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Electronic Engine Management Pt.1: Introduction – by Julian Edgar In some respects, the internal combustion engine which powers cars has barely changed in design over the last 80 years. As far back as the 1920s, some Alfa Romeo engines boasted twin overhead camshafts, six cylinders and supercharging. An engine designer from that early period (if brought back to life!) could look at the internals of a 1993 engine and instantly recognise almost all of the components. So if little fundamental mechanical change has occurred, why has the under-bonnet view of a typical car undergone such a dramatic change over the last 10 or 15 years? Engine management The answer to that question includes A BMW Motronic electronic control module. All modern cars make extensive use of electronic circui­try to control engine functions, to ensure maximum performance & economy. 8  Silicon Chip aspects like pollution control plumbing and the use of front-wheel drive. However, a major part of the change has been in the use of electronic engine management techniques. Electronic engine management is responsi­ble for governing fuel induction and ignition timing in all current cars, as well as controlling more exotic aspects in some machines like camshaft timing, turbocharger boost, inlet manifold tuning and automatic transmission control. The accuracy and resolution of these electronic control mechanisms has greatly improved the efficiency of the internal combustion engine, while the use of ram-tuned intake manifolds (which engine management allows) has revolutionised engine ap­pearance. In many ways, a current automotive engine is a strange mix of old mechanical technology and the very latest in electron­ic control techniques. The effectiveness of this approach can be seen by comparing an electronically-controlled engine with an engine produced 25 years ago. The examples contrasted here are the 1.8-litre overhead cam (OHC) engine used in the old Datsun 180B and the 1.8-litre OHC engine used in the 1988 GM Holden Astra. The old Datsun 180B engine used a single carburettor to control fuel/air mixing, with points, weights, springs and a vacuum canister controlling THROTTLE BODY FUEL PRESSURE REGULATOR CONTROL SOLENOID VALVE OXYGEN SENSOR THROTTLE VALVE SWITCH AUXILIARY AIR CONTROL VALVE FAST IDLE CONTROL DEVICE FUEL PRESSURE REGULATOR AIR FLOW METER AIR REGULATOR ROTOR PLATE COOLANT TEMPERATURE SENSOR CRANK ANGLE SENSOR INJECTOR IGNITION COIL Fig.1: this diagram shows the locations of the main components in the Holden VL Commodore engine management system. ignition timing. As Table 1 shows, power, torque, performance and fuel economy are all greatly improved in the engine-managed car, despite the fact that the mechanical design of the engines is very similar. Note that the power and torque figures for the Datsun are based on the then-current SAE system of measurement – widely regarded as being 10-15% optimistic compared to current DIN measurement standards. What is not shown by the table is that the modern car runs on unleaded fuel of a lower octane rating than the super petrol used in the older design. Exhaust gas pollutants are also much lower in the engine-managed car. Advantages Electronic engine management gives advantages over the use of carbies and conventional ignition TABLE 1 1972 Datsun 180B 1988 Holden Astra Type 4-door sedan 4-door sedan Mass 1000kg 1020kg 4-cylinder, in-line 4-cylinder, in-line Body Engine Type Volume 1770cc 1796cc 2-barrel carb. multi-point EFI Power* 78kW 79kW Torque* 146Nm 151Nm Induction POWER TRANSISTOR timing control in the fol­ lowing areas: power, torque, fuel econ­omy, engine responsiveness and exhaust gas emissions. Much to the surprise of early sceptics, electronic engine management has also proved to be very reliable in the field. This is partly because most engine management systems feature “limp-home” modes, which come into effect if a breakdown occurs in the system. In one BMW model, “limp-home” is a relative term – a top speed of 200km/h is allowed while lame! Electronic fuel injection Performance 0-100km/h 12.4 secs 11.0 secs Standing 400m 18.4 secs 17.6 secs Top Speed 165km/h 185km/h 11 litres/100km 8 litres/100km Fuel Economy * Datsun 180B figures use SAE measurement; Astra use DIN. Engine management systems used to be referred to as “elec­tronic fuel injection” (EFI) systems. Early fuel injection sys­tems were mechanical in nature but were quickly replaced with electronically-controlled injection. Initially, the fuel system remained entirely separate from the October 1993  9 then realised. As a result, all modern cars now run combined electronic fuel injection and ignition systems, thus giving rise to the overall term of “engine manage­ment”. Inputs & outputs Electronic engine management gives major power, economy & drive­ability advantages compared to carburettors, even sophisti­cated units like this Weber. ignition system. In fact, some early fuel injected cars ran an electronically-controlled injection system alongside an old points-and-weights Kettering ignition system. The 1974 BMW 3.0si, for example, ran an injection-only system – which still gave a 15kW power gain over the twin-carby version of the same engine. Manufacturers – with Bosch being the prime mover in the automotive electronics area – soon realised that the sensors being used to monitor the engine for the EFI system could also be used to determine ignition timing. The extra complexity and expense was relatively minor compared with the potential advan­tages which could be CRANK ANGLE SENSOR AIR FLOW METER FUEL INJECTION INJECTORS IGNITION TIMING CONTROL POWER TRANSISTOR IDLE SPEED CONTROL AUXILIARY AIR CONTROL VALVE FUEL PUMP CONTROL FUEL PUMP FUEL PRESSURE FUEL PRESSURE REGULATOR CONTROL SOLENOID VALVE SELF-DIAGNOSIS INSPECTION LAMPS COOLANT TEMPERATURE SENSOR IGNITION SWITCH THROTTLE VALVE SWITCH BATTERY VOLTAGE ECCS CONTROL UNIT AIR CONDITIONER SWITCH VEHICLE SPEED SENSOR OXYGEN SENSOR PARK/NEUTRAL SENSOR Fig.2: inputs & outputs of the VL Commodore engine management system. The inputs are monitored by the control module which then controls the various engine parameters. 10  Silicon Chip All engine management systems can be analysed in terms of their inputs and outputs to and from the computer, or Engine Control Module (ECM) as it is referred to in automotive circles. Fig.2 shows a typical system, as used in the Holden VL Commodore 6-cylinder (Nissan) engine. Each input on the lefthand side of the diagram is used to sense a different engine operating parame­ter. For example, the Crank Angle Sensor indicates to the ECM where the crankshaft is in its rotation. This sensor is often mounted within the distributor. Another sensor known as the Airflow Meter indicates, by means of a varying voltage signal, the mass of air passing into the engine. And, as its name im­plies, the Coolant Temperature Sensor tells the ECM whether the engine is cold or hot. One of the more obscure inputs is the exhaust gas Oxygen Sensor, which compares the concentration of oxygen in the air with that in the exhaust gases, and indicates to the ECM the fuel/air mixture strength. The Battery Voltage is also used in some systems as one of the idle-speed control inputs – if the battery voltage is too low, then the ECM increases the idle speed to help recharge the battery! The outputs from the ECM in this relatively simple approach control mainly fuel injector pulse width and ignition timing. The fuel pressure in this system can also be electrically controlled – generally, it’s controlled mechanically by a pressure regula­tor. In this particular car, fuel pressure is increased during cranking if the engine coolant temperature is above 95°C. This prevents vapour-lock problems during hot starting. The Self Diagnosis function is very important. Because of the complexity in finding loom and sensor faults, almost all systems run a self-diagnosis output. When activated, this indi­cates codes which show that the system is fine, or that problems exist with certain sensors or wiring. In the Nissan system shown here, two LEDs mounted in the ECM box flash the codes. Other manufacturers This turbocharged, intercooled, four-valves-per-cylinder, 2-litre Subaru flat four engine has a maximum power output of 147kW. Without modern engine management techniques, such an engine would be impossible. use a “Check Engine” light mounted on the dashboard as the communications interface. Early EFI systems often didn’t have a self-diagnosis capability, which makes fault-finding much more difficult. Performance & economy An example of an engine management input sensor. This crankshaft position sensor is mounted at the end of one of the camshafts & uses an optical sensor to monitor the slots & holes cut into the spinning endplate. As an example of the upper extreme in current engine man­agement techniques, the Subaru Liberty RS Turbo uses a system with 14 input sensors and 12 output signals. A self-learning air/fuel mixture mode is used, where individual driving styles and engine wear are internally catered for. Separate coils di­rectly mounted on each spark-plug are used and a 3-dimensional ignition advance map is employed. The power output from the engine is 147kW and the 4-door car will acceler­ate to 100km/h in 6.7 seconds – faster than any of the tradition­al Australian “muscle car” V8s. This level of performance – matched with economy – from a 2-litre 4-cylinder engine would be simply impossible without full electronic engine manSC agement. October 1993  11