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An engine control unit (ECU) is an electronic control unit which controls various aspects of an internal combustion engine's operation. In automotive electronics an electronic control unit (ECU also called a Control unit, or Control module, is an Embedded system that controls one or more The internal combustion engine is an engine in which the Combustion of Fuel and an Oxidizer (typically air occurs in a confined space called a The simplest ECUs control only the quantity of fuel injected into each cylinder each engine cycle. More advanced ECUs found on most modern cars also control the ignition timing, variable valve timing (VVT), the level of boost maintained by the turbocharger (in turbocharged cars), and control other peripherals. Ignition timing in an Internal combustion engine is the process of setting the time that a spark will occur in the combustion chamber (during the Power stroke) relative Variable valve timing, or VVT, is a generic term for an Automobile Piston engine technology A turbocharger, or turbo, is an air Compressor used for forced-induction of an Internal combustion engine.

ECUs determine the quantity of fuel, ignition timing and other parameters by monitoring the engine through sensors. These can include, MAP sensor, throttle position sensor, air temperature sensor, oxygen sensor and many others. The examples and descriptions in this article apply strictly to Four-stroke cycle gasoline engines A throttle position sensor (TPS is a Sensor used to monitor the position of the Throttle in an Internal combustion engine. An oxygen sensor, or lambda sensor is an electronic device that measures the proportion of Oxygen (O2 in the gas or liquid being analyzed Often this is done using a control loop (such as a PID controller). A control system is a device or set of devices to manage command direct or regulate the behavior of other devices or systems A proportional–integral–derivative controller (PID controller is a generic Control loop Feedback mechanism widely used in industrial Control systems

Before ECUs most engine parameters were fixed. The quantity of fuel per cylinder per engine cycle was determined by a carburetor or injector pump. A carburetor (North American spelling or carburettor ( Commonwealth spelling) is a device that blends air and Fuel for an Internal

Contents

ECU operation

Control of fuel injection

For an engine with fuel injection, an ECU will determine the quantity of fuel to inject based on a number of parameters. Fuel injection is a system for mixing fuel with air in an Internal combustion engine. 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).

Control of ignition timing

A spark ignition engine requires a spark to initiate combustion in the combustion chamber. The term spark-ignition engine is normally used to refer to Internal combustion engines where the fuel-air mixture is ignited with a spark. An ECU can adjust the exact timing of the spark (called ignition timing) to provide better power and economy. Ignition timing in an Internal combustion engine is the process of setting the time that a spark will occur in the combustion chamber (during the Power stroke) relative 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. Knocking (also called knock, detonation or spark knock, pinking in UK English or pinging in US English in spark-ignition

A second, more common source, cause, 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 were this the cause of knock/ping.

Control of idle speed

Most engine systems have idle speed control built into the ECU. Idle speed is the minimum operating speed (generally measured in revolutions per minute or rpm of the Crankshaft) of a Combustion Engine. 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. The crankshaft, sometimes casually abbreviated to crank, is the part of an Engine which translates reciprocating Linear 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 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 Timing. Variable valve timing, or VVT, is a generic term for an Automobile Piston engine technology In such an engine, the ECU controls the time in the engine cycle at which the valves open. The valves are usually opened later at higher speed than at lower speed. This can optimise 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 has 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 with out 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-reductiton improvements of a mild hybrid-electric drive, but without the expense and complexity of an oversized starter motor. Hybrid Vehicles make use of both an on-board Rechargeable energy storage system (RESS and a fueled power source for vehicle propulsion. [1]For more information also see the following references:

1. Freescale site: http://www.freescale.com/webapp/sps/site/application.jsp?nodeId=02Wcbf56hRCrcd

2. Utah University site: http://www.mech.utah.edu/senior_design/06/index.php/ElectronicValveControl/HomePage

3. New York Times Article 8/23/03: http://query.nytimes.com/gst/fullpage.html?res=9503E1DB1F30F932A1575BC0A9659C8B63&sec=&spon=&pagewanted=1

4. MIT Technology Review November 2002: http://grants.nih.gov/grants/funding/SBIRConf2002/arms/sld029.htm

Programmable ECUs

A special category of ECUs are those which are programmable. Technology Review is a magazine published by Technology Review Inc a media company owned by the Massachusetts Institute of Technology. These units do not have a fixed behavior, but 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, adding or changing of an intercooler, changing of the exhaust system, and conversion to run on alternative fuel. A turbocharger, or turbo, is an air Compressor used for forced-induction of an Internal combustion engine. An intercooler, or Charge air cooler, is an air-to-air or air-to-liquid heat exchange device used on turbocharged and supercharged (forced Alternative fuels, also known as non-conventional Fuels are any Materials or substances that can be used as a Fuel, 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 connected using a serial or USB cable, while the engine is running. A laptop computer, also known as a notebook computer, is a small Personal computer designed for mobile use.

The programmable ECU may control the amount of fuel to be injected into each cylinder. Fuel injection is a system for mixing fuel with air in an Internal combustion engine. This varies depending on the engine's RPM and the position of the gas pedal (or the manifold air pressure). The examples and descriptions in this article apply strictly to Four-stroke cycle gasoline engines 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 a gas pedal position (or the throttle position, as it is called). A spreadsheet is a Computer application that simulates a paper worksheet A throttle position sensor (TPS is a Sensor used to monitor the position of the Throttle in an Internal combustion engine. In this cell a number corresponding to the amount of fuel to be injected is entered.

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. An oxygen sensor, or lambda sensor is an electronic device that measures the proportion of Oxygen (O2 in the gas or liquid being analyzed This process is often carried out at a dynamometer, giving the tuner a controlled environment to work in. For the dynamometer used in railroading see Dynamometer car. A dynamometer or "dyno" for short is a machine used to measure

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. A megabyte is a unit of Information or Computer storage equal to either 106 (1000000 Bytes or 220 (1048576 bytes depending on

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, CANbus]].

ECU flashing

Many recent (around 1996 or newer) cars use OBD-II ECUs that are sometimes capable of having their programming changed through the OBD port. On-Board Diagnostics, or OBD, in an Automotive context is a generic term referring to a vehicle's self-diagnostic and reporting capability Automotive enthusiasts with modern cars take advantage of this technology when tuning their engines. Rather than use an entire new engine management system, one can use the appropriate software to adjust the factory equipped computer. By doing so, it is possible to retain all stock functions and wiring while using a custom tuned program. This should not be confused with "chip tuning", where the owner has ECU ROM physically replaced with a different one -- no hardware modification is (usually) involved with flashing ECUs, although special equipment is required.

Factory engine management systems often have similar controls as aftermarket units intended for racing, such as 3-dimensional timing and fuel control maps. They generally do not have the ability to control extra ancillary devices, such as variable valve timing if the factory vehicle was a fixed geometry camshaft or boost control if the factory car was not turbocharged. Variable valve timing, or VVT, is a generic term for an Automobile Piston engine technology Boost control is the principle of controlling the boost level produced in the Intake manifold of a turbocharged or supercharged engine by affecting

History

Hybrid digital designs

A hybrid digital design was popular in the mid 1980s. This used analogue 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. In Computer science, a lookup table is a Data structure, usually an Array or Associative array, often used to replace a runtime computation with Later systems compute these outputs dynamically. The ROM type of system is amenable to tuning if one knows the system well. Engine tuning is the adjustment modification or design of Internal combustion engines to yield optimal performance either in terms of power output or economy 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 microprocessor which can process the inputs from the engine sensors in real time. A microprocessor incorporates most or all of the functions of a Central processing unit (CPU on a single Integrated An electronic control unit contains the hardware and software (firmware). In Computing, firmware is a computer program that is Embedded in a hardware device for example a Microcontroller. The hardware consists of electronic components on a printed circuit board (PCB), ceramic substrate or a thin laminate substrate. A printed circuit board, or PCB, is used to mechanically support and electrically connect Electronic components using conductive pathways or traces 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 EPROMs or flash memory so the CPU can be re-programmed by uploading updated code or replacing chips. An EPROM, or E rasable P rogrammable '''''R'''ead-'''O'''nly '''M'''emory'', is a type of memory chip that retains its Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed 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. Variable valve timing, or VVT, is a generic term for an Automobile Piston engine technology A turbocharger, or turbo, is an air Compressor used for forced-induction of an Internal combustion engine. They also may communicate with transmission control units or directly interface electronically-controlled automatic transmissions, traction control systems, and the like. 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 An automatic transmission (commonly "AT" or "Auto" is an Automobile Gearbox that can change Gear ratios automatically as the vehicle A traction control system ( TCS) also known as Anti-Slip Regulation ( ASR) on current production Vehicles are typically (but not necessarily The Controller Area Network or CAN bus automotive network is often used to achieve communication between these devices.

Modern ECUs sometimes include features as cruise control, transmission control, anti-skid brake control, and anti-theft control, etc. Cruise control (sometimes known as speed control or autocruise) is a system that automatically controls the rate of motion of a Motor vehicle.

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[2]. 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 Small-Block engine#L83 "Cross-Fire" engine. The Iron Duke (also called the 2500, 151, Pontiac 25, Cross Flow, and Tech IV, though the decal on the air filter assemblies Introduction Chevrolet 's Small-block V8 is a famous Automobile 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[3].

Other applications

Such systems are used for many internal combustion engines in other applications. In aeronautical applications, the systems are known as "FADECs" (Full Authority Digital Engine Controls). A FADEC (Full Authority Digital Engine Control is a system consisting of a Digital Computer, called an Electronic Engine Control (EEC or Electronic Control 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. Overview Fixed-wing aircraft range from small training and recreational aircraft to Wide-body aircraft and military cargo aircraft. Also, a carburated engine with magneto ignition and a gravity feed fuel system does not require any electrical power to run, which is a safety bonus. A carburetor (North American spelling or carburettor ( Commonwealth spelling) is a device that blends air and Fuel for an Internal This article is about the Engine component For other uses of the term see Magneto (disambiguation.

ECU failures

As usually occurs with a technology shift, computer-controlled engine management has replaced old failure modes with new ones. With advanced age, a failing ECU can cause seemingly random starting and driveability faults. For example, a vehicle may refuse to start when cranked with the starter motor, but may respond easily to a push start. An automobile self-starter (commonly "starter motor" or simply "starter" is an Electric motor that initiates rotational motion in a car's Internal Failing electrolytic capacitors in the ECU no longer smooth the power supply to the microprocessor, and the varying load on the starter motor causes sufficient line voltage fluctuation that the computer reboots repeatedly while attempting to start the engine. An electrolytic capacitor is a type of Capacitor that uses an ionic conducting liquid as one of its plates An industry has evolved to refurbish ECUs with this and other types of failures related to age and use.

See also

Manufacturers of aftermarket ECUs

Open source engine management systems

Pseudo open source engine management systems

DIY engine management systems

References

  1. ^ Automotive_electrical_systems_circa_2005_-_IEEE_Spectrum. MegaSquirt is an Aftermarket Electronic fuel injection (EFI controller designed to be used with a wide range of Internal combustion engines It is IEEE. The Institute of Electrical and Electronics Engineers or IEEE (read eye-triple-e) is an international Non-profit, professional organization Retrieved on 2008-03-05. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 363 - Roman Emperor Julian moves from Antioch with an army of 90000 to attack the Sassanid Empire, in a
  2. ^ GM Emission Control Project Center - I Was There - GMnext
  3. ^ Delco Electronics Electron Magazine, The Atwood Legacy, Spring '89, page 25

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