What is an Engine Control Unit?
Engine control unit is a device that maintains different features of internal combustion engines operations. Engine control unit is also known as engine control module (ECM). When engine control unit (ECU) monitors engine and transmission both the functions then its called power train control unit or module. The basic function of ECU is to check the amount of fuel injected in every cylinder in each cycle of engine.
Many recent ECUS’ manufactured in latest models of vehicles also has responsibility to check the ignition timing, variable valve timing (VVT), the level of boost maintained by turbocharger, and to control peripherals. Other than this, ECU also has responsibility to settle on amount of furl, ignition timing, and other factors by checking the engine through sensors. These include MAP sensor, throttle place sensor, air temperature sensor, oxygen sensor, etc. many engine factors were rigid before ECU’s were introduced. Carburetor or injector pump decides on amount of fuel per cylinder per engine cycle.
Control of Fuel Injection
ECU determines how much fuel should be used in engine with fuel injection. It considers limits in determining the fuel's quantity. Let’s consider the throttle pedal. If we press throttle pedal down, throttle body opens up and gives chance to more air to be pulled in engine. Then ECU will then work on adding more fuel depending on air in engine. More fuel will be brought-in in case engine is not humid yet.
Control of Ignition Timing
Spark is needed in ignition engine to start combustion in burning chamber. ECU has option of regulating the time of spark so that better control and economy is produced. If knock is detected by ECU then ECU will stoppage the spark timing to prevent knock. Knock is the destructive situation to engine in a way that causes early ignition timing in compression stroke. Using the engine in low RPM range can be another source of knock. Here knock is caused from piston whose speed of moving down is less than flame which is mounting up in front. This situation usually occurs in manual transmission equipped vehicles. If ECU is having hold of automatic transmission then it would shift the transmission downward.
Control of Variable Valve Timing
Some engines have feature of variable valve timing. It means that ECU has a control over time in the engine cycle where valves open. Valves open at less time when vehicle is in higher speed that lower speed. This boosts up the flow of air into cylinder causing increase in power and economy.
Aftermarket has an exclusive class of ECU’s. This exclusive class of ECU is programmable. What makes these ECU’s special is that their attitude is not constant but can be programmed again by user. These ECU’s are not needed in every vehicle but in those where some specific modifications have been made in engine. Like adding or changing of a turbo charger, adding or changing of an intercooler, changing of the exhaust system, and conversion to run on alternative fuel.
These are some cases where programmable ECUs can be needed. This means that these can be reprogrammed by connecting laptop to USB cable when engine is running. One more advantage of programmable ECU is that it monitors the quantity of fuel to be inserted in every cylinder. Amount of fuel to be injected differs with the RPM of an engine and position of gas pedal. This can be regulated by engine tuner which brings the spreadsheet like page on laptop where every cell embodies a connection between a definite RPM value and a gas pedal position.
Many matching to the quantity of fuel to be inserted are penetrated in this cell. By adjusting the values when scrutinizing the exhausts by using a wide band lambda probe to check if engine is running richly or leanly, the tuner can locate the optimal amount of fuel to insert to the engine at every combination of RPM and throttle position. All this procedure often takes place at dynamometer where a restricted but calm atmosphere is given to tuner to operate in.
In mid 1980s, hybrid digital/analog designs were very well-liked. Analog skills were used by this in order to computer and practice the input parameters from the engine. Next was used a look-up table stored in a digital ROM chip to surrender pre-computed output values. The ROM system is easy to tune only if one is acquainted to the system. This system also has some disadvantages. One of which is that pre-computed values are best only for novel engine.
Now technology has developed a lot and so has modern ECUs. In latest ECUs, a microprocessor is used to practice the inputs from engine sensors in right time. Hardware and software also called firm ware are contained in ECU. The hardware of an ECU comprises electronic components on a printed circuit board (PCB), ceramic substrate or a thin laminate substrate. The most important element of circuit board is microcontroller chip abbreviated as CPU. On the other hand, software is hoard in microcontroller or other chips on PCB; usually in EPROMs or flash memory where CPU can be programmed again by uploading updated code or replacing chips. This is also known as engine management system abbreviated as EMS.
Stylish engine management systems accept input from other sources and monitor other parts of engine. Like variable valve timing systems and turbocharger waste gates.
They also may communicate with transmission control units or directly interface electronically-controlled automatic transmissions, traction control systems, and the like. The Controller Area Network or CAN bus automotive network is often used to achieve communication between these devices. Some developed features are manufactured in latest ECU like cruise control, transmission control, anti skid brake control, anti theft control, etc.
Below are some components in ECU supported by processor:
Analog to digital converter is used to study the sensors in vehicle. Oxygen sensor is an example. Oxygen sensors have an output analog voltage between 0 volts to 1.1 volts. As it is clear from name “ANALOG to DIGITAL CONVERTOR”; this convertor converts the voltage value in 10 bit digital number because the system only recognize digital numbers.
High-level digital outputs
The task of ECU in latest models of vehicles is to fire the spark plug, to open and close the fuel injectors and to turn off and turn on the cooling fan. To achieve these tasks, digital output is requisite. There are only two options for digital output i.e. either on or off and no in-between. For example: output for controlling the cooling fan can supply 12 V and 0.5 amps to fan relay only when it in and 0 V when off. The digital output itself acts as a relay. Transistor in digital output is rejuvenated by output processed by quantity of strength. This permits it to provide more power to the cooling fan relay which in turn supplies a larger quantity of power to the cooling fan.
Sometimes ECU needs to supply analog voltage output in order to encourage engine gears. As the processor on ECU is a digital gadget, so a special module is required to convert the digital number into an analog voltage.
Many times inputs and outputs are needed to be fine-tuned before they are even read. For example, analog to digital convertor reads the voltage from oxygen sensor might be places in to read 0 to 5 volt signal where as oxygen sensor outputs a 0 to 1.1 V signal. Level of signal coming in or out is regulated by signal conditioner. For example, if signal conditioner is applied that would multiply the voltage coming from the oxygen sensor by four, we would get 0 to 4.4 V signals which would then permit the analog to digital convertor to read the voltage more precisely.
These communication chips realized the different communication standards used on car. There are many different standards used in cars but the most popular is CAN i.e. controller area networking. This is the communication standard that permits communication speed of 500 kilobits per second. This standard has more speed as compare to older standards. Controller area networking (CAN) bus communicates by using couple of wires.