- Engine control unit
An engine control unit "(ECU)" is an
electronic control unitwhich controls various aspects of an internal combustion engine's operation. 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 other peripherals.
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 sensorand many others. Often this monitoring and control is done using a control loop(such as a PID controller).
Before ECUs, most engine parameters were fixed. The quantity of fuel per cylinder per engine cycle was determined by a
carburetoror injector pump.
Working of ECU
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. 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. An ECU can adjust the exact timing of the spark (called
ignition timing) 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, 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 speedcontrol built into the ECU. The engine RPMis monitored by the crankshaftposition 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 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. 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. [cite web |title=Automotive_electrical_systems_circa_2005_-_IEEE_Spectrum|publisher=
IEEE|accessdate=2008-03-05|url=http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel3/6/11140/00511737.pdf?arnumber=511737] For more information also see the following references:
1. Freescale site: http://www.freescale.com/webapp/sps/site/application.jsp?nodeId=02Wcbf56hRCrcd
2. University of Utah 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
Technology ReviewNovember 2002: http://grants.nih.gov/grants/funding/SBIRConf2002/arms/sld029.htm
A special category of ECUs are those which are programmable. 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 exhaustsystem, 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 laptopconnected using a serial or USBcable, 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 gas 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 a gas 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.
By modifying these values while monitoring the exhausts using a wide band
lambda probeto 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.
Other parameters that are often mappable are:
*Ignition: Defines when the
spark plugshould fire for a cylinder.
*Rev limit: Defines the maximum RPM that the engine is allowed to rev to. After this fuel and/or ignition is cut.
*Water temperature correction: Allows for additional fuel to be added when the engine is cold (choke).
*Transient fueling: Tells the ECU to add a specific amount of fuel when
*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 probe and modify the fueling to achieve
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:
*Waste gate control: Sets up the behavior of a turbo waste gate, controlling
*Banked 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 timing: Tells the ECU how to control variable intake and exhaust cams.
*Gear control: Tells the ECU to cut ignition during (sequential gearbox) 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
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
Many recent (around 1996 or newer) cars use
OBD-IIECUs that are sometimes capable of having their programming changed through the OBD port. 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 timingif the factory vehicle was a fixed geometry camshaft or boost controlif the factory car was not turbocharged.
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 tablestored 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.
Modern ECUs use a
microprocessorwhich 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 EPROMs or flash memoryso 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 timingsystems are electronically controlled, and turbochargerwastegates can also be managed. They also may communicate with transmission control units or directly interface electronically-controlled automatic transmissions, traction controlsystems, and the like. The Controller Area Networkor 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.
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://wiki.gmnext.com/wiki/index.php?title=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] .
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). 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 carburated engine with magneto ignition and a gravity feed fuel system does not require any electrical power to run, which is a safety bonus.
As usually occurs with a technology shift, computer-controlled engine management has replaced old failure modes with new onesFact|date=September 2007. 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. 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 engineFact|date=September 2007. An industry has evolved to refurbish ECUs with this and other types of failures related to age and use.
Air flow meter
Air-fuel ratio meter
Malfunction Indicator Lamp
Automobile self starter
Powertrain Control Module
Manufacturers of aftermarket ECUs
Bowling & Grippo(Makers of MegaSquirtopen source ECU)
* [http://decselectronics.com/ DECS ] (
Low cost ECU)
DTA Competition Engine Management Systems
Electromotive TEC³r and TECgt
EMS Aftermarket Engine Management
General Engine Management Systems
Haltech Engine Management Systems
KMS( Kronenburg Management Systems)
Performance Electronics, Ltd.
Simple Digital Systems
Open source engine management systems
*CarDAQ-plus J2534 pass-thru hardware device
Pseudo open source engine management systems
DIY engine management systems
* [http://www.autoshop101.com/autoshop15.html Articles from Toyota Motor Sales, USA, Inc. at "Autoshop 101"]
* [http://allobd.com/whatisJ2534.asp Explanation of the SAE J2534-1 Standard for pass-thru programming of ECUs]
* [http://allobd.com/LabViewVIs_J2534.asp LabVIEW VIs for developing test systems with vehicle PassThru (J2534-1)]
* [http://www.adi.com/products_emu_pci.htm Interesting tool used by ECU developers to electrically emulate four-stroke engine signals]
* [http://www.diyefi.org Do It Yourself Engine Management]
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