Simpson Gear Set

The Simpson Gear Set is one of the early variations on the simple set. It is capable of 3 forward gears and one reverse. On BMW transmissions, the Simpson Gear set is used in the 4HP transmission which is a four speed automatic. Fourth gear (overdrive) is obtained by the addition of an auxiliary gear set (simple).

Characteristics of the Simpson Gear set are as follows:

• Two Internal Ring Gears, one rear input ring and one attached to the rear planetary carrier.
• Two Planetary carriers, each containing three planetary pinions.
• One common Sun gear, which meshes with both sets of planetary pinions.
  Fig 1: Identifying Simpson Gear Set

  Courtesy of BMW OF NORTH AMERICA, INC.