 ZF Hairpin technology
kfz-tech.de/Ye246
With the appearance of the reluctance motor, one might have thought that the development of electric motors for electric vehicles had reached a long-term end point. And yet the Zahnradfabrik F
riedrichshafen
has proven us wrong.
The basic problem is clear. There is a part inside, the rotor, which is supposed to rotate with the help of electrical energy. For this to happen, a certain amount of magnetism must be present, which is supported by the
magnetism generated in the housing and is driven forward by it, so to speak.
In the past, people only worked with electromagnets, both inside and out. This means that the motor consisted only of easily magnetizable material in both the rotor and the stator with windings through which current
flowed,
both electrically separated from each other.
There was no component that was inherently magnetic, either inside or outside. Now comes the problem: if you connect both parts to electricity, the rotor will at best give a jolt and then stop, if necessary forever.
In order for it to continue, something has to change. There used to be a so-called commutator for this. At the end of the rotor, just before the bearing, it consisted of a slip ring that was electrically divided several times, onto
which two carbon brushes were pressed with spring force.
In this way, the current fed into the rotor could always be guided, depending on its position, in such a way that the electromagnetic attraction was always passed on from one E-magnet to the other, i.e. it never stopped as
long as current flowed to the rotor and the stator.
The point where the carbon brushes rubbed against the split copper ring was of course a potential wear point. People wanted to get rid of this. And that was exactly the starting point for the synchronous motor. No more
commutator, just permanent magnets in the rotor.
The movement was now generated by alternately controlling electromagnets in the rotor. You might think that this solved the problem. However, the magnet inside turned out to be a disadvantage. It was best to make it
from
a material that is a rare earth element.
There are also problems if the motor is de-energized and is driven by another motor, e.g. on a different axle. Then electricity is generated here, perhaps even with warming, which is totally undesirable. Then, in addition to
the
vehicle, an engine that is actually not running is also driven.
Yes, there are solutions for this too: A copper cage is constructed into the rotor without magnets and therefore rare earths and is magnetized by a type of induction coming from the housing. Otherwise, the stator remains
as
it is.
Another design, the reluctance motor, attempts to direct the magnetism to the exact places where it is most efficient by shaping the metals in the rotor in a special way. Tesla still adds small magnets, however.
And now comes the main technological leap from ZF. There they are going back to the electric motor with a commutator. This means that current is brought from the outside into the rotor, which therefore does not need any
magnets, and to exactly the right places.
And how does ZF avoid friction and wear on the commutator and also gain in length? By using the principle of induction. No friction from carbon brushes, but a type of sensor, one side of which brushes closely past the
former slip ring inside and the other outside.
So there is no contact or friction and yet electricity is transferred to a rotating part. What might be lost through induction is gained through the lack of friction. No rare earths required, geopolitically safe because the raw
materials can be obtained via shorter routes.
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