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What is an electronic control unit?

Progress in automotive technology is above all due to electronic control units. Their sophisticated electronics can now control highly complex driving functions in modern vehicles.

The ECU is the car's brain

The greatest advances in automotive engineering began in the late 1970s with the introduction of the electronic control unit (ECU). Developments in the field of microelectronics and progress in electromechanical sensors meant that mechatronics began to replace the mechanical systems that were predominant at that time. The first ECUs communicating via a controller area network (CAN) bus gradually replaced electric point-to-point connections via cables, flasher units and relays. In the meantime, miniaturised semiconductors installed in digital ECUs in the form of an embedded system perform almost all of the functions in the entire vehicle. What is more, all the relevant information in the ECUs are collected and processed.

The central processing unit (CPU) uses powerful 16-bit and 32-bit processors. Only by using these high-performance processors is it possible to collect and process all the relevant information from the sensors and ultimately to control the actuators. Generally speaking, these are electric motors or electromagnetic valves that convert signals from the ECU into an action. In the case of an engine management system, the system functions that are controlled by the ECU include:

Key elements of an electronic control unit

To ensure that the central processing unit can use the sensor signals necessary for processing, these must first of all be prepared by special input circuitry. Because the sensor signals are usually analogue, analogue-digital converters are used. These calculate digital numerical values from the input voltages to enable them to be further processed by the CPU. The programs and characteristic maps required for this – in other words links, algorithms and calibration data – are written by the car maker into a semiconductor memory even during the production process.

To avoid the need to replace the entire ECU after each model change, automotive developers nowadays use flash EEPROMs as electronic data storage devices. These special semiconductor memories (FPGA, field-programmable gate array) can be reprogrammed. This enables calibration engineers to perform changes to the ECU at short notice and to adapt them to the latest state of development. A further advantage of this strategy is that only a single piece of ECU hardware is required during the production of the vehicle. The engine and calibration variants with their individual ECU data are not written to the memory until just before the end of the assembly line.

Connected ECUs are becoming intelligent

Today, there are hardly any functions in the car that are not performed by an ECU. As a result, even vehicles in the mid-size segment have more than 70 electronic control units installed in them. This means that modern cars are highly complex, connected system in which around 80 percent of all innovations are due to the use of electronic systems. And in the meantime, 90 percent of these are determined by software functions. For that reason too, there is a growing demand for data storage space and computing time in ECUs. After all, several hundred million lines of code must be saved and processed.

Along with the trend towards connecting cars with one another (car-to-car) as well as with the infrastructure (car-to-x), there is also an increase in the complexity of the software for ECUs. Firstly, more and more safety-relevant driving functions are being controlled by this software. These include, for example, driver assistance systems (DAS) such as lane departure warning (LDW) and adaptive cruise control (ACC), which need to use cryptographic processes in order to protect them against unauthorised access. Secondly, these new vehicle functions are being intelligently connected with existing systems, thus paving the way to autonomous vehicles.

ECU development, testing and validation

This development has knock-on effects on the entire vehicle development process. For example, special tools and systems are necessary today in order to teach-in the ECUs. While the calibration of the engine management system takes place on a virtual engine, the entire vehicle dynamics are tested on the basis of a virtual vehicle. The advantage of this model-based software development (testing and validation) is that it is based on static and dynamic testing processes. During these processes, the programs are tested with regard to functionality and code generation ability.

They are also tested to ensure that they comply with design quality measures, which means that they are in accordance with documentation and modelling guidelines. In order to secure the quality of the functional models, developers apply so-called in-the-loop simulation methods which enable extreme situations to be simulated.

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Dipl.-Ing. Dietmar Bichler
Bertrandt AG

Dipl.-Ing. Kurt Blumenröder

Dr.-Ing. Joachim Damasky

Prof. Dr.-Ing. Lutz Eckstein
RWTH Aachen, WKM

Dr.-Ing. Ulrich Eichhorn
Volkswagen AG

Dr. rer. nat. Andreas Eilemann
Mahle Behr GmbH & Co. KG

Dipl.-Ing. Klaus Fröhlich

Prof. Dr.-Ing. Burkhard Göschel
Burkhard Goeschel Consultancy

Prof. Dr.-Ing. Peter Gutzmer
Schaeffler AG

Dr.-Ing. Markus Heyn
Robert Bosch GmbH

Dr.-Ing. Carsten Intra
MAN Truck & Bus AG

Prof. Dr.-Ing. Pim van der Jagt
Ford-Forschungszentrum Aachen GmbH

Dr.-Ing. Stefan Knirsch
Audi AG

Dipl.-Ing. Ralph Lauxmann
Continental Teves AG & Co. oHG

Dipl.-Ing. (BA) Joachim Mathes
Valeo Schalter und Sensoren GmbH

Dr.-Ing. Harald Naunheimer
ZF Friedrichshafen AG

Dipl.-Ing. Jörg Ohlsen
Edag GmbH & Co. KGaA

Prof. Dr. Dipl.-Ing. Peter Pfeffer
Hochschule München

Prof. Dr.-Ing. Rodolfo Schöneburg

Dipl.-Ing. (FH) Dipl.-Wirtsch.-Ing. (FH) Wolfgang Schwenk
Adam Opel AG

Dr. Michael Steiner
Dr. Ing. h.c. F. Porsche AG

Prof. Dr.-Ing. Thomas Weber
Daimler AG

Dr.-Ing. Christian Wiehen
Wabco GmbH

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