Automatic transmission 1
We already discussed an automatic transmission in the previous chapter, the dual clutch transmission. The rest are usually called 'converter automatic' because they are combined with a torque converter. This does not
necessarily have to be the case, such as Toyota has demonstrated with the Prius.
The structure and function of the torque converter are among the most difficult issues in the automotive sector. This is due to its power transmission through oil flows. No, not lines, but flows directed by guide vanes, which
not only transmit torque, but also amplify it.
kfz-tech.de/PME80
Even the construction with a basically rotating oil container (picture above) is rather unusual. It is usually just about half full, with the oil naturally leaning against the cladding as a kind of ring. Although the pump wheel rotates
at the same speed as the crankshaft, it is located on the gearbox side.
kfz-tech.de/PME81
Here is a view of the side of the pump wheel that is open towards the engine. Ignore the center and start your thinking with the many elongated vanes that taper inwards. They reappear on the outside after disappearing
behind the middle part.
Now you have to look closely, possibly enlarge the picture. You may recognize this middle field, which turns out to be a semicircle. The second part of the semicircle is integrated into the turbine wheel, here shown to the left
of it. The oil driven by the impeller encounters the turbine wheel directly.
The vanes pick up the oil on the inside, accelerate it and direct it on the outside onto the turbine wheel with significantly more pressure. In the picture below you can see it with the second part of the semicircle. It is part of the
casing, not free to rotate in it like the pump wheel. The toothing connect to the transmission input shaft.
kfz-tech.de/PME82
No, the oil does not flow directly back from the turbine wheel to the pump wheel. Then there is the so-called guide wheel in between, which, in contrast to the other two wheels, is fixed as long as how, by reversing the flow of
oil on the way back to the pump wheel, it can drive it a little bit too.
It increases the torque by redirecting the oil in the direction of rotation of the pump wheel. It even replaces a gear in a certain engine speed range with great success. With increasing engine speed, however, it would impede
the flow of oil, which is why it is allowed to run with the two wheels via a free-wheel.
kfz-tech.de/PME83
Oil flows naturally allow slip. That is why there is a so-called single or even multi-disk 'lock-up clutch' in all modern converters. Above you can see all the parts of the torque converter assembled again, the lock-up clutch on
the far left.
It connects the pump and turbine wheel with each other and separates them only when moving off and sometimes also when changing gear (converter area). It is operated by the flow of oil that is continuously exchanged
in the converter area. The lock-up clutch is actuated by reversing and thus stopping the flow of oil.
kfz-tech.de/YME44
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