Engine control

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Interior view of an engine control of the VW Golf III

A motor controller (also engine control unit ; English Engine Control Unit ECU) is one of an automotive developed for a particular type of engine electronics ( controller ), which takes over the control, regulation and monitoring of engine functions.

The beginnings of engine control were initially based on analog electronics (such as the Bosch D-Jetronic ). They were used to implement electronic fuel injection .

Powerful digital microprocessors or microcontrollers are used in modern engine control units . Systems with multiple CPUs are also quite common. They control the internal combustion processes in the engine and much more.

Demarcation

The term engine control is v. a. used in connection with the Otto engine . The very similar engine control for the diesel engine is dealt with under Electronic Diesel Control . Hybrid vehicles usually have a control for the combustion engine and a control for the electric machine.

Basics and structure

In current internal combustion engines , the engine control unit controls and monitors the combustion processes in the engine in such a way that the desired driving behavior is achieved and the applicable emissions standard is complied with (e.g. lambda control ). To do this, the engine control unit must calculate and output all control signals synchronously with the engine-internal process. This applies in particular to the air filling of the combustion chamber, the fuel injection and the control of the ignition point up to the regeneration / cleaning of the exhaust system. Engine control units can have over 200 connections (analog and digital I / O interfaces).

In the case of large combustion engines, several engine control units can also be used according to the master-slave principle. The significantly larger number of sensors and actuators is taken into account here (e.g. for injection and ignition systems per cylinder but also air and lambda sensors in multi-flow systems)

Typical input signals of the motor control are:

Further input signals are generated by the driver, for example:

  • Accelerator pedal angle / travel (accelerator pedal travel),
  • Clutch pedal switch,
  • Brake signal switch,
  • Vehicle speed control system ( cruise control ).

Typical output signals of the motor control are:

  • Control of the injection valves ,
  • Activation of the ignition,
  • Control of the throttle valve actuator,
  • Control of the exhaust gas recirculation valve,
  • Activation of the turbocharger (waste gate or VTG ),
  • Camshaft adjustment,
  • Fuel pump.
Diagram showing how a vehicle control unit works

Modern motor controls are implemented with microcontrollers such as the Infineon TriCore . You have sufficient computing power to process the computing operations required in real time with sufficient speed and accuracy. The microcontroller has access to internal or external memory ( RAM , ROM and flash memory ). With the usual quantities, ASICs are also used to relieve the microcontroller. However, it can also be advantageous to add FPGAs to motor controls , as these can perform some digital functions faster than the microcontroller. At the same time, FPGAs are flexible in their application and can be reconfigured using the software. However, they are not cost-neutral and can therefore be used sensibly for small quantities. The special feature of the engine control unit is that the programs that run cyclically on it do not all run at fixed time intervals, but some also run synchronously with the engine speed, for example to calculate the ignition point .

A characteristic feature of an engine control computer is the integrated interface for analog and digital input signals from sensors and output signals for actuators . There is a separate, prescribed and standardized interface ( K-line ) for on-board diagnosis so that the error memory can be read out with suitable devices . The engine control unit is often networked with other control units such as transmission control , ABS , ESP , instrument cluster and air conditioning via the CAN bus .

The engine control unit is often not an open control , but a closed control , because the ACTUAL state measured by a sensor is compared with a calculated target state ( feedback ) and the deviation in the closed control loop is then minimized via an actuator . The software in the engine control is also known as electronic engine management.

The engine control unit is usually installed in a protected location on the engine bulkhead or often towards the interior (under the dashboard). An engine control unit (after replacement engine and transmission) is usually one of the most expensive replacement parts in a car. This is mainly due to the fact that the control unit should function properly under difficult operating conditions, such as a very large temperature range, vibrations from the engine and shocks from the road conditions as well as overvoltage and undervoltage. It can often be delivered or repaired in exchange.

Function overview

The engine control unit is one of the most important control units in a motor vehicle. It does the calculations necessary to operate the engine in the vehicle.

Fuel injection

The fuel injection ensures the right amount of fuel at the right time , taking into account stored ignition maps . The calculation requires, among other things, the accelerator pedal position, the speed, the crankshaft angle, the available combustion air and the signal from the lambda probe.

Control of the throttle valve

The earlier Bowden cable has now been replaced by the electronic accelerator pedal (e-gas). Feedback of the throttle valve position to the engine control can be sent via an angle transmitter.

ignition

The ignition , described in a separate article, ignites the air / fuel mixture. The lambda control should set a suitable ratio of fuel and air in order to be able to operate the 3-way catalytic converter optimally.

Boost pressure control

If the engine z. B. charged with a turbocharger, the boost pressure must be regulated. The engine management system measures the boost pressure and adjusts an actuator on the turbocharger.

Regulation of the idle speed

The idle speed control adjusts the air and fuel quantities so that a constant speed is maintained without accelerating.

More functions

  • ECU self-diagnosis,
  • On-board diagnosis (OBD) for components that influence emissions (e.g. injection valves, lambda sensors, catalytic converters),
  • V-Max (electronically governed maximum speed),
  • Camshaft adjustment (in complex systems this can be done using its own control unit),
  • Exhaust gas recirculation control,
  • Catalyst heating,
  • Generator excitation,
  • Interaction with air conditioning , clutch of the air conditioning compressor,
  • Fan control,
  • Tank ventilation .

literature

  • Kai Borgeest: Electronics in vehicle technology , 3rd edition, Springer-Vieweg, ATZ / MTZ-Fachbuch, Wiesbaden 2014, ISBN 978-3-8348-1642-9
  • Robert Bosch GmbH (Ed.): Kraftfahrtechnisches Taschenbuch , 28th edition, Springer-Vieweg, Wiesbaden 2014, ISBN 978-3-658-03800-7
  • Konrad Reif: Bosch Autoelektrik und Autoelektronik , 6th edition, Springer-Vieweg, Wiesbaden 2011, ISBN 978-3-8348-1274-2

See also

Web links