Engine Control Unit
Encyclopedia
An engine control unit is a type of electronic control unit
that determines the amount of fuel, ignition timing and other parameters an internal combustion engine
needs to keep running. It does this by reading values from multidimensional performance maps called Look-up tables, using input values such as engine speed and air/fuel ratio calculated from signals coming from sensor
s monitoring the engine. Before ECU's, air/fuel mixture, ignition timing, and idle speed were mechanically set and dynamically controlled by mechanical
and pneumatic
means. One of the earliest attempts to use such a unitized and automated device to manage multiple engine control functions simultaneously was the "Kommandogerät" created by BMW
in 1939, for their 801
14-cylinder aviation radial engine
.
Mixture control on computer controlled carburetors works similarly but with a mixture control solenoid or stepper motor incorporated in the float bowl of the carburetor.
) to provide better power and economy. If the ECU detects knock
, a condition which is potentially destructive to engines, and "judges" it to be the result of the ignition timing being too early in the compression stroke, it will delay (retard) the timing of the spark to prevent this.
A second, more common source of knock/ping is operating the engine in too low of an RPM range for the "work" requirement of the moment. In this case the knock/ping results from the piston not being able to move downward as fast as the flame front is expanding, but this latter mostly applies only to manual transmission equipped vehicles. The ECU controlling an automatic transmission would simply downshift the
transmission if this were the cause of knock/ping.
control built into the ECU. The engine RPM is monitored by the crankshaft position sensor
which plays a primary role in the engine timing functions for fuel injection, spark events, and valve timing. Idle speed is controlled by a programmable throttle stop or an idle air bypass control stepper motor. Early carburetor-based systems used a programmable throttle stop using a bidirectional DC motor
. Early TBI systems used an idle air control stepper motor
. Effective idle speed control must anticipate the engine load at idle. Changes in this idle load may come from HVAC systems, power steering systems, power brake systems, and electrical charging and supply systems. Engine temperature and transmission status, and lift and duration of camshaft
also may change the engine load and/or the idle speed value desired.
A full authority throttle control system may be used to control idle speed, provide cruise control functions and top speed limitation.
. In such an engine, the ECU controls the time in the engine cycle at which the valves open. The valves are usually opened sooner at higher speed than at lower speed. This can optimize the flow of air into the cylinder, increasing power and economy.
The first production engine of this type was invented ( in 2002) and introduced (in 2009) by Italian automaker Fiat
in the Alfa Romeo
MiTo. Their Multiair
engines use electronic valve control which drastically improve torque and horsepower, while reducing fuel consumption as much as 15%. Basically, the valves are opened by hydraulic pumps, which are operated by the ECU. The valves can open several times per intake stroke, based on engine load. The ECU then decides how much fuel should be injected to optimize combustion.
For instance, when driving at a steady speed, the valve will open and a bit of fuel will be injected, the valve then closes. But, when you suddenly stamp on the throttle, the valve will open again in that same intake stroke and much more fuel will be injected so that you start to accelerate immediately. The ECU then calculates engine load at that exact RPM and decides how to open the valve: early, or late, wide open, or just half open. The optimal opening and timing are always reached and combustion is as precise as possible. This, of course, is impossible with a normal camshaft, which opens the valve for the whole intake period, and always to full lift.
Programmable ECUs are required where significant aftermarket modifications have been made to a vehicle's engine. Examples include adding or changing of a turbocharger
, adding or changing of an intercooler
, changing of the exhaust system
, and conversion to run on alternative fuel
. As a consequence of these changes, the old ECU may not provide appropriate control for the new configuration. In these situations, a programmable ECU can be wired in. These can be programmed/mapped with a laptop
connected using a serial or USB cable, while the engine is running.
The programmable ECU may control the amount of fuel to be injected
into each cylinder. This varies depending on the engine's RPM and the position of the accelerator pedal (or the manifold air pressure
). The engine tuner can adjust this by bringing up a spreadsheet
-like page on the laptop where each cell represents an intersection between a specific RPM value and an accelerator pedal position (or the throttle position
, as it is called). In this cell a number corresponding to the amount of fuel to be injected is entered. This spreadsheet is often referred to as a fuel table or fuel map
.
By modifying these values while monitoring the exhausts using a wide band lambda probe to see if the engine runs rich or lean, the tuner can find the optimal amount of fuel to inject to the engine at every different combination of RPM and throttle position. This process is often carried out at a dynamometer
, giving the tuner a controlled environment to work in. An engine dynamometer gives a more precise calibration for racing applications. Tuners often utilize a chassis dynamometer for street and other high performance applications.
Other parameters that are often mappable are:
Some of the more advanced race ECUs include functionality such as launch control
, limiting the power of the engine in first gear to avoid burnouts. Other examples of advanced functions are:
A race ECU is often equipped with a data logger recording all sensors for later analysis using special software in a PC. This can be useful to track down engine stalls, misfires or other undesired behaviors during a race by downloading the log data and looking for anomalies after the event. The data logger usually has a capacity between 0.5 and 16 megabytes.
In order to communicate with the driver, a race ECU can often be connected to a "data stack", which is a simple dash board presenting the driver with the current RPM, speed and other basic engine data. These race stacks, which are almost always digital, talk to the ECU using one of several proprietary protocols running over RS232 or CANbus, connecting to the DLC connector (Data Link Connector) usually located on the underside of the dash, inline with the steering wheel
digital
/analog
designs were popular in the mid 1980s. This used analog techniques to measure and process input parameters from the engine, then used a look-up table stored in a digital ROM
chip to yield precomputed output values. Later systems compute these outputs dynamically. The ROM type of system is amenable to tuning
if one knows the system well. The disadvantage of such systems is that the precomputed values are only optimal for an idealised, new engine. As the engine wears, the system is less able to compensate than a CPU based system.
which can process the inputs from the engine sensors in real time
. An electronic control unit contains the hardware and software (firmware
). The hardware consists of electronic components on a printed circuit board
(PCB), ceramic substrate or a thin laminate substrate. The main component on this circuit board is a microcontroller chip
(CPU). The software is stored in the microcontroller or other chips on the PCB, typically in EPROM
s or flash memory
so the CPU can be re-programmed by uploading updated code or replacing chips. This is also referred to as an (electronic) Engine Management System (EMS).
Sophisticated engine management systems receive inputs from other sources, and control other parts of the engine; for instance, some variable valve timing
systems are electronically controlled, and turbocharger
wastegates can also be managed. They also may communicate with transmission control units
or directly interface electronically-controlled automatic transmission
s, traction control system
s, and the like. The Controller Area Network
or CAN bus automotive network is often used to achieve communication between these devices.
Modern ECUs sometimes include features such as cruise control
, transmission control, anti-skid brake control, and anti-theft control, etc.
General Motors' first ECUs had a small application of hybrid digital ECUs as a pilot program in 1979, but by 1980, all active programs were using microprocessor based systems. Due to the large ramp up of volume of ECUs that were produced to meet the US Clean Air Act requirements for 1981, only one ECU model could be built for the 1981 model year.http://history.gmheritagecenter.com/wiki/index.php/GM_Emission_Control_Project_Center_-_I_Was_There GM Emission Control Project Center - I Was There - GMnext] The high volume ECU that was installed in GM vehicles from the first high volume year, 1981, onward was a modern microprocessor based system. GM moved rapidly to replace carburetor based systems to fuel injection type systems starting in 1980/1981 Cadillac engines, following in 1982 with the Pontiac 2.5L "GM Iron Duke engine
" and the Corvette Chevrolet L83 "Cross-Fire" engine. In just a few years all GM carburetor based engines had been replaced by throttle body injection (TBI) or intake manifold injection systems of various types. In 1988 Delco Electronics, Subsidiary of GM Hughes Electronics, produced more than 28,000 ECUs per day, the world's largest producer of on-board digital control computers at the time.Delco Electronics Electron Magazine, The Atwood Legacy, Spring '89, page 25
s" (Full Authority Digital Engine Controls). This kind of electronic control is less common in piston-engined aeroplanes
than in automobiles, because of the large costs of certifying parts for aviation use, relatively small demand, and the consequent stagnation of technological innovation in this market. Also, a carbureted
engine with magneto
ignition and a gravity feed fuel system does not require electrical power generated by an alternator
to run, which is considered a safety advantage.
Electronic control unit
In automotive electronics, electronic control unit is a generic term for any embedded system that controls one or more of the electrical systems or subsystems in a motor vehicle....
that determines the amount of fuel, ignition timing and other parameters an internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
needs to keep running. It does this by reading values from multidimensional performance maps called Look-up tables, using input values such as engine speed and air/fuel ratio calculated from signals coming from sensor
Sensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...
s monitoring the engine. Before ECU's, air/fuel mixture, ignition timing, and idle speed were mechanically set and dynamically controlled by mechanical
Machine
A machine manages power to accomplish a task, examples include, a mechanical system, a computing system, an electronic system, and a molecular machine. In common usage, the meaning is that of a device having parts that perform or assist in performing any type of work...
and pneumatic
Pneumatics
Pneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...
means. One of the earliest attempts to use such a unitized and automated device to manage multiple engine control functions simultaneously was the "Kommandogerät" created by BMW
BMW
Bayerische Motoren Werke AG is a German automobile, motorcycle and engine manufacturing company founded in 1916. It also owns and produces the Mini marque, and is the parent company of Rolls-Royce Motor Cars. BMW produces motorcycles under BMW Motorrad and Husqvarna brands...
in 1939, for their 801
BMW 801
The BMW 801 was a powerful German air-cooled radial aircraft engine built by BMW and used in a number of German military aircraft of World War II. The engine's cylinders were in two rows of seven cylinders each, the bore and stroke were both 156 mm , giving a total capacity of 41.8 litres...
14-cylinder aviation radial engine
Radial engine
The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders point outward from a central crankshaft like the spokes on a wheel...
.
Control of fuel mixture
For an engine with fuel injection, an engine control unit (ECU) will determine the quantity of fuel to inject based on a number of parameters. If the throttle pedal is pressed further down, this will open the throttle body and allow more air to be pulled into the engine. The ECU will inject more fuel according to how much air is passing into the engine. If the engine has not warmed up yet, more fuel will be injected (causing the engine to run slightly 'rich' until the engine warms up).Mixture control on computer controlled carburetors works similarly but with a mixture control solenoid or stepper motor incorporated in the float bowl of the carburetor.
Control of ignition timing
A spark ignition engine requires a spark to initiate combustion in the combustion chamber. An ECU can adjust the exact timing of the spark (called ignition timingIgnition timing
Ignition timing, in a spark ignition internal combustion engine , is the process of setting the angle relative to piston position and crankshaft angular velocity that a spark will occur in the combustion chamber near the end of the compression stroke...
) to provide better power and economy. If the ECU detects knock
Engine knocking
Knocking in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.The...
, a condition which is potentially destructive to engines, and "judges" it to be the result of the ignition timing being too early in the compression stroke, it will delay (retard) the timing of the spark to prevent this.
A second, more common source of knock/ping is operating the engine in too low of an RPM range for the "work" requirement of the moment. In this case the knock/ping results from the piston not being able to move downward as fast as the flame front is expanding, but this latter mostly applies only to manual transmission equipped vehicles. The ECU controlling an automatic transmission would simply downshift the
transmission if this were the cause of knock/ping.
Control of idle speed
Most engine systems have idle speedIdle speed
Idle speed is the rotational speed the engine runs on when the engine is uncoupled to the drivetrain and the throttle pedal isn't depressed of a combustion engine...
control built into the ECU. The engine RPM is monitored by the crankshaft position sensor
Crankshaft position sensor
A crank position sensor is an electronic device used in an internal combustion engine to monitor the position or rotational speed of the crankshaft. This information is used by engine management systems to control ignition system timing and other engine parameters...
which plays a primary role in the engine timing functions for fuel injection, spark events, and valve timing. Idle speed is controlled by a programmable throttle stop or an idle air bypass control stepper motor. Early carburetor-based systems used a programmable throttle stop using a bidirectional DC motor
DC motor
A DC motor is an electric motor that runs on direct current electricity.-Brush:The brushed DC electric motor generates torque directly from DC power supplied to the motor by using internal commutation, stationary magnets , and rotating electrical magnets.Like all electric motors or generators,...
. Early TBI systems used an idle air control stepper motor
Stepper motor
A stepper motor is a brushless, electric motor that can divide a full rotation into a large number of steps. The motor's position can be controlled precisely without any feedback mechanism , as long as the motor is carefully sized to the application...
. Effective idle speed control must anticipate the engine load at idle. Changes in this idle load may come from HVAC systems, power steering systems, power brake systems, and electrical charging and supply systems. Engine temperature and transmission status, and lift and duration of camshaft
Camshaft
A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...
also may change the engine load and/or the idle speed value desired.
A full authority throttle control system may be used to control idle speed, provide cruise control functions and top speed limitation.
Control of variable valve timing
Some engines have Variable Valve TimingVariable valve timing
In internal combustion engines, variable valve timing , also known as Variable valve actuation , is a generalized term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine...
. In such an engine, the ECU controls the time in the engine cycle at which the valves open. The valves are usually opened sooner at higher speed than at lower speed. This can optimize the flow of air into the cylinder, increasing power and economy.
Electronic valve control
Experimental engines have been made and tested that have no camshaft, but have full electronic control of the intake and exhaust valve opening, valve closing and area of the valve opening. Such engines can be started and run without a starter motor for certain multi-cylinder engines equipped with precision timed electronic ignition and fuel injection. Such a static-start engine would provide the efficiency and pollution-reduction improvements of a mild hybrid-electric drive, but without the expense and complexity of an oversized starter motor.The first production engine of this type was invented ( in 2002) and introduced (in 2009) by Italian automaker Fiat
Fiat
FIAT, an acronym for Fabbrica Italiana Automobili Torino , is an Italian automobile manufacturer, engine manufacturer, financial, and industrial group based in Turin in the Italian region of Piedmont. Fiat was founded in 1899 by a group of investors including Giovanni Agnelli...
in the Alfa Romeo
Alfa Romeo
Alfa Romeo Automobiles S.p.A. is an Italian manufacturer of cars. Founded as A.L.F.A. on June 24, 1910, in Milan, the company has been involved in car racing since 1911, and has a reputation for building expensive sports cars...
MiTo. Their Multiair
Multiair
Multiair is an electro-hydraulic variable valve actuation technology controlling air intake in petrol or diesel engines . It is compatible with both naturally aspirated and forced-induction engines....
engines use electronic valve control which drastically improve torque and horsepower, while reducing fuel consumption as much as 15%. Basically, the valves are opened by hydraulic pumps, which are operated by the ECU. The valves can open several times per intake stroke, based on engine load. The ECU then decides how much fuel should be injected to optimize combustion.
For instance, when driving at a steady speed, the valve will open and a bit of fuel will be injected, the valve then closes. But, when you suddenly stamp on the throttle, the valve will open again in that same intake stroke and much more fuel will be injected so that you start to accelerate immediately. The ECU then calculates engine load at that exact RPM and decides how to open the valve: early, or late, wide open, or just half open. The optimal opening and timing are always reached and combustion is as precise as possible. This, of course, is impossible with a normal camshaft, which opens the valve for the whole intake period, and always to full lift.
Programmable ECUs
A special category of ECUs are those which are programmable. These units do not have a fixed behaviour and can be reprogrammed by the user.Programmable ECUs are required where significant aftermarket modifications have been made to a vehicle's engine. Examples include adding or changing of a turbocharger
Turbocharger
A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...
, adding or changing of an intercooler
Intercooler
An intercooler , or charge air cooler, is an air-to-air or air-to-liquid heat exchange device used on turbocharged and supercharged internal combustion engines to improve their volumetric efficiency by increasing intake air charge density through nearly isobaric cooling, which removes...
, changing of the exhaust system
Exhaust system
An exhaust system is usually tubing used to guide reaction exhaust gases away from a controlled combustion inside an engine or stove. The entire system conveys burnt gases from the engine and includes one or more exhaust pipes...
, and conversion to run on alternative fuel
Alternative fuel
Alternative fuels, known as non-conventional or advanced fuels, are any materials or substances that can be used as fuels, other than conventional fuels...
. As a consequence of these changes, the old ECU may not provide appropriate control for the new configuration. In these situations, a programmable ECU can be wired in. These can be programmed/mapped with a laptop
Laptop
A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device and speakers into a single unit...
connected using a serial or USB cable, while the engine is running.
The programmable ECU may control the amount of fuel to be injected
Fuel injection
Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s....
into each cylinder. This varies depending on the engine's RPM and the position of the accelerator pedal (or the manifold air pressure
MAP sensor
The manifold absolute pressure sensor is one of the sensors used in an internal combustion engine's electronic control system. Engines that use a MAP sensor are typically fuel injected. The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine's...
). The engine tuner can adjust this by bringing up a spreadsheet
Spreadsheet
A spreadsheet is a computer application that simulates a paper accounting worksheet. It displays multiple cells usually in a two-dimensional matrix or grid consisting of rows and columns. Each cell contains alphanumeric text, numeric values or formulas...
-like page on the laptop where each cell represents an intersection between a specific RPM value and an accelerator pedal position (or the throttle position
Throttle position sensor
A throttle position sensor is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the throttle valve butterfly....
, as it is called). In this cell a number corresponding to the amount of fuel to be injected is entered. This spreadsheet is often referred to as a fuel table or fuel map
Map (higher-order function)
In many programming languages, map is the name of a higher-order function that applies a given function to each element of a list, returning a list of results. They are examples of both catamorphisms and anamorphisms...
.
By modifying these values while monitoring the exhausts using a wide band lambda probe to see if the engine runs rich or lean, the tuner can find the optimal amount of fuel to inject to the engine at every different combination of RPM and throttle position. This process is often carried out at a dynamometer
Dynamometer
A dynamometer or "dyno" for short, is a device for measuring force, moment of force , or power. For example, the power produced by an engine, motor or other rotating prime mover can be calculated by simultaneously measuring torque and rotational speed .A dynamometer can also be used to determine...
, giving the tuner a controlled environment to work in. An engine dynamometer gives a more precise calibration for racing applications. Tuners often utilize a chassis dynamometer for street and other high performance applications.
Other parameters that are often mappable are:
- Ignition: Defines when the spark plugSpark plugA spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed fuels such as aerosol, gasoline, ethanol, and liquefied petroleum gas by means of an electric spark.Spark plugs have an insulated central electrode which is connected by...
should fire for a cylinder. - Rev. limit: Defines the maximum RPMRevolutions per minuteRevolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...
that the engine is allowed to reach. After this fuel and/or ignition is cut. Some vehicles have a "soft" cut-off before the "hard" cut-off. - Water temperature correction: Allows for additional fuel to be added when the engine is cold (choke) or dangerously hot.
- Transient fueling: Tells the ECU to add a specific amount of fuel when throttleThrottleA throttle is the mechanism by which the flow of a fluid is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases , but usually decreased. The term throttle has come to refer, informally and incorrectly, to any mechanism by which...
is applied. The term is "acceleration enrichment" - Low fuel pressure modifier: Tells the ECU to increase the injector fire time to compensate for a loss of fuel pressure.
- Closed loop lambda: Lets the ECU monitor a permanently installed lambda probeOxygen sensorAn oxygen sensor, or lambda sensor, is an electronic device that measures the proportion of oxygen in the gas or liquid being analyzed. It was developed by the Robert Bosch GmbH company during the late 1960s under the supervision of Dr. Günter Bauman...
and modify the fueling to achieve stoichiometric (ideal) combustion. On traditional petrol powered vehicles this air:fuel ratio is 14.7:1.
Some of the more advanced race ECUs include functionality such as launch control
Launch control (automotive)
Launch control typically refers to an electronic aid which is used to assist the drivers of various motorsports at the start of a race.Launch control also refers to an electronic setting on many modern sporting saloons and coupes which help the driver accelerate from a standing start, to gain the...
, limiting the power of the engine in first gear to avoid burnouts. Other examples of advanced functions are:
- Wastegate control: Sets up the behavior of a turbochargerTurbochargerA turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...
's wastegateWastegateA wastegate is a valve that diverts exhaust gases away from the turbine wheel in a turbocharged engine system. Diversion of exhaust gases regulates the turbine speed, which in turn regulates the rotating speed of the compressor. The primary function of the wastegate is to regulate the maximum boost...
, controlling boost. - Staged injection: Sets up the behavior of double injectors per cylinder, used to get a finer fuel injection control and atomization over a wide RPM range.
- Variable cam timingVariable Cam TimingVariable Camshaft Timing is an automobile variable valve timing technology developed by Ford. It uses electronically controlled hydraulic valves that direct high pressure engine oil into the camshaft phaser cavity. These oil control solenoids are bolted into the cylinder heads towards the front of...
: Tells the ECU how to control variable intake and exhaust cams. - Gear control: Tells the ECU to cut ignition during (sequential gearboxSemi-automatic transmissionA semi-automatic transmission is an automobile transmission that does not change gears automatically, but rather facilitates manual gear changes by dispensing with the need to press...
) upshifts or blip the throttle during downshifts.
A race ECU is often equipped with a data logger recording all sensors for later analysis using special software in a PC. This can be useful to track down engine stalls, misfires or other undesired behaviors during a race by downloading the log data and looking for anomalies after the event. The data logger usually has a capacity between 0.5 and 16 megabytes.
In order to communicate with the driver, a race ECU can often be connected to a "data stack", which is a simple dash board presenting the driver with the current RPM, speed and other basic engine data. These race stacks, which are almost always digital, talk to the ECU using one of several proprietary protocols running over RS232 or CANbus, connecting to the DLC connector (Data Link Connector) usually located on the underside of the dash, inline with the steering wheel
Hybrid digital designs
HybridHybrid computer
Hybrid computers are computers that exhibit features of analog computers and digital computers. The digital component normally serves as the controller and provides logical operations, while the analog component normally serves as a solver of differential equations.In general, analog computers are...
digital
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
/analog
Analog computer
An analog computer is a form of computer that uses the continuously-changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved...
designs were popular in the mid 1980s. This used analog techniques to measure and process input parameters from the engine, then used a look-up table stored in a digital ROM
Read-only memory
Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...
chip to yield precomputed output values. Later systems compute these outputs dynamically. The ROM type of system is amenable to tuning
Engine tuning
Engine tuning is the adjustment, modification or design of internal combustion engines to yield optimal performance, to increase an engine's power output, economy, or durability....
if one knows the system well. The disadvantage of such systems is that the precomputed values are only optimal for an idealised, new engine. As the engine wears, the system is less able to compensate than a CPU based system.
Modern ECUs
Modern ECUs use a microprocessorMicroprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
which can process the inputs from the engine sensors in real time
Real-time computing
In computer science, real-time computing , or reactive computing, is the study of hardware and software systems that are subject to a "real-time constraint"— e.g. operational deadlines from event to system response. Real-time programs must guarantee response within strict time constraints...
. An electronic control unit contains the hardware and software (firmware
Firmware
In electronic systems and computing, firmware is a term often used to denote the fixed, usually rather small, programs and/or data structures that internally control various electronic devices...
). The hardware consists of electronic components on a printed circuit board
Printed circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
(PCB), ceramic substrate or a thin laminate substrate. The main component on this circuit board is a microcontroller chip
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
(CPU). The software is stored in the microcontroller or other chips on the PCB, typically in EPROM
EPROM
An EPROM , or erasable programmable read only memory, is a type of memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile. It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages...
s or flash memory
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
so the CPU can be re-programmed by uploading updated code or replacing chips. This is also referred to as an (electronic) Engine Management System (EMS).
Sophisticated engine management systems receive inputs from other sources, and control other parts of the engine; for instance, some variable valve timing
Variable valve timing
In internal combustion engines, variable valve timing , also known as Variable valve actuation , is a generalized term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine...
systems are electronically controlled, and turbocharger
Turbocharger
A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...
wastegates can also be managed. They also may communicate with transmission control units
Transmission Control Unit
A transmission control unit or TCU is a device that controls modern electronic automatic transmissions. A TCU generally uses sensors from the vehicle as well as data provided by the Engine Control Unit to calculate how and when to change gears in the vehicle for optimum performance, fuel economy...
or directly interface electronically-controlled automatic transmission
Automatic transmission
An automatic transmission is one type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually...
s, traction control system
Traction control system
A traction control system , also known as anti-slip regulation , is typically a secondary function of the anti-lock braking system on production motor vehicles, designed to prevent loss of traction of driven road wheels...
s, and the like. The Controller Area Network
Controller Area Network
Controller–area network is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer....
or CAN bus automotive network is often used to achieve communication between these devices.
Modern ECUs sometimes include features such as cruise control
Cruise control
Cruise control is a system that automatically controls the speed of a motor vehicle. The system takes over the throttle of the car to maintain a steady speed as set by the driver.-History:...
, transmission control, anti-skid brake control, and anti-theft control, etc.
General Motors' first ECUs had a small application of hybrid digital ECUs as a pilot program in 1979, but by 1980, all active programs were using microprocessor based systems. Due to the large ramp up of volume of ECUs that were produced to meet the US Clean Air Act requirements for 1981, only one ECU model could be built for the 1981 model year.http://history.gmheritagecenter.com/wiki/index.php/GM_Emission_Control_Project_Center_-_I_Was_There GM Emission Control Project Center - I Was There - GMnext] The high volume ECU that was installed in GM vehicles from the first high volume year, 1981, onward was a modern microprocessor based system. GM moved rapidly to replace carburetor based systems to fuel injection type systems starting in 1980/1981 Cadillac engines, following in 1982 with the Pontiac 2.5L "GM Iron Duke engine
GM Iron Duke engine
Iron Dukes were fitted with fuel injection in 1982. This version was christened the Tech IV, though Car and Driver later ridiculed it as the low-Tech IV. Power output remained at ....
" and the Corvette Chevrolet L83 "Cross-Fire" engine. In just a few years all GM carburetor based engines had been replaced by throttle body injection (TBI) or intake manifold injection systems of various types. In 1988 Delco Electronics, Subsidiary of GM Hughes Electronics, produced more than 28,000 ECUs per day, the world's largest producer of on-board digital control computers at the time.Delco Electronics Electron Magazine, The Atwood Legacy, Spring '89, page 25
Other applications
Such systems are used for many internal combustion engines in other applications. In aeronautical applications, the systems are known as "FADECFADEC
Full Authority Digital Engine Control is a system consisting of a digital computer, called an electronic engine controller or engine control unit , and its related accessories that control all aspects of aircraft engine performance...
s" (Full Authority Digital Engine Controls). This kind of electronic control is less common in piston-engined aeroplanes
Fixed-wing aircraft
A fixed-wing aircraft is an aircraft capable of flight using wings that generate lift due to the vehicle's forward airspeed. Fixed-wing aircraft are distinct from rotary-wing aircraft in which wings rotate about a fixed mast and ornithopters in which lift is generated by flapping wings.A powered...
than in automobiles, because of the large costs of certifying parts for aviation use, relatively small demand, and the consequent stagnation of technological innovation in this market. Also, a carbureted
Carburetor
A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....
engine with magneto
Magneto (electrical)
A magneto is an electrical generator that uses permanent magnets to produce alternating current.Magnetos adapted to produce pulses of high voltage are used in the ignition systems of some gasoline-powered internal combustion engines to provide power to the spark plugs...
ignition and a gravity feed fuel system does not require electrical power generated by an alternator
Alternator
An alternator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current.Most alternators use a rotating magnetic field but linear alternators are occasionally used...
to run, which is considered a safety advantage.
See also
- Air flow meterAir flow meterAn air flow meter, is a device that measures how much air is flowing through a tube. It does not measure the volume of the air passing through the tube, it measures the actual speed of the air flowing through the device in a defined time segment. Thus air flow meters are simply an application of...
- Air-fuel ratio meterAir-fuel ratio meterAn air–fuel ratio meter monitors the air–fuel ratio of an internal combustion engine. Also called air–fuel ratio gauge, air–fuel meter, or air–fuel gauge...
- Automobile self starterAutomobile self starterA starter motor is an electric motor for rotating an internal-combustion engine so as to initiate the engine's operation under its own power.- History :...
- Crankshaft position sensorCrankshaft position sensorA crank position sensor is an electronic device used in an internal combustion engine to monitor the position or rotational speed of the crankshaft. This information is used by engine management systems to control ignition system timing and other engine parameters...
- Electronic control unitElectronic control unitIn automotive electronics, electronic control unit is a generic term for any embedded system that controls one or more of the electrical systems or subsystems in a motor vehicle....
(ECU), a generic term for any embedded system—not to be confused with engine control unit also abbreviated, ECU - Engine knockingEngine knockingKnocking in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.The...
- Fuel injectionFuel injectionFuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s....
- Malfunction indicator lamp (MIL)
- MotronicMotronicMotronic is the trade name given to a range of digital engine-management systems developed by Robert Bosch GmbH, commonly known as Bosch.-Motronic ML1.x:Motronic ML1.x was one of the first digital engine-management systems developed by Bosch...
- On-board diagnosticsOn-board diagnosticsOn-Board Diagnostics, or OBD, in an automotive context, is a generic term referring to a vehicle's self-diagnostic and reporting capability. OBD systems give the vehicle owner or a repair technician access to state of health information for various vehicle sub-systems...
(OBD) - Powertrain control modulePowertrain Control ModuleA Powertrain Control Module, abbreviated PCM, is an automotive component, an electronic control unit , used on motor vehicles. It is generally a combined control unit, consisting of the engine control unit and the transmission control unit. It commonly controls more than 5 factors in the car or...
(PCM) - Throttle position sensorThrottle position sensorA throttle position sensor is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the throttle valve butterfly....
- TrionicTrionicTrionic is an engine management system developed by Saab Automobile, consisting of an engine control unit that controls 3 engine aspects:# Ignition timing,# Fuel injection# Acts as a boost controller.Hence the numerical prefix 'Tri' in Trionic...
- Timing retard eliminator (TRE)
Open source engine management systems
- Open5xxxECU
- FreeEMS
- CarDAQ-plus J2534 pass-thru hardware device
Modifiable but restricted engine management systems
- MegaSquirtMegaSquirtMegaSquirt is the registered trademark of an aftermarket electronic fuel injection controller designed to be used with a wide range of spark-ignition internal combustion engines It is a complete standalone fuel injection controller with software and hardware, developed by Bruce Bowling and Al...
- ACCEL-DFI Engine Management Unit
Earliest commercial engine management system for the aftermarket
- Electromotive introduced the Total Engine Control 1 (TEC-I) in 1987, it included 60-2 (58 tooth) crank triggered distributor-less ignition. This ignition circuit was first introduced in their HPV-1 ignition in 1984. To note, the TEC-I was used as original equipment on the Vector_W8