AN4006 Digital Capacitive Discharge Ignition System using HC05/HC

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AN4006 Digital Capacitive Discharge Ignition System using HC05/HC

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AN4006
Digital Capacitive Discharge Ignition System using HC05/HC08 8-Bit Microcontrollers
Freescale Semiconductor, Inc.
Kenny Market Development Transportation Systems Group Asia Pacific Region
This application note describes basic principle digital capacitive discharge Ignition (CDI) system two-wheelers, outlines solution using Motorola's low-cost MC68HC705P6A microcontroller unit.
Introduction
two-wheelers industry: scooters, motorcycles, mopeds, commonly engine ignition system based capacitive discharge method, known Capacitive Discharge Ignition (CDI). This ignition system makes energy transferred from magneto storage capacitor, then released high voltage pulse step-up transformer spark plug ignite fuel mixture inside cylinder. Using this method saves having battery generate ignition spark thus prolonging battery life. Today, demand more efficient engine designs government regulations pollution control, with variable timing becoming most economical choices available. This variable timing achieved using MCU, such Motorola's low-cost MC68HC705P6A. This equipped with 16-bit timer with independent input capture output compare functions. following text describes traditional solution digital solution using microcontroller unit.
Motorola, Inc., 2000
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Ignition System
ignition system functions provide high voltage spark each engine's cylinders ignite air-fuel mixture. This high voltage spark must distributed ignition timing each cylinders just right moment power stoke. Traditionally, timing single-cylinder two-wheeler fixed, known fixed-time CDI. timing high voltage spark fixed every piston cycle. Because time from ignition combustion cylinder instantaneous, spark timed occur before compression stroke order combustion completed time drive piston downwards power stoke.
Freescale Semiconductor, Inc.
Early Ignition
This fixed timing spark drawbacks. During engine idling speeds, ignition will occur early during compression stoke, combustion will completed before piston reaches top-dead-center position. piston tries complete compression stroke against high pressure, resulting engine stall kick-back when being started flywheel momentum cannot overcome pressure. This noticeable with audible detonating knock. This untimely detonation, together with overheating cause damages piston. other end, during high engine speeds, ignition will occur late during compression stoke, combustion will completed until piston some along power stoke. pressure that propels piston will reduced, resulting loss power. With variable timing solution, speed engine monitored provide optimum timing spark. idling speeds, ignition timed occur quite late compression stroke since there enough time combustion completed piston starts power stroke. high speeds, ignition must occur earlier compression stoke. variable timing system implemented mechanical electronic methods. electronic solution make uses microcontroller (MCU) monitoring engine speed providing accurate timing spark. Another advantage using that ignition spark made occur anytime particular engine speed. Therefore ignition angle fully customized different engine designs. Having perfect ignition timing will increase engine efficiency, save energy, less pollution.
Late Ignition
Advantages Digital
Basic Components Two-Wheelers
also called thyristor ignition system. system with induction type pulse generator contains trigger box, charging device, pulse shaping circuit ignition transformer. main components shown below.
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MOTOROLA
Magneto
small two- four-stroke single dual cylinder engine flywheel, incorporating permanent magnets. rotor, consisting copper coil, produces voltage between 100V 400V, proportional speed engine. After rectification, this high voltage applied capacitor portion. magneto also known alternator, figure
MAGNETO
PULSER
Freescale Semiconductor, Inc.
Figure Magneto/Pulser Assembly
Pulser
pulser small coil mounted magneto, that generates alternating pulse while engine rotates. These pulses induced from poles magnetic plate that mounted framework magneto while rotates passes pulser coil. poles induces positive pulse followed negative pulse that typically mechanical degrees apart. degrees fixed length magnetic plate. peak negative pulse taken reference point, top-dead-center piston. Therefore, positive pulse leads negative pulse mechanical degrees.
Ignition Coil
ignition coil step-up transformer, which delivers high voltage spark plug. This high voltage between 20kV, depending working conditions.
Figure Ignition Coil
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Spark Plug
spark plug final element ignition chain. High engine efficiency complete combustion linked good quality spark. Generally, estimated minimum milli-joules necessary spark plug produce sufficient spark.
Figure Spark Plug
Freescale Semiconductor, Inc.
Digital Module
Figure block diagram showing typical digital module. heart timing control circuit MCU; monitoring engine speed calculating timing spark.
MAGNETO ASSEMBLY SUPPLY IGNITION ANALOG IGNITION CONTROL CIRCUIT DIGITAL MODULE COIL
SPARK PLUG
PULSER
POWER SUPPLY
SIGNAL SHAPING (FILTERING) ADVANCE TIMING CONTROL
Figure Typical Digital System Block Diagram digital module divided into following control blocks, following paragraphs describe function each block: Analog ignition control Power supply Signal shaping (filtering) Advanced timing control (MCU) Ignition circuit block
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Analog Ignition Control
FROM PULSER FROM IGNITION CIRCUIT
FROM
Figure Analog Ignition Control This Analog Ignition Control designed engine start-up stage, since supply ready during engine cold starts. During this start-up stage, ignition timing follows signal pulser. figure limit current Ignition Circuit. Diodes prevent interference between Analog Ignition Control. will turn Analog Ignition Control turning once ready. Then, Ignition Circuit will directly controlled itself.
Freescale Semiconductor, Inc.
Power Supply
HALF-WAVE BRIDGE MC7805
Figure Power Supply magneto provides, after rectification, regulated supply entire module variable timing ignition control. figure half-wave bridge supply negative phase from magneto digital board. resistor, current limiter. zener, which absorbs excessive power from supply while magneto running high speeds, maintain input MC7805. also perform dummy load, which counter-balance load positive phase charge Ignition Circuit. This helps reduce engine vibration. capacitor, will charge potential maximum value (approximately 15V). stores this potential, since leakage path exists; diode half-wave bridge does pass positive current. diode resistance infinite inverse direction, charge flow during this portion cycle. result, input MC7805 maintained
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Signal Shaping (Filtering)
OPTO-COUPLER
FROM PULSER
Figure Pulse Shaping figure opto-coupler performs filtering spikes occurring sensor signal. also converts analog pulses into digital pulses MCU. period pulses determined engine.
Freescale Semiconductor, Inc.
Advanced Timing Control (MCU) Ignition Circuit
heart advance timing control block MCU. This takes reference pulses generated pulser calculates firing angle based engine speed.
FROM SUPPLY FIRING CONTROL COIL
Figure Advance Timing Control figure diode, conducts forward current charging capacitor. When spark required, current from Advanced Timing Control injected into gate, firing firing initiates discharge capacitor, which generates current transfers primary winding ignition coil. conducts during first part current cycle until capacitor voltage reaches secondary coil induces high voltage (typically 14kV) while current passes through primary coil. spark plug then generates spark from high voltage. Typically, with value somewhere between 0.47 stores charge from magneto supply, which provides, after rectification, positive voltage.
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MOTOROLA
Digital Operation
typical operation digital module divided into three modes: engine speeds: ignition spark applied detection negative sensor pulse (zero degrees; piston top-dead-center). High engine speeds: ignition spark applied detection positive sensor pulse degree advance). Intermediate engine speeds: Between high speeds, ignition advance angle directly proportional engine speed. Figure illustrates ignition advance angle different engine speeds.
Freescale Semiconductor, Inc.
Ignition Advance Angle (degree)
High
Speed (RPM 1000)
Figure Ignition Advance Characteristics Principle Operation pulses from pulser captured isolation circuit (the pulse shaping circuit). From pulses uses 16-timer count period between pulses determine engine speed. ignition advance angle then calculated outputs required pulse ignition circuit. Figure shows input output pulses.
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Pulser pulses
Positive pulse (Advance)
Negative pulse (Reference pulse)
Filtered pulses
Ignition pulses from
Freescale Semiconductor, Inc.
Delay value calculated with respect positive pulse (Advance) Time period Engine sec)
Figure Ignition Advance Waveforms
Further Information Digital Reference Design
digital reference design, using Motorola's MC68HC705P6A MCU, with circuit schematics, layout, source code available from Motorola. Please contact your local Motorola representative further details.
Motorola reserves right make changes without further notice products herein. Motorola makes warranty, representation guarantee regarding suitability products particular purpose, does Motorola assume liability arising application product circuit, specifically disclaims liability, including without limitation consequential incidental damages. "Typical" parameters which provided Motorola data sheets and/or specifications vary different applications actual performance vary over time. operating parameters, including "Typicals" must validated each customer application customer's technical experts. Motorola does convey license under patent rights rights others. Motorola products designed, intended, authorized components systems intended surgical implant into body, other applications intended support sustain life, other application which failure Motorola product could create situation where personal injury death occur. Should Buyer purchase Motorola products such unintended unauthorized application, Buyer shall indemnify hold Motorola officers, employees, subsidiaries, affiliates, distributors harmless against claims, costs, damages, expenses, reasonable attorney fees arising directly indirectly, claim personal injury death associated with such unintended unauthorized use, even such claim alleges that Motorola negligent regarding design manufacture part. Motorola registered trademarks Motorola, Inc. Motorola, Inc. Equal Opportunity/Affirmative Action Employer.
reach USA/EUROPE/Locations Listed: Motorola Literature Distribution; P.O. 5405, Denver, Colorado 80217. 1-800-441-2447 1-303-675-2140 JAPAN: Nippon Motorola Ltd. SPD, Strategic Planning Office 4-32-1, Nishi-Gotanda, Shinagawa-ku, Tokyo 141, Japan. 03-5487-8488 MfaxTM, Motorola Back System: RMFAX0@email.sps.mot.com; http://sps.motorola.com/mfax/; TOUCHTONE 1-602-244-6609; Canada ONLY 1-800-774-1848 HOME PAGE: http://motorola.com/sps/
Mfax trademark Motorola, Inc. Motorola, Inc., 2000
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AN4006 Digital Capacitive Discharge Ignition System using HC05/HC

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