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❖What is an ECU
❖Hardware Design of an ECU
❖Operation of an ECU
What is an ECU
In the Automobile industry an electronic control unit (ECU) is an
embedded electronic device, basically a digital computer, that reads
signals coming from sensors placed at various parts and in different
components of the car and depending on this information controls
various important units e.g. engine and other automated operations
within the car among many.
ECU(Electronic Control Unit) and its mount location
Types of ECU
ECM - Engine Control Module
EBCM - Electronic Brake Control Module
PCM - Powertrain Control Module
VCM - Vehicle Control Module
BCM - Body Control Module
Components of ECU
An ECU consists of a number of functional blocks:
1. Power Supply – digital and analog (power for analog sensors)
2. MPU – microprocessor and memory (usually Flash and RAM)
3. Communications Link – (e.g. CAN bus)
4. Discrete Inputs – On/Off Switch type inputs
5. Frequency Inputs – encoder type signals (e.g. crank or vehicle speed)
6. Analog Inputs – feedback signals from sensors
7. Switch Outputs – On/Off Switch type outputs
8. PWM Outputs – variable frequency and duty cycle (e.g. injector or ignition)
9. Frequency Outputs – constant duty cycle (e.g. stepper motor – idle speed
What an ECU does
The ECU uses closed-loop control, a control scheme that monitors outputs of
a system to control the inputs to a system, managing the emissions and fuel
economy of the engine (as well as a host of other parameters).
Gathering data from dozens of different sensors, the ECU performs millions of
calculations each second, including looking up values in tables, calculating the
results of long equations to decide on the best spark timing or determining how
long the fuel injector is open.
A modern ECU might contain a 32-bit, 40-MHz processor, which
may not sound fast compared to the processors we probably have
in our PCs, but the processor in our car runs a much more efficient
code. The code in an average ECU takes up less than 1
megabyte(MB) of memory. By comparison, we probably have at
least 2 gigabytes (GB) of programs on our computers -- 2,000 times
the amount in an ECU.
The software is structured according to AUTOSAR, with application layer, RTE
and base software. The architecture is divided into four main parts:
Application Layer: Containing the application functions, primarily model
Run Time Environment (RTE): Abstraction of the ECU hardware, provid-
ing a common runtime environment
Base Software: Basic services for communication, I/O, memory and system
Flash Loader: Standalone application allowing a flash update of the system
Need of AUTOSAR
Without a proper software standard every company built its own software
solution or utilised 3rd party software for the same. Integration of 3rd party
software created implementation issues (e.g. wrapper software, interface
components), issues with testing methodology etc. with several tool chains
further required, to associate the hardware with the software.
It piled up the issues for Tier-1 manufacturers who now had to integrate
different software for each OEM.
These integration problems proved difficult to identify and costly to debug in the
AUTOSAR provides different functional blocks for the integration of application
layer with the micro-controller.
Depending upon the nature of the circuit the
Engine mappings can change completely. On
slower and twister tracks, the engine control
system will help the driver have more control on
the throttle input by making the first half of the
pedal movement very sensitive.
At high speed circuits, the driver has to jump on the
throttle more, rather than gradually applying full
throttle. The accelerator will be set so that only a
small movement will result in full engine
This function has to be repeated every 20 milliseconds.
− Read the data captured by the Analog-to-Digital Converter (ADC) on the Channel to
which the Accelerator Pedal is Connected.
− Using this data, look-up the value from a multi-dimensional Table (Map), which also
contains the Engine RPM (Rotations per Minute), as another input axis.
− Take the output value from the Map, multiply it by a correction factor (depending on, for
e.g. Performance or Economy Mode).
− The output of this calculation is the Torque to be generated by the Engine.
− Repeat this sequence every 20 milliseconds.
Some other applications
Anti Lock Braking System(ABS)
Electronics Brake Distribution Force(EBD)
Airbag Control System(ACS)
and many more.
The worse place in the world to put a sophisticated piece of electronics is under
the bonnet of a car due to massive vibrations, constant heat variations and
intense radio interference from the ignition system added to the fact that the
manufacturers must produce on a huge scale, this causes so many problems
and design flaws with modern day ECUs.