Automotive Electrical & Electronic Systems Classroom Manual

Page 267

ker88839_ch11.qxd

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11:31 AM

Page 255

The Ignition: Primary and Secondary Circuits and Components

SUMMARY Through electromagnetic induction, the ignition system transforms the low voltage of the battery into the high voltage required to fire the spark plugs. Induction occurs in the ignition coil where current travels through the primary winding to build up a magnetic field. When the field rapidly collapses, high voltage is induced in the coil secondary winding. All domestic original-equipment ignitions are the battery-powered, inductivedischarge type. The ignition system is divided into two circuits: primary and secondary. The primary circuit contains the battery, the ignition switch, the coil primary winding, a switching device, and signal devices to determine crankshaft position. For over sixty years, mechanical breaker points were used as the primary circuit-switching device. Solid-state electronic components replaced breaker points as the switching device in the 1970s. The two most common solid-state switching devices are the magnetic pulse generator and the Hall Effect switch. The breaker points are a mechanical switch that opens and closes the primary circuit. The time period when the points are closed is called the dwell angle. The dwell angle varies inversely with the gap between the points when they are open. As the gap decreases, the dwell increases. The ignition condenser is a capacitor that absorbs primary voltage when the points open. This prevents arcing across the points and premature burning. Three types of common ignition electronic signal devices are the magnetic pulse generator, the Hall Effect switch, and the optical signal generator. The magnetic pulse generator creates an ac voltage signal as the reluctor continually passes the pole piece, changing the induced voltage to negative. The Hall Effect switch uses a stationary

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sensor and rotating trigger wheel just like the magnetic pulse generator. Its main advantage over the magnetic pulse generator is that it can generate a full-strength output voltage signal even at slow speeds. The optical signal generator acts both as the crankshaft position CKP sensor and TDC sensor, as well as a switching device. It uses light beam interruption to generate voltage signals. The ignition secondary circuit generates the high voltage and distributes it to the engine to ignite the combustion charge. This circuit contains the coil secondary winding, the distributor cap and rotor, the ignition cables, and the spark plugs. The ignition coil produces the high voltage necessary to ionize the spark plug gap through electromagnetic induction. Low-voltage current in the primary winding induces high voltage in the secondary winding. A coil must be installed with the same primary polarity as the battery to maintain proper secondary polarity as the battery to maintain proper secondary polarity at the spark plugs. Available voltage is the amount of voltage the coil is capable of producing. Required voltage is the voltage necessary to ionize and fire the spark plugs under any given operating condition. Voltage reserve is the difference between available voltage and required voltage. A welltuned ignition system should have a 60-percent voltage reserve. The spark plugs allow the high voltage to arc across an air gap and ignite the air-fuel mixture in the combustion chamber. Important design features of a spark plug are its reach, heat range, thread and seat size, and the air gap. Other special features of spark plugs are the use of resistors, extended tips, wide gaps, and copper cores. For efficient spark plug firing, ignition polarity must be established so that the center electrode of the plug is negative and the ground electrode is positive.


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Articles inside

Summary

4min
page 363

Cruise Control Systems

3min
pages 357-358

Review Questions

3min
pages 364-366

Radios and Entertainment Systems

6min
pages 337-339

Theft Deterrent Systems

7min
pages 353-356

Heated Seats

6min
pages 343-345

Power Seats

2min
pages 341-342

Power Door Locks, Trunk Latches, and Seat- Back Releases

2min
page 346

Heating and Air-Conditioning Systems

12min
pages 328-334

Class 2 IPM-Controlled HVAC Systems

2min
pages 335-336

Review Questions

1min
page 326

Summary

1min
page 325

Windshield Wipers and Washers

10min
pages 319-324

Summary

1min
page 314

Review Questions

2min
pages 315-316

Head-Up Display (HUD

5min
pages 311-313

Electromagnetic Instrument Circuits

11min
pages 296-300

Review Questions

2min
pages 293-294

Malfunction Indicator Lamp (MIL

5min
pages 301-303

Summary

1min
page 292

Instrument Panel and Interior Lamp Circuits

4min
pages 289-291

Circuits

1min
page 288

Backup Lamp Circuits Side Marker and Clearance Lamp

1min
page 287

Circuits

2min
page 286

Stop Lamp and Turn Signal Circuits Hazard Warning Lamp (Emergency Flasher)

6min
pages 282-285

Taillamp, License Plate Lamp, and Parking Lamp Circuits

1min
page 281

Common Automotive Bulbs

1min
page 280

Headlamp Circuits

16min
pages 270-279

Summary

1min
page 267

Review Questions

1min
page 268

Spark Plug Construction

4min
pages 264-266

Distributor Cap and Rotor

3min
pages 259-261

Primary and Secondary Circuits

1min
page 248

Voltages

4min
pages 246-247

Basic Circuits and Current

1min
page 241

Silicon-Controlled Rectifiers (SCRs

1min
page 233

Review Questions

2min
pages 236-238

Summary

1min
page 235

Transistors

9min
pages 229-232

Rectifier Circuits

2min
page 228

Semiconductors

7min
pages 222-224

Photonic Semiconductors

2min
page 227

Review Questions

3min
pages 218-220

Starter Motor and Drive Types

8min
pages 210-214

DC Starter Motor Operation

5min
pages 206-208

Summary

2min
pages 216-217

Overrunning Clutch

1min
page 215

Specific Starting Systems

6min
pages 200-203

Summary

2min
pages 191-192

Differences

13min
pages 183-190

Review Questions

3min
pages 193-194

Charge/Voltage/Current Indicators

3min
pages 180-181

Solid-state Regulators

9min
pages 175-179

Electromagnetic Regulators

1min
page 174

Voltage Regulation

2min
page 173

Current Production in an AC Generator

9min
pages 168-172

Diode Rectification

3min
pages 162-163

AC Generator (Alternator) Components

7min
pages 164-167

Review Questions

4min
pages 157-158

Battery Installations

4min
pages 150-151

Battery Installation Components

2min
pages 152-153

Summary

2min
page 156

Battery Life and Performance Factors

5min
pages 154-155

State-of-Charge Indicators Wet-Charged and Dry-Charged

2min
page 147

Battery Electrolyte

2min
page 146

Electrochemical Action

8min
pages 142-145

Review Questions

3min
pages 138-140

Wire Color Coding

2min
pages 121-122

Multiplex Circuits

8min
pages 112-114

Ground Paths

2min
page 111

Connectors and Terminals

5min
pages 108-110

Wire Size

6min
pages 105-107

Wire Types and Materials

2min
page 104

Wiring and Harnesses

2min
pages 102-103

Review Questions

4min
pages 97-100

Parallel Circuit Voltage Drops Calculating Series Circuit Total

1min
page 87

Series and Parallel Circuit Faults

3min
pages 94-95

Series-Parallel Circuits

4min
pages 91-93

Review Questions

2min
page 82

Summary

3min
pages 80-81

Electromagnetism

9min
pages 67-71

Electromagnetic Induction

11min
pages 72-76

Magnetism

2min
page 66

Power

2min
page 56

Capacitance

8min
pages 57-60

Review Questions

2min
pages 62-64

Summary

1min
page 61

Complete Electrical Circuit

3min
pages 52-53

Summary

2min
page 43

Historical Figures in Electricity

2min
page 42

Fire Extinguishers

1min
page 31

Safety Tips for Technicians

2min
pages 25-26

Nuts

1min
page 15

Review Questions

2min
pages 44-46

Electrical Cord Safety

1min
pages 29-30

Safety in Lifting (Hoisting) a Vehicle

2min
pages 27-28
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