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Fig. 101.-Outlining Operation of Low Tension or Make and Break Spark Plates for Four-Cylinder
A storage battery is more suitable because it will maintain a steadier flow of current and is not exhausted so soon as primary cells, especially if the igniter plate construction is based on the use of electrical current supplied by a magneto. An igniter plate intended for use solely with batteries is devised in such a way that contact is established and broken between the points of the igniter plate only when a spark is necessary, whereas on igniter plates that operate with magneto current the points are kept permanently short-circuited or in contact together until the spark is needed in the cylinder. Where the contact points are practically always together it will be seen that the battery current would be permanently short circuited. Therefore, on most forms of low tension ignition systems the battery is supplied Fig. 102.-Low Tension Igniter Plate Used
on Locomobile Cars. only for an emergency use, as it will soon become exhausted if employed for regular ignition service.
Q. How is spark coil made, and what is the difference between low tension "kick coil” and induction coil used in high tension systems?
A. The kick coil consists of a core of soft iron wire around which is wrapped eight or ten windings of coarse magnet wire No. 16 or 18 gauge. Unlike the induction coil the "kick coil” has only one winding of coarse wire and does not employ a vibrator or condenser. It is much simpler than the induction coil, because the secondary winding, the condenser and the vibrator parts are eliminated. It is connected in series with the battery current, i. e. the positive
wire which leac's to the bus bar or to the insulated terminals of the igniter plate is connected to one of the terminals of the coil so the winding of the coil really forms an extension of the conductor leading to the igniter plates. The other battery terminal is connected to the ground through a simple form of switch.
Q. Describe construction of igniter plate.
A. A typical igniter plate which has been used successfully on many Locomobile cars is shown at Fig. 102. The view at 1 shows the exterior of the plate which is approximately triangular in form and which has three projecting lugs by which it is bolted to the combustion chamber. The interior view is shown at 2, this showing the movable hammer member, which is rocked by the simple lever extending to the tappet rod operated by the camshaft. The combination of hammer and operating lever forms a bell-crank provided with a suitable journal in the igniter plate so the hammer member can rock back and forth and establish contact with the fixed insulated member which is called the "anvil” and which is shown detached from the igniter plate at 3. The hammer is provided with a platinum contact point which normally rests against a similar contact member on the stationary anvil.
The wire conveying current from the magneto or battery is attached to the fixed terminal or anvil insulated from the main body portion of the igniter plate. The plate shown is provided with a taper joint, so that it makes a gas tight connection when inserted into the opening made to receive it in the combustion chamber wall.
The method of operation of the igniter plate is clearly outlined at Fig. 103-A. As will be seen the cam lifts the roller on the tappet rod plunger and establishes the circuit which is broken as soon as the roller rides off of the point of the cam and the contact points at the gniter plate are separated.
In the diagram at Fig. 103-B the various parts of the igniter plate operating mechanism are clearly outlined. The main current conveyer or bus bar 1 is brought into electrical connection with the insulated terminal 6 and the anvil carried in plate 3 by means of the switch lever 2. The grounded hammer member 4 is operated by the external lever 5 which establishes contact between the hammer 4 and the anvil 6 when it is raised by the rod 9 which applies its pressure through the medium of the spring 8 as the roll carrying plunger 11 is raised by the cam member in the guide bushing 10. When the roller carrier 11 drops off the point of the cam, the rod 9 is pulled down and the hammer 4 is separated from the anvil 6 by means of the nut 7 at the end of the rod 9. The spark time is advanced and retarded by sliding the igniter operating camshaft along so that the roller on the member 11 is raised sooner or later depending upon its position with reference to the inclined cam point.
Q. Is coil needed with magneto on low tension ignition system?
A. As the magneto armature may be wound with sufficient
Fig. 103.—Showing Action of Locomobile Low Tension Igniter Plate.
wire to produce a hot energetic spark a current of sufficient intensity may be produced directly from the mechanical generator without the use of a "kick-coil” such as necessary with a battery.
Q. Must magneto be timed?
A. The armature of the magneto must be timed with a certain definite relation to the crankshaft of the motor because the igniter points separate in the combustion chamber only when the magneto armature has attained that portion of a revolution where the current generation in the armature winding is at its maximum value. This means that the magneto must be driven by positive means from the engine crankshaft, and on a four cylinder engine the magneto armature runs at crankshaft speed just as in the high tension forms.
Q. What are the advantages of this system?
A. It is claimed that the low tension system of ignition is not affected by water as is the high tension form with exposed spark plugs and that it will produce a hotter spark than will the high tension system. It is widely used in marine and stationary installations but is seldom employed at the present time on motors intended as automobile power plants.