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How do we make control systems

6/14/2013 | Words: Lucie Maluck | Pictures: Robert Hack

electronics

What distinguishes a good engine? Very high injection pressures? Precisely designed and manufactured components? Low-soot combustion? The answer is all of those things – though the really decisive factor is the interaction between them. And controlling and monitoring that interplay is a key engine technology. The engine management system is the brains of the engine that controls key systems such as fuel injection, turbocharging and exhaust gas recirculation. That makes it so important that it is produced in-house at MTU rather than bought in from an outside supplier.

An air-conditioned room, staff in white lab coats and a soft humming sound. Is this what you would imagine an engine factory to look like? It sounds more like a dental surgery. But this large, sterile room is the MTU Electronics Center. Clicking and clacking sounds emanate from a large white robot. With micrometer accuracy, a pick-and-place machine precisely places tiny components weighing hardly five milligrams, such as capacitors, resistors and diodes, on a printed circuit board. Depending on the control unit, a circuit board can have anything from 1,500 to 2,000 components that are placed on the board from large reels and then soldered in position. In that way, a bare green circuit board can be made into a virtually complete printed circuit assembly in just a few minutes. At this stage, however, it is not quite the finished article – it still has to be X-rayed and have ist final few large components fitted by hand. The subsequent visual inspection is also an integral part of the production process. Every single one of the less than pinhead-sized components has to be firmly fixed in the right place. "In the tough conditions that diesel engines are asked to operate in on a daily basis, we have to be able to rely on the control system," explains Heinrich Dageförde, the man in charge of control unit production at MTU.

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Tiny signal, massive effect
Say, for example, a haul truck driver wants the vehicle to go faster. He presses on the accelerator, very probably unaware of the complex electronic processes he is initiating by doing so. The processor – the central component of any control unit – reads the accelerator position from a sensor input channel. To the processor, more power means that more fuel and air have to be delivered to the cylinders. It also has to increase the fuel pressure so that the fuel atomizes better. So it computes the precise quantity of fuel that must be injected into the combustion chamber, lengthens the time that the injectors remain open to inject the fuel and opens the air valves. And as a certain quantity of exhaust is always added to the fuel-and-air mixture on modern MTU engines to minimize the nitrogen oxide emissions, the processor also calculates how much exhaust to recirculate, which it does with the aid of data from sensors in the charge-air pipe. It then passes the resulting instructions to the actuators via a data bus. They convert the electrical signals from the processor into mechanical movements. In this instance, they move the air and EGR valves and apply the electrical current to the fuel injectors for a longer period.

Like a dental surgery
A highly complex process. And it reveals only a fraction of the parameters that the processor has to control. In all, the CPU has to process as many as 60,000 settings. The software for it is created by MTU developers. They write the control algorithms that calculate how the engine should respond to the signals from the sensors. And so that those signals are correctly received and relayed by each individual small component, meticulous attention is paid to every detail in production. The pick-and-place machine is housed in an air-conditioned room with a controlled temperature of 22°C where all the sta" wear white lab coats – rather like in a dental surgery. But these lab coats contain special metal fibers because the electronic components are electrostatically sensitive. So sensitive that the room also has a special floor covering to prevent the components becoming statically charged. Pretty complex things, these control systems. Probably not what the haul truck driver is thinking of when he presses on the accelerator.

The content of the stories reflects the status as of the respective date of publication. They are not updated. Further developments are therefore not taken into account.

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