Automatic transmission 2
kfz-tech.de/PME84
You have to carefully distinguish them from automated manual transmissions. Early on there were clutches that were engaged and disengaged by a servomotor. One of these received its signal by operating the gear lever.
With the VW Beetle, it could happen that the engine whined because your knee was too close to the gear lever.
kfz-tech.de/PME85
The initial starting clutch, which was closed by centrifugal force, had already been replaced by a torque converter in the Beetle. 'Semi-automatic' was actually the correct name for the design, while a dual clutch transmission
can already be described as an automated manual transmission or a true automatic.
The automatic torque converter must be strictly distinguished from this, even though you hardly notice the difference when driving. Closing the clutch after starting off sometimes makes it seem a little jerky like the dual clutch
transmission. But the name is deceptive, because the automatic torque converter looks completely different, and not just in the clutch bell.
kfz-tech.de/PME86
Due to the additional multi-plate clutches and planetary gear sets installed in the transmission, it looks like a large cylinder to the outside. However, a control with an oil pan is flanged on below. The oil pump is particularly
important here, usually with appropriate filtering. The oil can become very warm during operation and therefore has change intervals, although slightly longer than the engine.
kfz-tech.de/PME87
One of the planetary gears in such an automatic transmission consists of at least a sun gear in the middle and a ring gear on the outside. Between the two and meshing with both, two to four planetary gears.
Their carrier and the other two gears are usually connected to one shaft each, although a compact arrangement is necessary if there are more than two (picture above).
Now please imagine that the shaft for the sun gear comes from the motor, that of the planet gear carrier is solidly braked and the ring gear is connected to the final drive. That would be the realization of a small gear. If the
planetary gear carrier were then connected to the ring gear instead of being solidly braked, the ratio would be 1:1, i.e. a high gear.
And how does the control unit change the connections? The picture below basically shows how it can switch back and forth between two multi-plate clutches using oil pressure. For example, there is pressure on the upper
left line, which has a connection from the housing to a circumferential groove in the transmission shaft. Of course, to save space, the sealing is done using O-rings rather than the Simmerrings shown here.
kfz-tech.de/PME88
Basically you just need to understand how the pressure gets into a line of the rotating shaft. You also have to imagine the actuation of the multi-plate clutch as a ring piston. The connection is closed by the inner clutch and
thus to the corresponding shaft. If the right line at the top left is charged with pressure, there is from now a connection to the outer shaft on the right.
kfz-tech.de/PME89
This is where things get a little more complicated because you're trying to accommodate even more gears in a planetary gear set to save space. In principle, newer automatic transmissions require almost more space for
multi-plate clutches than for planetary gear sets, even though they are located one inside the other. Here, on the left, three waves come off above and below each other. With such an arrangement you can easily achieve 3
forward and one reverse gears.
| Of course, more gears also mean slightly more possible drive power. |
The whole thing used to work without electronics, but today a few more parameters can be incorporated into the control system. There was a lot of catching up to do with an automatic torque converter, especially in terms of
fuel consumption, where it now delivers impressive results, although it still lags slightly behind the manual transmission with the right driver.
kfz-tech.de/YME45
| Transmission flushing has been increasingly recommended since workshops have been able to
purchase flushing devices for relatively little money. |
kfz-tech.de/YME46
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