D.he shift to electromobility brings some changes with it. In the German automotive industry, 180,000 jobs are on the brink, 95,000 of them with suppliers who currently produce engine and transmission parts. This is the result of a study published at the beginning of July by Agora Verkehrswende and Boston Consulting. Although the authors calculate that a similar number of jobs will be created in other industries or companies, this may not be of much comfort to high-earning metal workers. For some time now, major suppliers have been trying to make a virtue out of necessity and are investing in the development of electric drives. But do they offer sufficient technical differentiation potential so that German companies with their cost structure have a chance against Chinese competitors?
At least Bosch and Mahle, Swabian foundation companies that do not have to orientate themselves on the short-term capital market, are taking up the fight. In the past few weeks you have presented new developments in which European engineering art manifests itself. Mahle presented a new type of separately excited synchronous motor that works without sliding contacts. The associated leap in innovation is roughly as large as that from intake manifold to gasoline direct injection. The best way to understand it is to take a look at the machinery that is currently available to the developers of electric cars. The permanent magnet synchronous machine, as used by Porsche, for example, offers the highest power density. In such a motor, magnetic materials in the rotor ensure that the rotor rotates as soon as the stator is supplied with alternating current. As soon as the nominal power is reached, however, the magnetic field must be actively weakened, which worsens the efficiency at high speeds. In addition, the permanent arousal is associated with considerable use of resources. Because in a single 140 kilowatt motor there are around two kilos of magnetic material, including the rare earths neodymium and dysprosium.
The widespread asynchronous machines in which a current flow is induced in the windings of the rotor are therefore less expensive. Especially at low speeds, the efficiency is significantly worse than with permanently excited motors.
Separately excited synchronous machine
A third alternative is to use an electromagnet as the rotor, i.e. a single coil with a ferritic core. This so-called separately excited synchronous machine, on which the Renault Zoe relies, impresses – compared to the asynchronous machine – with a significantly higher degree of efficiency, since only one to three percent of the total power is required for the rotor excitation. However, this type of machine has so far had one major disadvantage: the current required for magnetization flows into the rotor via sliding contacts. What grinds creates friction and wear. Mahle has now found a way to transmit electricity without contact. A small rotary transformer, which is firmly connected to the stator, is used for this. A second winding, to which the current is inductively transmitted, is located on the rotor side. The component itself is inconspicuous and hardly bigger than a coffee cup. And yet there is considerable manufacturing knowledge in the control: namely, the transmission is via alternating current, so the motor output can be regulated via a phase shift. The current arriving on the rotor side is then converted back into the direct current required by the electromagnet.
The losses that occur are small. The map published by Mahle shows an efficiency of more than 94 percent not only in the best point, but over a wide speed range. “This allows you to achieve a greater range, regardless of your personal driving profile,” explains Martin Berger, head of research at the company. Since many car manufacturers want to build their own electric motors, Mahle not only offers the complete motor, but also wants to sell the inductive power transmitter as a separate component from the supplier. “That would then be the crankshaft for the electric motor,” says Berger. It will be years before the engine finds its way into a first production car.