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4 de novembro de 2016 | 2
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Outline
• Ignition system: definition, functionality, requirements
• Ignition timing
• Spark generation
• Ignition systems evolution
• Electromechanical ignition systems
• distributor, circuit breaker, condenser, resistor, vacuum/centrifugal advance, primary/secondary voltage, dwell, distributor cap, cabling, coils
• ECU-based and distributorless ignition systems
• Capacitive and inductive discharge igniters
• Glossary
• Recommended references
4 de novembro de 2016 | 3
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Ignition System: definition
• Definition of ignition system
• system that enables to ignite the air-fuel mixture in spark-ignition
(SI) internal combustion engines (e.g. gasoline, LPG, alcohol)
http://www.engihub.com/ignition-systems-of-i-c-engine/
4 de novembro de 2016 | 4
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Ignition system: functionality
• Functionalities of an ignition system
• detection of crankshaft position/speed
• mechanical switch (circuit breaker) electronic sensor
• determination of ignition timing/duration
• mechanical computer-controlled
• creation of high-voltage
• electric transformer (known as ignition coil)
• timely distribution of high-voltage to each cylinder
• mechanical distributor power electronics
• creation of an electric arc (triggering air-fuel ignition)
• spark plug(s)
…
4 de novembro de 2016 | 5
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Ignition system: requirements
• Main requirements of an ignition system
• spark must be vigorous (so that all air/fuel mixture is burned)
• requires high-voltage peak (> 15 kV)
• spark/ignition timing must be optimized for all engine conditions
• e.g. RPM, engine load, air/fuel ratio, water temperature,…
• energy-efficient, lightweight, compact, low-cost
• low electrical energy consumption, low heat losses, high-tech materials and design; these properties may be conflicting
• durable and reliable
• user expectations: the lifetime of the vehicle; these properties and the former may be conflicting
• minimized generation of electromagnetic interference (EMI)
• EMI impacts electronic/computerized and wired/wireless communication systems
…
4 de novembro de 2016 | 6
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Ignition timing: the need for firing the spark before TDC
• Ignition must be triggered before the piston reaches TDC
• air-fuel mixture takes a few miliseconds to ignite – ignition delay
• spark must be fired a few ms before piston reaches TDC
http://suprasport.com/E3-Spark-Plugs_p_1520.html
4 de novembro de 2016 | 7
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Ignition timing: the need to adapt to engine speed
• Ignition must be triggered in advance to TDC
• this advance timing (t) is reflected in an advance angle ()
• Considering the valve timing diagram in the figure:
• intake valve opens
@ 10° BTDC
• air-fuel mixture is sucked
till intake valve closes
• air-fuel mix is compressed
till spark occurs
@ 12º BTDC
http://4mechtech.blogspot.pt/2014/12/port-timing-diagram-for-two-stroke-petrol-engine.html
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Ignition timing: the need to adapt to engine speed
• For higher RPM (), same t corresponds to > angle
( = .t)
• thus, the advance angle must be increased with the RPM
http://mechsapiens.com/valve-timing-diagram-mechanical-factor-dynamic-factor-intake-exhaust/
http://www.c5ignitions.com/c5-technology.html
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Ignition timing: the need to adapt to engine load
• Engine load
• “is the power that the outside world takes away from the engine”
• an engine connected to nothing can have essentially no load, regardless of throttle opening or RPM
• an engine produces more power and can therefore accommodate more load when its throttle is open wider, and less power/load when its throttle is less open
• the amount of power available from the engine at 100% throttle varies over its operating RPM range; at any given speed, the maximum power that the engine can output is "full load."
• if the output power of the engine is less than the external load, the engine will decelerate.
• if the output power of the engine is greater than the external load, the engine will accelerate.
http://mechsapiens.com/valve-timing-diagram-mechanical-factor-dynamic-factor-intake-exhaust/
http://www.c5ignitions.com/c5-technology.html
4 de novembro de 2016 | 10
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Ignition timing: the need to adapt to engine load
• The leaner the air/fuel mixture, the longer it takes to burn
• < engine loads > advance angle
• richer mixtures (higher loads) < advance angle
http://www.stealth316.com/2-ignitionsystem.htm
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Ignition timing: the need to adapt to engine load
• Another example with a 3D map representation
http://www.teglerizer.com/fi/bem/Basics%20of%20engine%20management.htm
4 de novembro de 2016 | 12
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Ignition timing: influence of other parameters
• Ignition timing may be optimized according to other engine
operating parameters, e.g.
• engine coolant temperature
• intake air density, temperature, pressure, mass flow rate
• throttle position
• exhaust gas oxygen
• transmission gear
• vehicle speed
• system voltage
• engine knocking
• Nowadays, this is possible due to ECU-controlled ignition
• but it was not quite like that at the beginning
http://www.stealth316.com/2-ignitionsystem.htm
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Basic principle of spark generation
https://www.thinglink.com/scene/616979999844466690
• A spark is an electric arc generated by a spark plug • when a high-voltage (tens of kV) is applied to its terminals
• This is achieved by an electric transformer (know as ignition coil) • primary winding few turns
• secondary winding many turns
• Operation 1. an electric current circulates in the primary winding
2. this current is switched off (mechanical or electronic switch)
3. there is a sudden drop in the magnetic field generated by the primary winding (a high counter-EMF appears in the primary)
4. this abrupt drop in the magnetic field induces a very high EMF in the secondary winding
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Basic principle of spark generation
https://www.picoauto.com/library/automotive-guided-tests/secondary-vs-primary-voltage-and-current1
• Example primary current and voltage waveforms Primary
ON
Primary
OFF
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Basic principle of spark generation
https://www.picoauto.com/library/automotive-guided-tests/primary-vs-secondary
• Example primary and secondary voltage waveforms
• …
4 de novembro de 2016 | 16
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Basic principle of spark generation
https://www.thinglink.com/scene/616979999844466690
• The spark generation is still the basic principle has been
applied over the years
• sparks are still used
• ignition coils are still used
• But ignition-related technology has evolved tremendously
• spark plugs
• ignition coils
• primary circuit breaker/switching
• engine parameters determination
• ignition timing optimization
• high-voltage distribution
4 de novembro de 2016 | 17
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Ignition System: evolution over time
https://www.eeweb.com/blog/fairchild_semiconductor/introduction-to-automotive-ignition-systems
Igniter
4 de novembro de 2016 | 18
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Ignition System: evolution over time
https://www.eeweb.com/blog/fairchild_semiconductor/introduction-to-automotive-ignition-systems
• From a power electronics-oriented perspective
• IGBT’s control IC with diagnosis/protection functions into igniter
4 de novembro de 2016 | 19
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Ignition coil types
http://www.ngkntk.co.uk/index.php/technical-centre/ignition-coils-tec/ignition-coils-types/
• Different types/generations of ignition coils
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Distributor types
http://www.auto-repair-help.com/automotive_maintenance/distributor_overview.php
• Different types/generations of distributors
http://www.silvesterv8.co.nz/pages.php?pageid=13 http://www.vintagemodelairplane.com/pages/Downloads/Rover_Tasters/Ignition04.html
http://www.aliexpress.com/w/wholesale-ignition-distributor.html
Coil on cap Igniter No advance 1st generation
4 de novembro de 2016 | 21
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Electromechanical ignition
• Distributor does timing advance and high-voltage distribution
• Mechanical switch
(circuit breaker)
• Centrifugal advance
• Vacuum advance
• Mechanical distributor
(distributor cap)
• High-voltage
wiring
• cylindrical coil
• Voltage divider
(primary resistor)
• Protecting condenser
… http://www.carparts.com/classroom/ignition.htm
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http://www.motorera.com/dictionary/di.htm
http://www.howacarworks.com/illustrations/inside-a-bosch-distributor
Electromechanical ignition: distributor
4 de novembro de 2016 | 23
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Electromechanical ignition: circuit breaker
• Circuit breaker (AKA breaker points)
• electrical switch, actuated by distributor cam lobes
• platinum contacts, resilient to electric arc created by CEMF
… http://modelabasics.com/Ignition.htm
4 de novembro de 2016 | 24
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Electromechanical ignition: primary current/voltage
• When primary current (few A) is cut off, a peak of counter
EMF (hundreds of V) shows up at the breaker terminals
• this creates an electric arc between the breaker points, accelerating
their deterioration
http://www.pikit.co.uk/peugeotmt/scope%20primary%20wave.html
Primary current & voltage waveforms
4 de novembro de 2016 | 25
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Electromechanical ignition: dwell
• Dwell (angle) is the number of degrees the distributor cam
rotates from the time the points close until they open again
• it affects the magnetic buildup of the primary windings: the longer
the points are closed, the greater the magnetic buildup
• too much dwell can result in point arcing and burning
• too small, the points will open and collapse the field before it has
built up enough voltage to produce a satisfactory spark
• it can be mechanically adjusted
• this concept also applies to
electronic ignitions
http://autonewpro.blogspot.pt/p/all-about-ignition-system.html
4 de novembro de 2016 | 26
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Electromechanical ignition: dwell
• Spark burn and dwell periods (secondary voltage waveform)
http://www.crypton.co.za/Tto%20know/Ignition/burn%20time.html
4 de novembro de 2016 | 27
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Electromechanical ignition: condenser
• Electric arc between the circuit breaker terminals causes slower current drop • so the magnetic field drop will not be as sharp as it should
• leading to
• smaller voltage spike
• weaker spark
• A condenser is connected in parallel with the circuit breaker • avoids electric arc between breaker points
• enables abrupt drop of current/magnetic field drop
• higher secondary voltage spike
• stronger spark
• condenser charges during the dwell period
• when the breaker opens, the condenser discharges itself through the primary coil in the opposite direction to the flow of induced current, reversing the polarity of the coil and increasing the rate at which the magnetic field collapses
http://www.uq.edu.au/_School_Science_Lessons/UNPh32.5.html#32.5.5.2
http://www.pikit.co.uk/peugeotmt/scope%20primary%20wave.html
4 de novembro de 2016 | 28
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Electromechanical ignition: condenser
• The condenser can be mounted inside or outside the
distributor
• typical capacity ≈ 0,2 F
http://www.howacarworks.com/ignition-system/fitting-a-condenser
4 de novembro de 2016 | 29
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Electromechanical ignition: primary/ballast resistor
• There is a system voltage drop during cranking
• due starter motor peak load (hundreds of A)
• typically around 3-4 V (12 8-9 V)
• This would mean either
• dimensioning the ignition coil for cranking (9 V)
overvoltage at runtime
• dimensioning the ignition coil for runtime (14 V)
undervoltage at engine cranking
• Thus
• the ignition coil is dimensioned for 9 V
• after cranking, a voltage divider
(ballast resistor) is used (1-2 Ω)
http://cny.mgcarclub.com/electrical_systems.htm
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Electromechanical ignition: centrifugal advance
• As RPM increases, upper part of the distributor shaft twists in
relation to the lower part of the distributor shaft
• centrifugal force of the inertial masses vs springs force
• (it usually works together with the vacuum advance mechanism)
… http://www.carparts.com/classroom/ignition.htm
Low RPM High RPM
4 de novembro de 2016 | 31
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Electromechanical ignition: centrifugal advance
• Example advance angle versus RPM curve
• note that the distributor speed is half the crankshaft speed
… http://www.sparkingplugs.com/8.html
4 de novembro de 2016 | 32
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Electromechanical ignition: vacuum advance
• A diaphragm reacts to engine load (intake air pressure)
• < load leaner mix > vacuum > advance (> time to burn)
• > load richer mix < vacuum < advance (< time to burn)
… http://www.carparts.com/classroom/ignition.htm
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Electromechanical ignition: vacuum advance
• Example advance angle vs. intake vacuum curve
• advance angle grows with vacuum
• adjustable mechanism
… http://www.crankshaftcoalition.com/wiki/Hot_rodding_the_HEI_distributor
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Electromechanical ignition: centrifugal advance
• Combination of centrifugal and vacuum advance
• these mechanisms work together for controlling the timing advance
… http://www.carparts.com/classroom/ignition.htm
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Electromechanical ignition: mechanical distributor (cap)
• High-voltage is transmitted from center terminal, to rotor
head, to side terminals (head rotates with distributor shaft)
• precise synchronization between high-voltage peak and rotor position
http://www.counterpersontraining.com/index.cfm?go=lms.module&moduleid=71&mode=train&contentIndex=12&topicId=269
http://newautoaa.blogspot.pt/p/secondary-circuit-of-ignition-system.html
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Electromechanical ignition: high-voltage cabling
• Requirements
• high dielectric insulation
• high EMI suppression
• high temperature resistance (> 200ºC)
• high mechanical robustness
• robustness to salt water, oil, petrol and acids
• High electrical resistance feature
• ignition cables feature high electrical resistance (several kΩ)
• this minimizes EMI radiation; since electrical current is
minimized, the radiated electromagnetic field is also minimized
• this does not affect the spark plug voltage peak
• ignition cables conduct a high-voltage low-energy signal
https://www.ngk.de/en/technology-in-detail/ignition-cables/principles/
http://www.my-cardictionary.com/zuendung/zuendleitungen-zuendkabel.html
4 de novembro de 2016 | 37
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Electromechanical ignition: high-voltage cabling
• There are three different types of ignition cables
• copper cables (EMI suppression resistor in the connectors/plug)
• carbon cables (carbon resistance in the cable)
• ignition cables with inductive resistor
• They mainly differ based on
• the material used for the conductor
• the type of resistor used for interference suppression
https://www.ngk.de/en/technology-in-detail/ignition-cables/principles/
http://www.my-cardictionary.com/zuendung/zuendleitungen-zuendkabel.html
4 de novembro de 2016 | 38
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Electromechanical ignition: high-voltage cabling
• Copper ignition cables
• copper core surrounded by a silicone casing (electrical insulator)
• the interference suppression resistor is integrated in the spark plug
connector, in the coil connector or in the spark plug (1-6 kΩ)
https://www.ngk.de/en/technology-in-detail/ignition-cables/principles/
http://www.ngk-sparkplugs.jp/english/techinfo/qa/q08/index.html
4 de novembro de 2016 | 39
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Electromechanical ignition: high-voltage cabling
• Carbon ignition cables
• comprised of a fiberglass core with a silicone interior insulation
• interference suppression resistance results from the carbon cable
resistivity:
• 1 m cable ≈ 10 - 20 kΩ
https://www.ngk.de/en/products-technologies/ignition-cables/
4 de novembro de 2016 | 40
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Electromechanical ignition: high-voltage cabling
• Ignition cables with inductive resistance
• like carbon resistor ignition cables, these ignition cables have a
fiberglass core
• over the fiberglass there is a conductive and magnetic silicone layer,
around which a stainless steel wire is wound
• the cable resistance (reactive inductance)
grows with ignition frequency
(thus, with RPM)
• 1 m cable ≈ 2 - 8 kΩ
https://www.ngk.de/en/products-technologies/ignition-cables/
4 de novembro de 2016 | 41
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Electromechanical ignition: cylindrical coil
https://www.ngk.de/en/technology-in-detail/ignition-coils/design-of-an-ignition-coil/design-of-a-cylinder-ignition-coil/
• Filled with oil
• …
4 de novembro de 2016 | 42
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Electromechanical ignition, transistor-assisted
• An igniter alleviates the circuit breaker job
• primary current is several A and inductive!
• switching it off is a hard job (counter EMF peak between
breaker contacts)
• igniter drives the primary winding, reducing the control current (at
the circuit breaker) to tens of mA, non-inductive
• longer circuit breaker lifetime
• no need for condenser in parallel
• accumulation of dirt in the breaker contacts
… http://what-when-how.com/automobile/electronic-ignition-automobile/
Basic
circuit
4 de novembro de 2016 | 43
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Electromechanical ignition, with igniter and position sensor
• A position sensor substitutes the circuit breaker
• inductive (magnet + pickup coil)
• hall-effect (magnet + hall-effect sensor)
• optical (LED + photodiode or phototransistor)
• Ignition advance is still based on centrifugal and vacuum
mechanisms
• no ECU
… http://www.jetav8r.com/Vision/Ignition/CDI.html
4 de novembro de 2016 | 44
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ECU + distributor with sensing and high-voltage distribution
• Distributor functionalities are restricted to
• sensing crankshaft position/speed
• distributing high-voltage to sparks
• (no mechanical advance)
• ECU functionalities
• receiving position
& speed
sensor data
• computing ignition
timing/duration
• sending ignition timing
signal to ignition coil
… http://www.teglerizer.com/fi/bem/Basics%20of%20engine%20management.htm
4 de novembro de 2016 | 45
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ECU + distributor restricted to high-voltage distribution
• Distributor functionality is restricted to
• distributing high-voltage to sparks
• (just the distributor cap)
• Crankshaft position/speed sensor is located in the flywheel
… http://www.teglerizer.com/fi/bem/Basics%20of%20engine%20management.htm
4 de novembro de 2016 | 46
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Distributorless, 1 coil per 2 cylinders (wasted spark)
• Distributorless = no distributor
• no mechanical parts, no friction, no electric arcs
• Each coil generates two simultaneous sparks
• one is wasted spark at the cylinder ending the exhaust stroke
http://pantera.infopop.cc/eve/forums/a/tpc/f/5650045562/m/1021035995
http://www.teglerizer.com/fi/bem/Basics%20of%20engine%20management.htm
4 de novembro de 2016 | 47
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Distributorless, 1 coil per 2 cylinders (wasted spark)
• Wasted spark, dual tower ignition coil
http://www.tdotperformance.ca/mallory-140052-firestorm-ignition-coil-dual-tower-waste-spark.html
http://www.teglerizer.com/fi/bem/Basics%20of%20engine%20management.htm
4 de novembro de 2016 | 48
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Distributorless, 1 coil per 2 cylinders (wasted spark)
• Wasted spark, but with integrated igniter & coil
• in previous example, igniter is in the ECU
http://www.maxxtuning.eu/products/engine-control-and-electronics/ignition/ignition_coils/ignition-coil-4-cyl-ws-with-integrated-amplifier
http://www.teglerizer.com/fi/bem/Basics%20of%20engine%20management.htm
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Distributorless, 1 coil per cylinder
• Each cylinder/spark has a dedicated coil
• High-voltage wires (from coils to plugs) outside the engine
block
… http://www.teglerizer.com/fi/bem/Basics%20of%20engine%20management.htm
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Distributorless, coil-on-plug
• One coil per cylinder
• no high-voltage wiring
• but primary coil currents travel
outside engine block
http://www.teglerizer.com/fi/bem/Basics%20of%20engine%20management.htm
https://www.ngk.de/en/technology-in-detail/ignition-coils/design-of-an-ignition-coil/design-of-a-pencil-coil-single-spark-coil-coil-on-plug/
4 de novembro de 2016 | 51
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Distributorless, coil-on-plug (with integrated igniter)
A – igniter
B – ignition coil
IGt – ignition timing
IGf – ignition fail
1. primary coil
2. secondary coil
3. voltage protection circuit
4. current protection circuit
5. pulse generator
6. locking circuit
7. amplifier
8. control circuit
http://toyota-club.net/files/faq/04-11-20_faq_az_eng.htm
http://dbnst.nii.ac.jp/english/detail/1784
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Transistorized (inductive discharge) ignition
• TAC – Transistor-Assisted Contacts
• circuit breaker controls T1
• T1 controls T2 (power transistor)
• T2 drives primary current
http://what-when-how.com/automobile/electronic-ignition-automobile/
4 de novembro de 2016 | 53
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Transistorized (inductive discharge) ignition
• Breakerless ignition
• Inductive pickup replaces circuit breaker
http://what-when-how.com/automobile/electronic-ignition-automobile/
4 de novembro de 2016 | 54
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Capacitive discharge electronic ignition
• A capacitor charges with a high voltage (300-500 V)
• Switching device (mechanical breaker or thyristor) triggers
the capacitor discharge over the primary winding
http://www.daytona-twintec.com/tech_ignition.html
4 de novembro de 2016 | 55
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Capacitive discharge electronic ignition
• Capacitor (C) (dis)charge is controlled by a Thyristor (Th)
• Thyristor (Th) ON C discharges on primary winding
http://what-when-how.com/automobile/electronic-ignition-automobile/
4 de novembro de 2016 | 56
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Capacitive discharge electronic ignition
• Charging voltage is achieved through unstable transistor pair
+ full-wave rectifier
http://what-when-how.com/automobile/electronic-ignition-automobile/
4 de novembro de 2016 | 57
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Capacitive vs. Transistorized ignition systems
• CDI very short & very high V spike, constant with RPM
http://www.rotaryeng.net/Why-CDI.html
4 de novembro de 2016 | 58
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Capacitive vs. Transistorized ignition systems
• CDI consumed energy grows linearly with RPM
• XL grows with frequency/RPM
• primary winding XL
• XC decreases with frequency/RPM
• primary winding XL
• charge capacitor XC
http://www.rotaryeng.net/Why-CDI.html
4 de novembro de 2016 | 59
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Capacitive vs. Transistorized ignition systems
• Bottomline, CDI is preferred
• Higher voltage spike
• W proportional to RPM
• But, due to the very short voltage spike
• it requires extremely precise synchronization
• For distributor-based ignition systems, this was problematic
• it required constant tuning
• it was only used in high-performance/race vehicles
• This problem has been overcome with distributorless ignition
systems
• distribution timing is controlled by ECU
• no mechanical tuning is required
http://www.rotaryeng.net/Why-CDI.html
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Technology trends
• …
• …
https://www.newswire.com/press-release/car-alternator-market-global-technical-data-and-growth-2020
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Recommended references
• http://www.superchevy.com/how-to/additional-tech/1601-everything-you-wanted-to-
know-about-vacuum-advance-and-ignition-timing/
• http://www.worldphaco.net/uploads/CAPACITIVE_DISCHARGE_IGNITION_vs_MA
GNETIC_DISCHARGE_IGNITION..pdf/