Automatic Transmission

 

Automatic Transmission developed by Allison Transmission for this purpose. Automatic transmission work based on the planetary gear set. In order to understand this process let’s look at the basic parts of the planetary gear sets. Planetary gear sets have two input and one output. In automatic transmission the output rotation is drawn from the planet carrier. The two inputs are connected to the ring and sun gears. When the ring gear is stationery and rotation is given exclusive to the sun gear. This will cause to spin the ring gear also rotates. The ring and the sun gear rotates at the same speed. In this case the mechanism moves as a single unit. The ring gear speed is increased further. Turning the sun gear in the opposite direction will results in a reverse gear. So, the operation of automatic transmission is all about transmitting different rotation speeds into the ring and sun gears. The beauty of automatic transmission is that this speed variation can be transmitted simply by engaging few clutch packs. In an automatic transmission there is no direct connection between the input and the output shafts, rather there is an intermediate shaft between the two. In addition to clutch packs are used for transmitting power. Pressing the clutch packs together will lock the hub to the case. This is the simplest form of an automatic transmission. Let’s see how the first gear works. If the first clutch pack is applied the input shaft will connect to the intermediate shaft. On the other hand, if second clutch pack is applied the ring gear will connect to the case which will make the gear become stationary. In order to achieve the first gear just apply both the clutch packs together. You can note that the input shaft will turn the sun gear. Since the ring gear is stationary the output shaft will rotate with almost one third of the input speed. In order to achieve additional gear ratios at another planetary gear set. Applying clutch will always rotate both of sun gears at the input shaft speed. This planet carrier is permanently linked to the ring gear of first gear set. So, when C1 and C4 are applied together the ring gear of the output set will turn. Thus, as the output set the situation is like that at first gear except that have the ring gear will rotate as well. This means that the speed of the output planet carrier will increase. This is the second gear of the transmission. The planet carrier is also fitted with a hallow shaft. The shaft can be directly connected to the input shaft with the help of a rotating clutch module. With this setup we can get a direct drive. The ring and sun gears of the output set should rotate at the speed of input shaft. If we apply C1 and C2 the sun gear and ring gears will directly connect to the input shaft. In order to achieve 6^th gear just remove C1 and apply C4. At second set the input rotation is given to the carrier and the ring gear is stationary. This combination gives to the carrier and the ring gear is stationary. This combination gives a very high rotational speed to the sun gear. We can achieve a high over drive ratio at the output. Third planetary gear set is required to get the remaining gear ratios. The sun gear of this set is always connected to the input shaft. And here again the output of the set is connected to the input of the adjacent set. This means that applying 3 will always turn the ring gear of second set. For the remaining gear ratios C3 is always applied. For the the third gear just apply C1 as well. For the fifth gear remove C1 and apply C2. In order to go in reverse, apply thing ring gear clutch C5 as well. Since the planet gear of second gear cannot resolve they will spin. This will eventually lead to the reverse rotation of the sin gear. The final output will be a rotation in the opposite direction. A transmission control unit will decide when to apply which clutch pack.