M.S Ramaiah School of Advanced Studies - Bangalore

Engine Control (Gasoline Engine) Lecture delivered by: Prof. Ashok C.Meti MSRSAS-Bangalore Session objectives To understand the need for EMS, its configuration, specifications of components. To study the various control actions fuel control, ignition control and other control strategies implemented in EMS. To understand the role of embedded software and OBD. 1

Topics Introduction to Electronic engine control Typical configuration of EMS Fuel delivery systems Exhaust emission Fuel control Ignition control OBD Introduction Electronic Engine Control Objectives of Electronic Engine Control Minimize exhaust emissions Minimize Fuel consumption Provide optimum driveability for all operating conditions Minimize evaporative emissions Provide system diagnosis when malfunctions occur 2

The electronic engine control system consists of Sensing devices continuously measure the operating conditions of the engine Electronic control unit (ECU) evaluates the sensor inputs using data tables, calculates and determines the output to the actuating devices. Actuating devices commanded by ECU to perform an action in response to sensor inputs. Typical configuration of an EMS 3

Components in EMS An ECU might contain a 32-bit, 40-MHz processor. The code in an average ECU takes up less than 1-2 megabyte (MB) of memory. The processor is packaged in a module with hundreds of other components on a multi-layer circuit board. ECU Some of the other components in the ECU that support the processor are: Analog-to-digital converters Digital-to-analog converters High-level digital outputs Signal conditioners Communication chips 4

Typical output drivers in the ECU usually supply a ground for the actuator solenoids and relays Fuel Delivery Systems Fuel management consists of metering the fuel, formation of the air/fuel i/f mixture, transportation tti of fthe mixture, and dditib distribution ti of fthe air/fuel mixture. The fuel delivery systems must provide the proper quantity of fuel to create a combustible mixture in the engine cylinder. There are two fuel delivery system configurations: Single-point fuel injection Multipoint fuel injection 5

Exhaust Emissions Exhaust Components The engine exhaust consists of the products of combustion of air and fuel mixture. Fuel is a mixture of chemical compounds termed hydrocarbons(hc) Under perfect combustion conditions, the hydrocarbons would combine in a thermal reaction with oxygen in the air to form carbon dioxide (CO 2 ) and water (H 2 O) Unfortunately, perfect combustion does not occur and in addition to CO 2 and H 2 O, carbon monoxide (CO), oxides of nitrogen (NO x ), and hydrocarbons occur in the exhaust as a result of the combustion reaction. Additives and impurities in the fuel also contribute small quantities of pollutants such as lead oxides, lead halogenides and sulfur oxides. In CI engines, there is also considerable amount of soot ( particulates) generated. Spark Ignition Engines Air/Fuel Ratio mass ratio of air to fuel. For a spark ignition, the mass ratio for complete fuel combustion is 14.7:1. (I.e 14.7 kg of air to 1 kg of fuel) This ratio is known as Stoichiometric ratio. This is approximately 10000 liters of air for 1 liter of fuel 6

Lambda- λ Sometimes, the air/fuel ratio is described in terms of excess-air factor known as Lambda(λ). It indicates the deviation of the actual air/fuel ratio from the theoretically required ratio: Quantity of air supplied Theoretical requirement (14.7 for petrol) At stoichiometry λ = 1 For a mixture with excess air (Lean mix): λ >1 For a mixture with deficient air (rich mix): λ <1 CO emissions: In the rich operating range(λ <1), CO emissions increase almost linearly with an increasing amount of fuel. In the lean range(λ >1), CO emissions are at their lowest. HC Emissions As with CO emissions, HC emissions increasing amount of fuel. The minimum HC emissions occur at λ =1.1 1.2. At very lean air/fuel ratios, the HC emissions again increase due to less than optimal combustion conditions resulting in unburnt fuel. NO x emissions The effect of the air/fuel ratio on NO x emission is opposite of CO and HC emission on the rich side of stoichiometry. As the air content increases, the oxygen content increases and the result is more NO x. On the lean side of stoichiometry, NO x emissions decrease with increasing air because the decreasing density lowers the combustion chamber temperature. The maximum NO x emission occur at λ =1.05.. 1.1. 7

Catalytic converters A catalytic converter in the exhaust system is used to reduce (about 90%) the exhaust gas emissions concentration. Chemical reactions occur in the converter that transform the exhaust emission to less harmful chemical compounds. For spark ignition engines, most commonly a three-way converter (TWC)is used. The TWC reduces the concentrations of CO, HC and NO x by converting them into CO 2, and H 2 O and N 2 For maximum efficiency for conversion, the average air / fuel ratio must be maintained within less than 1 % of stoichiometry. This small operating range is known as the Lambda window or Catalytic converter window. To remain within the catalytic converter window, the air/fuel ratio is controlled by the Lambda closed-loop loop fuel control system which is part of the electronic engine control system. 8

Ignition Timing It is defined as the crank angle before top dead center(tdc) at which the ignition spark occurs. It has a decisive effect on the exhaust emissions. CO emissions are almost completely independent of the ignition timing and mainly a function of the air/fuel ratio In general, more the ignition advance, higher emissions of HC. With increased timing advance, there is an increase in NO x emission regardless of air/fuel ratio. Precise control of ignition timing is required to provide optimal exhaust emissions. Ignition timing is generally controlled by the ECU. Exhaust Gas Recirculation (EGR) A method to reduce emissions of oxides of nitrogen. A portion of exhaust gas is re-circulated back to the combustion chamber. The exhaust gas is an inert gas and, in the combustion chamber, it lowers the peak combustion temperature. Depending upon the amount of EGR, NO x emissions can be reduced by up to 60%, although an increase in HC emissions would occur at such high levels of EGR. 9

A system links the exhaust manifold to the intake manifold through a metering by a pneumatic or electronic valve. The ECU controls the valve. The amount of EGR is limited by- An increase in HC emission Fuel consumption Engine roughness Fuel Consumption Federal statutes are currently in effect that require each automobile manufacturer to achieve a certain average fuel economy for all their models produced in one model year. The electronic engine control system provides the fuel metering and ignition timing precision required to minimize the fuel consumption. Optimum fuel economy occurs near λ =1.1. However, lean engine operation affects exhaust emissions and NO X is at its maximum at λ =1.1 10

During coasting and braking, fuel consumption can be further reduced by shutting off the fuel until the engine speed decreases to slightly higher than the set idle speed. The ECU determines when fuel shutoff can occur by evaluating the Throttle position Engine RPM Vehicle speed The influence of ignition timing on fuel consumption is the opposite of its influence on exhaust emissions. A sophisticated ignition control strategy is implemented by the ECU to reach a compromise between the fuel consumption and emissions at all operating conditions. Driveability Another requirement of the electronic engine control unit to provide acceptable drivability under all operating conditions. That is - no stalling of engine, Hesitations, and other objectionable roughness should occur during vehicle driving. The driveability is influenced by every operation of the engine control system. A significant contribution is from fuel metering and ignition timing. Other factors influence the driveability are- idling speed control EGR control evaporative emissions control. 11

Evaporative Emission Control Federal statutes closely regulate the HC emissions from the fuel vapors escaping from the vehicle. Fuel tank is the prime source. Causes for vapors in the fuel tank: Increasing ambient temperatures Return of unused hot fuel from the engine The evaporative emissions control system routes the fuel vapor to the intake manifold to burn the vapors and control HC emissions. The quantity of the fuel vapor delivered to the intake are metered such that exhaust emissions and dirveability are not affected. The metering is provided by a purge control valve which is under ECU control. Engine Control Functions Fuel Control Assumption: To understand the fuel control strategy, a multipoint pulsed injection is assumed. To decide the amount of fuel to be admitted, the mass flow rate of the incoming air(also known as air charge) to be determined. Am Fm requested air - fuel ratio Where F m = fuel mass flow rate A m = air mass flow rate The air mass flow rate can be calculated from: A m = A v A d Where A v = volume flow rate of intake air A d = air density 12

There are three methods commonly used for determining the air charge: 1. Speed density Air charge is calculated by the engine ECU based on measurement of Air inlet temperature Intake manifold pressure Engine RPM The pressure and temperatures are used to determine the air density and RPM for determining volume flow rate. The calculated volume flow rate during suction stroke: RPM D A RPM V E 60 2 Where, RPM = engine speed, D= engine displacement and V E = volumetric efficiency In an engine with EGR, the volume flow rate of EGR must be subtracted from the calculated volume flow rate. A A A v RPM EGR 2. Air flow measurement Air flow is measured using a vane type meter. Air density changes are compensated by an air inlet temperature sensor. The vane meter uses a the force of incoming air to move a flap through a dfi defined dangle. This angular movement is converted to a voltage ratio by a potentiometer. Because only fresh air charge is measured, no compensation is required for EGR. 3. Air mass measurement The air charge is measured directly using a hot wire or hot-film air mass flow sensor. The inlet air passes a heated element. The element is part of a bridge circuit it that keeps the element at a constant temperature above the inlet air temperature. By measuring the heating current required by bridge circuit and converting this to a voltage via a resistor, the air mass flow passing the element can be determined. Because only fresh air charge is measured, no compensation is required for EGR. 13

Injector pulse width calculation The base pulse width is calculated from the fuel mass flow rate (F m ) and an empirical injector constant. The injector constant is determined by the design of the injector and dis a function of energized time versus the flow volume. This constant is normally determined with a constant pressure differential pressure across the injector. If the pressure across the injector does not remain constant,an entire map of injector constants for different manifold pressure may be required. The effective injector pulse width is a modification of the base pulse width. It is adjusted by a number of correction factors depending upon the operating conditions. For example: Battery voltage correction is required to compensate for the electromechanical characteristics. Other common correction factors may include- Hot restart Cold operation Transient operation corrections 14

DETERMINATION OF EFFECTIVE INJECTOR PULSE WIDTH BASE PULSE WIDTH CALCULATED FROM (F m ) LOAD SIGNAL PULSE WIDTH DURING CRANKING 0 (AFTER START) AND WARM-UP CORRECTION LAMBDA CONTROL CORRECTION WITH ACTIVE LAMBDA CONTROL COASTING RPM / VEHICLE SPEED LIMIT REACHED? NO TRANSIENT COMPENSATION YES FUEL CUT-OFF CORRECTION FOR NO LOAD LOAD TRANSITION OPERATION DEPENDENT PULSE WIDTH CORRECTION BATTERY VOLTAGE CORRECTION EFFECTIVE PULSE WIDTH Injection strategies 3 commonly used strategies: Simultaneous injection Injection of fuel occurs at the same time for all cylinders every revolution of the crankshaft. Therefore, fuel is injected twice within each four-stroke cycle. cle Injection timing is fixed with respect to crank/cam shaft position. Group injection The injectors are divided into two groups that are controlled separately. Each group injects once per four-stroke cycle. The offset between the groups is one crankshaft revolution. This allows for injection timing selection that eliminates spraying fuel into an open intake valve. Sequential injection Each injector is controlled separately. Injection timing, both with reference to crank/camshaft position and pulse width, can be optimized for each individual cylinder. 15

Lambda Control A sub system of the fuel control system working in closed-loop. The lambda sensor or exhaust gas oxygen sensor is installed in the engine exhaust stream upstream of the catalytic converter. This sensor responds to the oxygen content in the exhaust gas and the sensor signal acts as a feedback to the fuel control system. The sensor signal provides for the optimal tuning required to remain in the catalytic converter window for optimum performance. Sensor output: For a lean mixture( λ >1), the sensor output is approximately 100mV For a rich mixture( λ <1), the sensor output is approximately 800mV At roughly λ =1, the output voltage switches between the two voltages. This sensor signal is used to modify the base pulse width to achieve λ =1. The lambda sensor has to reach the operational temperature after which the lambda control loop becomes active. The ECU monitors the sensor signal to determine when the sensor is supplying usable information. An active sensor signal along with the other requirements, such as engine temperature, must be achieved before the lambda control-loop will be activated. 16

Steady sate conditions: Control system oscillates between rich and lean around the lambda window. As the lambda sensor switches, the injector pulse width is adjusted by the amount determined by a control factor until the lambda sensor switches again to the opposite condition. The frequency of oscillation is determined by the gas transport time and magnitude of control time. Transient conditions: The gas transportation time results in a delay before the lambda sensor can indicate that the operating conditions have changed. Using only the lambda sensor for closed loop fuel control would result into poor driveability and exhaust emissions due to this delay. Therefore, an anticipatory control strategy is adopted that uses the engine load and RPM to determine the approximate fuel requirement. The ECU contains the data maps for different combinations of load and RPM. This allows for rapid response to changes in operating conditions. Using system modeling and engine development testing the data for the data tables would be generated and stored in ECU 17

Ignition control The goal is to provide spark advance which optimizes- engine torque exhaust emissions fuel economy driveability and minimize the engine knock. The data tables with the base ignition timing, depending upon the engine load and speed are developed through the engine testing and stored in the ROM of ECU. Corrections to the base timing values are needed for Temperature effects EGR Hot restart Barometric pressure Engine knock. In some case, some systems use ignition timing to vary the engine torque for improvement in automatic shift quality or for idle speed control. 18

Determination of effective ignition timing BASE IGNTION TIMING FROM LOAD AND RPM SIGNAL TEMPERATURE CORRECTION (AFTER START) AND WARM-UP CORRECTION COASTING (NO LOAD)? IGNITION CORRECTION BASED ON OPERATION CONDITION 0 NO YES CORRECTION FOR NO LOAD FUEL CUT-OFF CORRECTION FOR NO LOAD LOAD TRANSITION IGNITION TIMING FOR IDLING CONTROL CORRECTION FOR TRANSMISSION SHIFT 0 IGNITION TIMING FOR KNOCK CONTROL IGNITION ANGLE LIMIT EFFECTVE IGNITION TIMING Dwell angle control The dwell angle performance map stored in the ECU controls the charging time of the ignition coil, depending di on RPM and btt battery voltage. The dwell angle is controlled so that the desired primary current is reached at the end of the charging time just prior to the ignition point. This assures the necessary yprimary current, even with quick transients in RPM. A limit on the charge time in the upper RPM ranges allows the necessary spark duration. 19

Knock Control The ignition timing for optimization of Torque Fuel economy Exhaust emissions is in the close proximity to the ignition timing that results in knocking. Engine knock occurs when the ignition timing is advanced too far for the engine operating conditions and causes uncontrolled combustion that can lead to engine damage, depending on the severity and frequency Other factors that contribute to knock- Quality of fuel Variations in compression ratio The knock sensors (accelerometers) are installed to detect the engine knock. The ECU gets the signals from these sensors. ECU determines from these signals which cylinder or cylinders are knocking. Control action: Ignition timing is modified (retarded) for those cylinders until the knock is no longer detected. The ignition timing is then advanced again until knock is detected. 20

Engine Control Modes Engine Crank and start Engine Warm up Transient Compensation Acceleration enrichment Deceleration Enrichment Full Load Idle Speed Control Role of Embedded Software The engine operation is a complex operation involving thousands of variables, hundreds of controlled parameters. The codes need to be developed addressing all the operational requirements of the engine. The execution speed is critical as the engine speeds are on the rising. It is required to be optimized for speed and size. Thorough tests at different stages is most important and HIL is quite useful in calibration and fine tuning. As several controllers are used in various systems and subsystems, communication and data sharing is most essential for each of the systems 21

Software Development Process- Ford Embedded System Development Sequence Software Code Development Compile and get error-free output file in hex format. Download the program into the ROM of the Target hardware or on to the Emulator (RAM Area) Run the code from the actual Target or from the Emulator. Debug the code. Make code changes to fix the bugs. Recompile and repeat the above process till all bugs are fixed and the code is error free. Use the error-free code for manufacturing many numbers of the same product. 22

DATA Maps / Tables Fueling Map Engine Knock Limits Electronic Ignition Control based Mechanical Advance Mechanism based Timing Map On-board Diagnostics The increasing complexity of vehicle technology led manufacturers to develop ways to effectively diagnose vehicle problems as a result of new electronic hardware. OBD I Simple connectivity and pass/fail checks (Did not cover monitoring Catalytic converter, EEC, engine misfire,etc) 23

On Board Diagnostics - II Generally, OBD-II (applied 1996 and later) has the ability to Detect component degradation or faulty emission related system that prevents compliance with emission standards. Alert the driver of needed emission-related repair or maintenance Use standard ddtcs and general scan tools. As per the OBD-II requirements, the vehicle computer must be capable of testing for, and determining, if the exhaust emissions are within 1.5 times the limits. Thus, computer must do the following- Test all exhaust emission components for correct operation Actively operate the system and measure the results Monitor the engine operation to be certain that the exhaust emissions are within the 1.5 times the limits Check for misfire Turn on the MIL if fault is detected in a circuit or system Record freeze frame at the time the DTC was set Flash the MIL if an engine misfire ocurs that could damage the catalytic converter 24

Monitors Monitor is a organized method of testing specific part of the system. These are test t that t the computer performs to evaluate the components and systems Two types of monitors Continuous monitors Non-continuous monitorsλ As required conditions are met, continuous monitors begin to run. There are continuous monitors- 1. Comprehensive component monitor (CCM) watches the sensors and actuators in the OBD-II system Some of the components tested by the CCM include- Camshaft (CMP) and crankshaft (CKP) sensors Engine coolant temperature (ECT) sensor EVAP purge switch or sensor Inteke air temperature (IAT) sensor Knock sensor (KS) Manifold absolute pressure (MAP) sensor Mass air flow (MAF) sensor Throttle position (TP) sensor Vehicle speed (CS) sensor Idle air control (IAC) solenoid Ignition control system 25

2. Misfire monitor Monitor the engine misfire. It compares acceleration of firing event and determines if a cylinder is not firing correctly 3. Fuel monitor the computer monitors short- term fuel (STFT) and long-term fuel trim (LTFT). Constantly updated adaptive fuel tables are stored in NV RAM and used by the computer for compensation due to wear and aging of the fuel system components. Fuel trim is expressed as ±% and represents the amount of fuel different from the anticipated amount. Non-continuous monitors run once per vehicle drive cycle. Some of fthem are- O2S monitor O2S heater monitor Catalyst monitor EGR monitor EVAP monitor and so on 26

Various diagnostic strategies can be applied to sensors and actuators One such strategy to detect sensor circuit failure is shown below: ADC Conversion Value Coolant Temperature Sensor ADC CPU 0.15<ADC value<4.85v No Yes Failure Judged Use Oil Temperature To Engine Control routine M.S ECM Ramaiah School of Advanced Studies - Bangalore OBD Testers Portable, user friendly OBD diagnosis of control units with ISO* and SAE* protocols. Can test any automobile with OBD Integrated Thermal Printer 27

Single J1962 connection to all OBDII compliant vehicles, providing both power and communications. Support for J1979 E/E Diagnostic Test modes 1 through 7. Communication via SAE J1850 PWM, SAE J1850 VPW, ISO 9141-2 and ISO 14230-4 protocols. Automatic detection and selection of relevant protocol. Plug-in program cartridge for compatibility with future requirements. Power-on self test routine Another Example Diagnostic Trouble Codes - DTC 28

Summary The complete EMS for a gasoline engine has been discussed in terms of - need for EMS, its configuration, specifications of components. Various control actions fuel control, ignition control and other control strategies implemented in EMS have been discussed The role of embedded software and OBD have been explained. 29