Reciprocating Ignition Systems Battery Ignition Systemreviewed Magneto Ignition

Reciprocating Ignition Systems

Battery Ignition System--reviewed

Magneto Ignition System �AC Generator �Coil �Breaker points/condenser �Distributor

Low Tension Magneto �Flashover-Spark jumps to the wrong electrode in a high tension magneto can lead to carbon trackingfine pencil like carbon trails that short the magneto to ground. �This was first combated by the development of low tension magnetos �Later, through the use of better insulating materials and pressurized magneto housings

Low Tension Magneto components �Mechanical System �Magnetic Circuit (alternator) �Low voltage switched and distributed circuit �High voltage step-up transformer for every spark plug

Low Tension Magneto

High Tension Magneto �Better materials helped prevent flash-over within distributor �Less components needed for high voltage distribution �Most new magnetos are high tension variety �Similar to low tension except: �Single coil is used �Primary of coil is switched �Secondary of coil is distributed to all sparkplugs

High Tension Magneto

Mechanical System � Magneto Housing � Supports all of the parts � Made of Aluminum alloy( light weight, will not interfere with the magnetic circuit) � Flange mount (end mounted to accessory case) � Base Mount (bottom mounted on a shelf– require vernier coupling) � Magneto Drive Shaft � Turns the rotating magnet � Drives the distributor gear � Incorporates the cam lobe(s) � Cam � Compensated cam (one unique cam lobe per cylinder --radial engines) � Uncompensated cam (same cam lobe(s) for all cylinders)

Magnetic Circuit �Rotating Magnet �Permanent magnet � 2, 4, 8 Poles �Alnico, Permalloy �Pole shoes �Pole Shoe extensions �Core of coil

Magnetic Circuit Full register Lines of Flux Neutral register Full register

Efficiency Gap (E-Gap) - Static Flux – generated by magnet alone - Resultant Flux – combination of flux from magnet plus additional (delayed) flux generated by current passing through coil that was produced by static flux - Resultant flux is maximum a few degrees past Neutral Register - Breaker points open at E-gap angle to induce maximum magnetic field change onto secondary coil

Primary Circuit

Primary Circuit--components �Primary coil �Breaker points �Capacitor/condenser �Cam �Ignition switch/P-lead

Primary Circuit--electrical �Current is generated within coil by magnet passing in proximity to coil �Current flows out of coil through closed breaker points to ground and returns to coil �No current passes through capacitor when breaker points are closed �Magnetic pole passes neutral register and at e-gap angle, breaker points open �Capacitor momentarily takes all the current as it charges and prevents current from trying to arc across opening points—provides a “discharge” path for primary coil �Magnetic field surrounding primary coil collapses current ceases

Secondary Circuit

Secondary Circuit - components �Provides the High Voltage for the spark plug �Secondary Coil �Carbon Brush �Distributor �Spark Plug lead �Spark Plug �Some magnetos incorporate a safety gap this provides a path to ground for the high voltage in the event that a spark plug or wire becomes electrically open.

Secondary Circuit- electrical �Secondary coil consists of many loops of fine wire �As the primary coil magnetic field collapses (due to the breaker points opening) current is induced across the secondary coil �A large voltage (tens of thousands) is generated within the secondary coil �Voltage is routed through distributor rotor and contacts through a selected plug wire and spark plug �Voltage jumps gap of spark plug to return current through engine chassis to ground connection of primary coil– completes secondary circuit

Magneto Operation—putting it all together �Magneto is internally timed to induce a large magnetic flux into the secondary coil for the generation and distribution of high voltage to a spark plug �Accomplished by first developing a large magnetic field about the primary coil by passing a strong magnet past the primary �Primary magnetic field is then collapsed at maximum flux generation (e-gap) by opening the primary circuit with breaker points/condenser �Resulting primary coil magnetic field collapse induces current into secondary coil “instantaneously” producing high voltage…

Nuance stuff about magnetos �Magnetos don’t need a battery—primary advantage! �P-lead is electrically “parallel” with breaker points �P-lead “grounds” primary coil circuit �Radio Freq (RF) filter is “in line” between mag switch and breaker points �Condenser also helps prevent pitting of breaker points �Magnetos are pressurized to help prevent “tracking” in the distributor cap – pressurized air is better insulator �Magnetos are vented to prevent build up of corrosive gasses developed from arcs in distributer cap �Magnetos develop alternating “+” and “-” current

Magneto – coil (top) and rotor

Distributor gear

Distributor cap

Auxiliary Ignition systems �“Coming in” speed- speed at which magneto has to turn in order to produce a hot spark �Ignition normally occurs before piston top dead center (BTDC)– typically 30 -35 deg BTDC �When engine is starting (turning slower than “coming in” speed), this can cause hard starts and/or engine “kick back”. �To prevent this, the ignition spark must be strengthened and retarded (delayed) during starting

Auxiliary ignition units for cold starting �Impulse couplings �Induction Vibrator �Shower of sparks �Booster magnetos

Impulse coupling - Mechanism that holds the magneto magnet fixed while engine rotates and wings a magneto spring - At prescribed retarded timing, the spring is released and quickly turns the magnet generating Spark and near “coming in” speed - Thus, spark is retarded and strengthened but impulse mechanism - Impulse drops out after about 400 rpm - Can be installed on one or both magnetos - If used on one magneto, then engine is normally started on that magneto (Left)

Impluse coupling mechanism

Induction Vibrator

Induction Vibrator �Uses “bell circuit” to switch a battery current on and off across the magneto primary coil when in the “start” position �Switching battery on and off across the primary effectively creates multiple sparking cycles for each “opening” of the breaker points—instead of just one spark �When points are closed, battery switching is grounded by p 0 ints

Shower of Sparks

Shower of Sparks �Works just like Induction vibrator but action of battery switching (on and off) is controlled by a separate set of points operated off the cam

Booster Magneto

Booster Magneto � Only used on engines that have overlapping power strokes �A manually cranked magneto that throws a “shower” of sparks on the previously fired cylinder during the last of degrees of its power stroke �Directed by a lagging distributor rotor finger �