The control unit receives information from the
different sensors and probes, analyzes it according to its program and governs
the different ignition and injection components. It can be named as: ECC, ECM,
ECU, ECCS, CPU, etc.
The ECU uses microprocessors to gather
information, process it and send signals to the excited transistors to activate
the different actuator circuits. The three main processors are RAM (temporary
memory), ROM (basic computer program) and PROM (fine tuning program), these
three microprocessors are the heart of the CPU.
Electronic Control Module
The electronic control module, or ECM, is the
brain of the fuel injection system and is divided into the following memories:
the ROM; the RAM and in some types the PROM.
ROM
or
read-only memory, is the section of the ECM that contains the main set of
instructions that the computer follows. This is the section that says, “When I
see this happening, I have to make it happen.” The microprocessor that contains
these ROM instructions is a non-volatile chip. This means that the program
designed in it cannot be deleted when power is turned off.
RAM
or random access memory, is the section that
has three main functions in the ECM. The first function acts as the ECM's
notebook; Whenever a mathematical calculation needs to be done, the ECM uses
the RAM. The second function is to store information in the block learning
multiplier (BLM) system when the engine is off or operating in open loop. The
third function is to store diagnostic codes when a system fault has been
detected. These codes are stored for fifty engine restarts or until battery
power is removed from the ECM. Unlike ROM and PROM, RAM chips are volatile
memories.
The PROM
or programmable read-only memory, is the
calibration section of the chip in the ECM. The PROM works in conjunction with
the ROM to fine-tune the fuel control and ignition timing functions for the
specific application. The PROM is also a non-volatile memory. It contains the
information about engine size, transmission type, car size and weight, rolling
resistance, drag coefficient and final drive ratio.
The ECU performs the following functions:
I/O GATE
I/O gate is the abbreviation of input-output
gate in which the microprocessor converts signals from various sensors into
codes, and also converts the operating results into signals for the operation
of the injector, power transistors, etc.
MEMORY ROM
read/exclusive memory and RAM (random access
memory) are the memories of the microcomputer. The ROM stores the ideal data
for fuel enrichment, ignition tuning, etc., and the computer can only read
these Data Memory The RAM allows the calculation results of various data sent
from the sensors to be temporarily stored. Previously stored data can be
deleted from this memory.
CPU
(central processing unit) is the brain of the
total microcomputer system and controls the various functions of the computer.
It processes the signals sent from the I/O gate while controlling the ROM and
RAM, and also transmits the computed results from the I/O gate to the injector,
power transistor and so on.
What is a digital control?
Another characteristic of the computer is that
its control unit corresponds to a digital control system. The resistance of the
cooling temperature sensor varies constantly with temperature, and this type of
signal is called “analog.” In addition to this signal, the ECU uses analog
signals from the air flow meter and others.
Meanwhile, the signal from the crankshaft
rotation angle sensor, for example, is not continuous, it is discontinuous and
is called a digital signal. Generally speaking, the digital signal represents
discontinuous values from one point to another, and its precision is lower than
that of the analog signal. However, precision can be increased by reducing the
separation between sampling points.
- The main reasons for adopting digital control system are as follows:
- The control unit can control a complicated system.
- The control unit can be made compact.
Since the signal is composed of ON-OFF pulses, the ECU operation can be limited to 0.1 operation and its combinations; This leads to reduced computing errors and good durability. In the case of analog type, the electrical noise and different characteristics of semi-conductor itself, for example, the internal resistance of the transistor, is different between the same models which can easily cause error.
In order to change the analog signal to
digital, the control unit uses the AD (analog – digital) converter.
ECU FUNCTIONS
The ECU is capable of controlling various functions.
It is also capable of providing more precise and sophisticated control. The
functions that can be controlled by the ECU are the following:
Fuel injection control
This control is basically identical to that of
the E.F.I system. however the ECU provides more detailed control. For example,
a learning control system is used to maintain an optimal idle mixture ratio at
all times.
Ignition tuning control
It corresponds to a new function. The optimal
ignition setting is determined by receiving signals from different sensors.
Fuel pump control.
The ECU controls the voltage applied to the
fuel pump and reduces the voltage applied to the fuel pump to reduce fuel pump
noise and electrical power consumption at idle.
Auto diagnosis
Check whether the input and output signal
systems to and from the control unit are normal.
Idle speed control
It receives signals from various sensors and
regulates the engine to optimal idle speed according to the engine load.
Idle Control.
Increases idle speed when battery voltage is
low, or when many charge switches are activated.
Pressure regulator control
Temporarily increases fuel pressure when the engine is started with high coolant temperature. There is another module in addition to the control unit.
Air regulator control.
In the conventional system the air regulator
was normally activated with the ignition switch in the ON position. In other
cases, the air regulator is activated only when the fuel pump is operating, in
order to reduce electrical energy consumption.
Others.
E.G.R. control is also used. (exhaust gas
recirculation), A.V.I. control. (air indicator valve), etc.
conclusion
From the point of view of the function it
performs, a microprocessor is responsible for executing the instructions of a
program one at a time. A ROM (READ ONLY MEMORY) memory is an integrated circuit
that is designed to permanently store the program and data accessed by the
microprocessor. There are different types of memories that fall into this
category. They work in a way analogous to a CD or video cassette, once
something is recorded on them, even if the power is cut, the data recorded on said
medium is not erased.
Anecdotally, PROM memory manufacturers claim
that the data recorded in them remains unchanged for 20 years without any power
source connected. What's more, every time they connect to their source, the
data stored there is secured for another 20 years.
A RAM memory (RANDOM ACCESS MEMORY) is a memory
that is designed to store data temporarily. In some ways this type of memory is
similar to the short-term memory of our brain.
When the RAM stops receiving power, it loses
its contents. But an ECU also has what is called KAM memory (KEEP ALIVE
MEMORY), which is neither more nor less than a RAM memory powered directly by
the car battery (without going through the ignition key). In a KAM memory, the
fault codes that are loaded due to anomalies in the injection system are
recorded to ensure that when the car enters the workshop, data is available on
which component caused the failure.
The BUS is responsible for transmitting the
information. The function that a BUS has within the ECU is to connect one chip
to another. In the ECU, instead of using cables as connectors, copper tracks
are used as conductors in the printed circuit.