AN2159 Freescale Semiconductor, Inc. Digital Direct Current

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AN2159 Freescale Semiconductor, Inc. Digital Direct Current

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AN2159
Freescale Semiconductor, Inc.
Digital Direct Current Ignition System Using HC08 Microcontrollers
Kenny Applications Engineering Microcontroller Division Hong Kong
This application note describes reference design engine electronic ignition system, known digital Direct Current Ignition (DCI). system targeted single-cylinder, two-stroke engines such mopeds. heart system Motorola HC08 microcontroller, MC68HC908JK3. text contains brief overview method, description demo circuit constructed laboratory, using MC68HC908JK3 controller. full MC68HC908JK3 specification, please refer data sheet, Motorola order number: MC68HC908JL3/H.
Introduction
past, two-wheelers industry: scooters, motorcycles, mopeds, commonly used engine ignition system based capacitive discharge method, known capacitive discharge ignition (CDI) (described Motorola application note AN4006/D). system saves having battery generate ignition spark thus prolonging battery life. More recently, manufacturers turning alternative method electronic ignition, known Direct Current Ignition (DCI). method sometimes called Inductance Direct Ignition (LDI), because this ignition system uses battery supply current charge inductor, then released high voltage pulse step-up transformer spark plug ignite fuel mixture combustion chamber. Compared with system, system reduces charging
Motorola, Inc., 2001
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Freescale Semiconductor, Inc. Application Note
complexity magneto circuit, thus eliminating high voltages across capacitor during charging periods. method also prolongs system lifetime, since average lifetime high voltage capacitors systems about years. heart this system demo MC68HC908JK3 MCU. 8-bit with 4k-bytes user FLASH memory, ports, analog-to-digital converter, flexible 16-bit timer with input capture output compare functions. Other components used this demo similar that system, without high-voltage capacitor. following sections described demo detail.
Freescale Semiconductor, Inc.
Digital Module
Figure block diagram showing digital module. heart timing control circuit MC68HC908JK3 MCU; monitoring engine speed throttle setting, whilst calculating ignition timing. demo module produces spark necessary ignite air/petrol mixture combustion chamber with variable timing against speed engine. digital module divided into following control blocks: Regulated power supply Analog ignition control Throttle input Signal shaping Advance timing control Ignition circuit
DIGITAL MODULE COIL
BATTERY
REGULATED POWER SUPPLY
SPARK PLUG IGNITION CIRCUIT
PULSER MAGNETO ASSEMBLY
ANALOG IGNITION CONTROL
SIGNAL SHAPING
ADVANCE TIMING CONTROL
THROTTLE INPUT
Figure Digital System Block Diagram
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Application Note Digital Module
Power Supply
from battery stepped down using MC7805 voltage regulator, provides power source controlling circuits. capacitors help maintain steady voltage case sudden voltage transients.
MC78L05
BATTERY
Figure Power Supply
Freescale Semiconductor, Inc.
Signal Shaping
signal shaping circuit designed converting pulses from pulser pulses. circuit uses input voltage comparators with hysteresis characteristics.
VOLTAGE REFERENCE
PULSER
1.5k BRIDGE
PULSE
FROM PULSER, AFTER BRIDGE PULSE
Figure Signal Shaping Analog Ignition Control This analog ignition control circuit designed engine start-up, since wait least engine revolutions initial engine speed. From Figure first pulse switches IGBT (Insulated Gate Bipolar Transistor) charge primary coil second pulse switches IGBT produce high voltage ignition pulse. ignition timing follows signal pulser (Figure Diodes isolate control between analog ignition circuit. Once ready, will isolate analog ignition circuit switching ignition circuit will then directly controlled
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Freescale Semiconductor, Inc. Application Note
IGNITION CIRCUIT FROM SIGNAL SHAPING DISABLE ANALOG IGNITION (FROM MCU)
DIGITAL ADVANCE TIMING (FROM MCU)
Freescale Semiconductor, Inc.
Figure Analog Ignition Control Advance Timing Control heart advance timing control circuit MC68HC908JK3 MCU. main function monitor speed engine throttle setting, calculating optimum ignition time. engine speed determined using MC68HC908JK3's 16-bit timer calculate time interval recurring pulses (from signal shaping circuit) pin. Together with throttle setting input, optimum time ignition pulse calculated. Before ignition spark fired, time required primary coil charge collapsed ignition instance. Therefore, before ignition instance, switch IGBT charge primary coil. ignition instance, switches IGBT. This causes current flowing primary coil collapse, inducing high voltage secondary coil spark plug. should noted that primary coil should charged excessive periods. Long period continuous charging causes primary coil overheat. Therefore, coil should only charged just before ignition pulse required. This charging period controlled MCU. demo, engine speed indicated using external tachometer. This tachometer driven TCH1 pin, configured output, from MC68HC908JK3's timer. pulse width proportional pulses from pulser.
Throttle Control
throttle input simulated using methods. analog throttle simulated using input MC68HC908JK3 monitor variable voltage from potentiometer, Figure With 8-bit ADC, input level divided into steps. alternative method standard MC68HC908JK3 port monitor throttle throttle OFF, Figure
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Application Note Digital Operation
DIGITAL SIGNAL PORT OPTO-COUPLER ANALOG SIGNAL
Analog throttle input
Digital throttle input
Figure Throttle Input
Freescale Semiconductor, Inc.
Ignition Circuit
From Figure prior ignition instance, IGBT switched charge primary coil. ignition instance, IGBT switched off. sudden collapse current flow primary coil produces high voltage pulse across coil. This high voltage pulse then induced step-up secondary coil produce several pulse spark plug. Typically, primary coil 10mH) requires voltage between 400V induce high-voltage secondary coil produce spark distance. Therefore, IGBT must rated handling this voltage.
COIL
BATTERY
SPARK PLUG
IGBT FROM IGNITION CONTROL
Figure Ignition Circuit
Digital Operation
typical operation digital module divided into three modes: Engine start-up: ignition timing provided pulses from pulser. Intermediate engine speeds: Depending throttle setting, ignition advance follows typically curves shown Figure High engine speeds: ignition speed applied with fixed firing angle. This also depends throttle setting.
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Freescale Semiconductor, Inc. Application Note
Ignition Advance Angle (degree)
High
Throttle: 100%
Freescale Semiconductor, Inc.
Speed (RPM 1000)
Figure Example Ignition Advance Characteristics period pulses (positive negative) generated from pulser (mounted magneto) proportional engine speed. pulses then passes through signal shaping circuit converted input level. then captures these pulses calculate output ignition angle. primary coil charged prior ignition pulse. ignition timing diagram shown Figure
Positive pulse (Advance)
Pulser pulses
Negative pulse (Reference pulse)
Filtered pulses Coil charge period Ignition pulses from Switch IGBT Delay value calculated with respect positive pulse (Advance) Time period seconds) Engine Switch IGBT (Ignition instance)
Figure Ignition Advance Waveforms
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Schematics
Freescale Semiconductor, Inc.
MOTOROLA
AN2159
Application Note Schematics
Figure Module Schematics
Freescale Semiconductor, Inc. Application Note
Extra Features
This project demonstrated basic system. Other features, such overcurrent/temperature protection sensor inputs added system fully utilize MC68HC908JK3 MCU. desired features fail safe fall back mechanism failure. failure occurs, system should fall back analog ignition mode, pulses from pulser always present. computer operating properly (COP) module inside MC68HC908JK3 used this purpose.
Freescale Semiconductor, Inc.
Further Information
Reference Design
digital reference design using MC68HC908JK3, with layout source code available from Motorola. Please contact your local Motorola representative further details.
Related Documents
AN4006/D: AN2158/D: AN-HK-33/H:
Digital Capacitive Discharge Ignition System using HC05/HC08 8-Bit Microcontrollers Designing with MC68HC908JL/JK Microcontroller Family In-circuit programming FLASH memory MC68HC908JL3 MC68H(R)C908JL3/JK3/JK1 Technical Data MC68H(R)C08JL3/JK3/JK1 Technical Data
MC68HC908JL3/H: MC68HC08JL3/H:
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. 1-303-675-2140 1-800-441-2447 JAPAN: Motorola Japan Ltd.; SPS, Technical Information Center, 3-20-1, Minami-Azabu, Minato-ku, Tokyo 106-8573 Japan. 81-3-3440-3569 ASIA/PACIFIC: Motorola Semiconductors H.K. Ltd.; Silicon Harbour Centre, King Street, Industrial Estate, N.T., Hong Kong. 852-26668334 Technical Information Center: 1-800-521-6274 HOME PAGE:
Motorola, Inc., 2001
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AN2159 Freescale Semiconductor, Inc. Digital Direct Current

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