magneto to the other set of the spark-plugs. After the engine is running, the switch should be thrown to the position marked “MAG.” The battery and coil are then disconnected, and the magneto furnishes ignition to both plugs in each cylinder. This is the normal running position. Either a non-vibrating coil type “N-1” is furnished or a combined vibrating and non-vibrating coil type “VN-1.”
SETTING BERLING MAGNETO
The magneto may be set according to one of two different methods, the selection of which is, to some extent, governed by the characteristics of the engine, but largely due to the personal preference on the part of the user. In the first method described below, the most advantageous position of the piston for fully advanced ignition is determined in relation to the extreme advanced position of the magneto. In this case, the fully retarded ignition will not be a matter of selection, but the timing range of the magneto is wide enough to bring the fully retarded ignition after top-center position of the piston. The second method for the setting of the magneto fixes the fully retarded position of the magneto in relation to that position of the piston where fully retarded ignition is desired. In this case, the extreme advance position of the magneto will not always correspond with the best position of the piston for fully advanced ignition, and the amount of advance the magneto should have to meet ideal requirements in this respect must be determined by experiment.
First Method:
1. Designate one cylinder as cylinder No. 1.
2. Turn the crank-shaft until the piston in cylinder No. 1 is in the position where the fully advanced spark is desired to occur.
3. Remove the cover from the distributor block and turn the armature shaft in the direction of rotation of the magneto until the distributor finger-brush comes into such a position that this brush makes contact with the segment which is connected to the cable terminal marked “1.” This is either one of the two bottom segments, depending upon the direction of rotation.
4. Place the cam housing in extreme advance, i.e., turn the cam housing until it stops, in the direction opposite to the direction of rotation of the armature. With the cam housing in this position, open the cover.
5. With the armature in the approximate position as described in “3,” turn the armature slightly in either direction to such a point that the platinum points of the magneto interrupter will just begin to open at the end of the cam, adjacent to the fibre lever on the interrupter.
6. With this exact position of the armature, fix the magneto to the driving member of the engine.
Second Method:
1. Designate one cylinder as cylinder No. 1.
2. Turn the crank-shaft until the piston in cylinder No. 1 is in the position at which the fully retarded spark is desired to occur.
3. Same as No. 3 under First Method.
4. Place the cam housing in extreme retard, i.e., turn the cam housing until it stops, in the same direction as the direction of rotation of the armature. With the cam housing in this position, open the cover.
5. Same as No. 5 under First Method.
6. Same as No. 6 under First Method.
WIRING THE MAGNETO
The wiring of the magneto is clearly shown by wiring diagram.
First determine the sequence of firing for the cylinders and then connect the cables to the spark plug in the cylinders in proper sequence, beginning with cylinder No. 1 marked on the distributor block.
The switch used with the independent type must be mounted in such a manner that there will be a metallic connection between the frame of the magneto and the metal portion of the switch.
It is advisable to use a separate battery, either storage or dry cells, as a source of current for the dual equipment. Connecting to the same battery that is used with the generator and other electrical equipment may cause trouble, as a “ground” in this battery causes the coil to overheat.
CARE AND MAINTENANCE
Lubrication:
Use only the very best of oil for the oil cups.
Put five drops of oil in the oil cup at the driving end of the magneto for every fifty hours of actual running.
Put five drops of oil in the oil cup at the interrupter end of the magneto, located at one side of the cam housing, for every hundred hours of actual running.
Lubricate the embossed cams in the cam housing with a thin film of vaseline every fifty hours of actual running. Wipe off all superfluous vaseline. Never use oil in the interrupter. Do not lubricate any other part of the interrupter.
Adjusting the Interrupter:
With the fibre lever in the center of one of the embossed cams, as at Fig. 65, the opening between the platinum contacts should be not less than .016'' and not more than .020''. The gauge riveted to the adjusting wrench should barely be able to pass between the contacts when fully open. The platinum contacts must be smoothed off with a very fine file. When in closed position, the platinum contacts should make contact with each other over their entire surfaces.
Fig. 65
Fig. 65.—The Berling Magneto Breaker Box Showing Contact Points Separated and Interruptor Lever on Cam.
When inspecting the interrupter, make sure that the ground brush in the back of the interrupter base is making good contact with the surface on which it rubs.
Cleaning the Distributor:
The distributor block cover should be removed for inspection every twenty-five hours of actual running and the carbon deposit from the distributor finger-brush wiped off the distributor block by rubbing with a rag or piece of waste dipped in gasoline or kerosene. The high-tension terminal brush on the side of the magneto should also be carefully inspected for proper tension.
LOCATING TROUBLE
Trouble in the ignition system is indicated by the motor “missing,” stopping entirely, or by inability to start.
It is safe to assume that the trouble is not in the magneto, and the carburetor, gasoline supply and spark-plugs should first be investigated.
If the magneto is suspected, the first thing to do is to determine if it will deliver a spark. To determine this, disconnect one of the high-tension leads from the spark-plug in one of the cylinders and place it so that there is approximately 1/16'' between the terminal and the cylinder frame.
Open the pet cocks on the other cylinders to prevent the engine from firing and turn over the engine until the piston is approaching the end of the compression stroke in the cylinder from which the cable has been removed. Set the magneto in the advance position and rapidly rock the engine over the top-center position, observing closely if a spark occurs between the end of the high-tension cable and the frame.
If the magneto is of the dual type, the trouble may be either in the magneto or in the battery or coil system, therefore disconnect the battery and place the switch in the position marked “MAG.” The magneto will then operate as an independent magneto and should spark in the proper manner. After this the battery system should be investigated. To test the operation of the battery and coil, examine all connections, making sure that they are clean and tight, and then with the switch, in the “BAT,” rock the piston slowly back and forth. If a type “VN-1” coil is used, a shower of sparks should jump between the high-tension cable terminal and the cylinder frame when the piston is in the correct position for firing. If no spark occurs, remove the cover from the coil and see that the vibrating tongue is free. If a type “N-1” coil is used, a single spark will occur. The battery should furnish six volts when connected to the coil, and this should also be verified.
If the coil still refuses to give a spark and all connections are correct, the coil should be replaced and the defective coil returned to the manufacturer.
If both magneto and coil give a spark when tested as just described, the spark-plugs should be investigated. To do this, disconnect the cables and remove the spark-plugs. Then reconnect the cables to the plugs and place them so that the frame portions of the plugs are in metallic connection with the frame of the motor. Then turn over the motor, thus revolving the magneto armature, and see if a spark is produced at the spark gaps of the plugs.
The most common defects in spark-plugs are breaking down of the insulation, fouling due to carbon, or too large or small a spark gap. To clean the plugs a stiff brush and gasoline should be used. The spark gap should be about 1/32'' and never less than 1/64''. Too small a gap may have been caused by beads of metal forming due to the heat of the spark. Too long a gap may have been caused by the points burning off.
If the magneto and spark plugs are in good condition and the engine does not run satisfactorily, the setting should be verified according to instructions previously given, and, if necessary, readjusted.
Be careful to observe that both the type “VN-1” and type “N-1” coils are so arranged that the spark occurs on the opening of the contacts of the timer. As this is just the reverse of the usual operation, it should be carefully noted when any change in the setting of the timer is made. The timer on the dual type magneto is adjusted so that the battery spark occurs about 5° later than the magneto spark. This provides an automatic advance as soon as the switch is thrown to the magneto position “MAG.” This relative timing can be easily adjusted by removing the interrupter and shifting the cam in the direction desired.
Fig. 66
Fig. 66.—The Dixie Model 60 for Six-Cylinder Airplane Engine Ignition.
THE DIXIE MAGNETO
The Dixie magneto, shown at Fig. 66, operates on a different principle than the rotary armature type. It is used on the Hall-Scott and other aviation engines. In this magneto the rotating member consists of two pieces of magnetic material separated by a non-magnetic center piece. This member constitutes true rotating poles for the magnet and rotates in a field structure, composed of two laminated field pieces, riveted between two non-magnetic rings. The bearings for the rotating poles are mounted in steel plates, which lie against the poles of the magnets. When the magnet poles rotate, the magnetic lines of force from each magnet pole are carried directly to the field pieces and through the windings, without reversal through the mass of the rotating member and with only a single air gap. There are no losses by flux reversal in the rotating part, such as take place in other machines, and this is said to account for the high efficiency of the instrument.
Fig. 67
Fig. 67.—Installation Dimensions of Dixie Model 60 Magneto.
Fig. 68
Fig. 68.—The Rotating Elements of the Dixie Magneto.
And this “Mason Principle” involved in the operation of the Dixie is simplified by a glance at the field structure, consisting of the non-magnetic rings, assembled to which are the field pieces between which the rotating poles revolve (see Fig. 68). Rotating between the limbs of the magnets, these two pieces of magnetic material form true extensions to the poles of the magnets, and are, in consequence, always of the same polarity. It will be seen there is no reversal of the magnetism through them, and consequently no eddy current or hysteresis losses which are present in the usual rotor or inductor types. The simplicity features of construction stand out prominently here, in that there are no revolving windings, a detail entirely differing from the orthodox high-tension instrument. This simplicity becomes instantly apparent when it is found that the circuit breaker, instead of revolving as it does in other types, is stationary and that the whole breaker mechanism is exposed by simply turning the cover spring aside and removing cover. This makes inspection and adjustment particularly simple, and the fact that no special tool is necessary for adjustment of the platinum points—an ordinary small screw-driver is the whole “kit of tools” needed in the work of disassembling or assembling—is a feature of some value.
Fig. 69
Fig. 69.—Suggestions for Adjusting and Dismantling Dixie Magneto. A—Screw Driver Adjusts Contact Points. B—Distributor Block Removed. C—Taking off Magnets. D—Showing How Easily Condenser and High Tension Windings are Removed.
With dust- and water-protecting casing removed, and one of the magnets withdrawn, as in Fig. 69, the winding can be seen with its core resting on the field pole pieces and the primary lead attached to its side. An important feature of the high-tension winding is that the heads are of insulating material, and there is not the tendency for the high-tension current to jump to the side as in the ordinary armature type magneto. The high-tension current is carried to the distributor by means of an insulated block with a spindle, at one end of which is a spring brush bearing directly on the winding, thus shortening the path of the high-tension current and eliminating the use of rubber spools and insulating parts. The moving parts of the magneto need never be disturbed if the high-tension winding is to be removed. This winding constitutes all of the magneto windings, no external spark coil being necessary. The condenser is placed directly above the winding and is easily removable by taking out two screws, instead of being placed in an armature where it is inaccessible except to an expert, and where it cannot be replaced except at the factory whence it emanated.
CARE OF THE DIXIE MAGNETO
The bearings of the magneto are provided with oil cups and a few drops of light oil every 1,000 miles are sufficient. The breaker lever should be lubricated every 1,000 miles with a drop of light oil, applied with a tooth-pick. The proper distance between the platinum points when separated should not exceed .020 or one-fiftieth of an inch. A gauge of the proper size is attached to the screwdriver furnished with the magneto. The platinum contacts should be kept clean and properly adjusted. Should the contacts become pitted, a fine file should be used to smooth them in order to permit them to come into perfect contact. The distributor block should be removed occasionally and inspected for an accumulation of carbon dust. The inside of the distributor block should be cleaned with a cloth moistened with gasoline and then wiped dry with a clean cloth. When replacing the block, care must be exercised in pushing the carbon brush into the socket. Do not pull out the carbon brushes in the distributor because you think there is not enough tension on the small brass springs. In order to obtain the most efficient results, the normal setting of the spark-plug points should not exceed .025 of an inch, and it is advisable to have the gap just right before a spark-plug is inserted.
The spark-plug electrodes may be easily set by means of the gauge attached to the screwdriver. The setting of the spark-plug points is an important function which is usually overlooked, with the result that the magneto is blamed when it is not at fault.
TIMING OF THE DIXIE MAGNETO
In order to obtain the utmost efficiency from the engine, the magneto must be correctly timed to it. This operation is usually performed when the magneto is fitted to the engine at the factory. The correct setting may vary according to individuality of the engine, and some engines may require an earlier setting in order to obtain the best results. However, should the occasion arise to retime the magneto, the procedure is as follows: Rotate the crank-shaft of the engine until one of the pistons, preferably that of cylinder No. 1, is 1/16 of an inch ahead of the end of the compression stroke. With the timing lever in full retard position, the driving shaft of the magneto should be rotated in the direction in which it will be driven. The circuit breaker should be closely observed and when the platinum contact points are about to separate, the drive gear or coupling should be secured to the drive shaft of the magneto. Care should be taken not to alter the position of the magneto shaft when tightening the nut to secure the gear or coupling, after which the magneto should be secured to its base. Remove the distributor block and determine which terminal of the block is in contact with the carbon brush of the distributor finger and connect with plug wire leading to No. 1 cylinder to this terminal. Connect the remaining plug wires in turn according to the proper sequence of firing of the cylinders. (See the wiring diagram for a typical six-cylinder engine at Fig. 70.) A terminal on the end of the cover spring of the magneto is provided for the purpose of connecting the wire leading to a ground switch for stopping the engine.
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Fig. 69A Fig. 69A.—Sectional Views Outlining Construction of Dixie Magneto with Compound Distributor for Eight-Cylinder Engine Ignition.
