Gear sets

The eight forward gears and the reverse gear are generated by four single planetary gear sets. The two front gear sets have one single common sun gear. The others have one sun gear each.

The following information applies to planetary gear trains in general:

If two components of the same gear set (sun gear, planet spider or ring gear) are running at the same speed, this gear set is in block operation. The individual components are not moving with relation to each other but they rotate together around the center axis.

If, for example, multidisc clutch E is closed, the sun gear and the ring gear of the gear set are rotating at the same speed. The planetary gears do not wear off. The planet spider also rotates with the same speed. The sun gears of the gear sets are supported on the transmission input shaft so they can rotate freely. The following rigid connections can be established in addition to those by the clutches:

• Planet spider 2 with transmission input shaft
• Planet spider 1 with ring gear 4
• Ring gear 2 with sun gear 3
• Ring gear 3 with sun gear 4
• Planet spider 4 with output shaft

One or more paths are created by shifting the shift elements and the mechanical connections of different components in the automatic transmission. These paths transmit the drive torque and transmission subsequently develops.

Fig 1: Identifying Gear Set Components

Courtesy of BMW OF NORTH AMERICA, INC.