C H A P T E R 10 Ignition Systems

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Describe the primary purpose of the ignition system. Identify the components in a typical magneto system and describe the function of each part. Identify the three general classifications of magneto ignition systems and explain the operation of each. Describe the operation of a battery ignition system. Learning Objectives

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Ignition Systems Provide voltage to discharge spark –Jumps spark plug gap –Ignites compressed air-fuel mixture –30,000 volts Magneto systems –No outside primary source of electricity

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Magneto System Components –Magnets –Spark plug –Spark plug wire –Ignition coil –Switching device

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Magneto System

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Ignition Coil Operates like transformer Two separate windings –Primary windings have relatively few turns –Secondary windings have many turns –High voltage produced in secondary windings –Secondary voltage causes spark

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Spark Plug Inserted into combustion chamber Ignites compressed air-fuel mixture Many variations Ribs on insulator prevent flashover Center electrode carries high voltage to the spark plug gap Spark plug reach varies from one type of plug to another

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Spark Plug (Deere & Co.)

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Spark Plug Heat Transfer Spark plugs manufactured in various heat ranges –Cold plugs transfer heat readily –Length of insulator nose determines how well heat travels –Insulator nose tip hottest part of plug Can cause preignition or plug fouling

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Spark Plug Wire Connects ignition coil output to spark plug Heavily insulated –Deteriorated insulation leads to arcing Spark plug connections –Exposed clip –Boot type

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Switching Devices Control primary current to coil –Mechanical or electronic Mechanical breaker points –Tungsten contacts Electronic switching devices –No moving parts to burn or wear out

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Magneto Ignition System Classified by type of switching device –Capacitor discharge ignition –Transistor-controlled ignition –Mechanical breaker point ignition Mechanical or solid state –Solid state used in all late-model engines

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Magneto Ignition Systems Compared

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Advantage of Solid State Ignition Adjustments not required Increased plug live Easy starting Uniform performance Improved idling and smoother operation under load

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Capacitive Discharge Ignition (CDI) Stores primary energy in capacitor Uses semiconductors for triggering system and timing Compact and maintenance free –Flywheel magnets only moving parts

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Capacitive Discharge Ignition

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Transistor-Controlled Ignition System Inductive system Transistors used for triggering Many variations –Unique characteristics

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Transistor-Controlled Ignition Components

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Transistor-Controlled Ignition Circuit

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Mechanical Breaker Point Ignition System Components –Coil –Condenser Prevents arcing –Breaker points Mechanically actuated –Flywheel Magnets Alnico

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Mechanical Breaker Point Ignition System

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Dwell (Cam Angle) Time breaker points stay closed during one revolution of cam Measured in degrees of cam rotation from point closing to point opening Inverse relationship between point gap and dwell –Large point produces short dwell –Small point opening produces larger dwell Changing point setting can change spark timing

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Ignition Advance Systems Some engines with MBI systems have mechanical ignition advance systems –Retard occurrence of spark for timing –Cause spark to occur earlier in cycle for intermediate and high-speed operation

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Magneto Ignition System for Two-Cylinder Engines Two coil assemblies located 180 degrees apart –As flywheel passes one of the coils, corresponding spark plug fires Waste spark system –Single coil assembly with two secondary outputs –Both plugs fire at same time –One piston on compression stroke and other on exhaust stroke

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Battery Ignition System Major Components –Coil –Switching device –Spark plug –Battery Lead-acid battery is the source of primary current

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Battery Ignition System Components (Kohler Co.) Replace with Figure from SGE ©2017 Replace Image with Figure from SGE (2017), page 202

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Battery Ignition System Operation (Kohler Co.) Replace with Figure from SGE ©2017 Replace Image with Figure from SGE (2017), page 202

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Battery Ignition System Operation (Kohler Co.) Replace with Figure from SGE ©2017 Replace Image with Figure from SGE (2017), page 203

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Ignition Coil Serves as step-up transformer Increases low primary voltage into high voltage Primary winding consists of approximately 200 turns of heavy wire Secondary winding has 20,000 turns of fine wire

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Lead-Acid Battery Sole source of energy in battery ignition system –Wet-charged batteries supplied with electrolyte in them –Dry-charged batteries must have electrolyte installed after purchase Generator replenishes energy in battery

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Battery Construction Hard rubber case Six cells –Cells contain specific number of positive and negative plates –Positive plates have lead oxide covering –Negative plates have porous surface The more plates per cell, the higher the ampere- hour rating of the battery

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Battery Construction

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Battery Discharging/Charging Cycle Discharging –Chemical reaction between plates and electrolyte –Battery attempts to equalize potential difference between plates Charging –Direct current passes through battery in reverse direction –Current causes a reversal in chemical reaction and restores plates and electrolyte