Conventional planetary drives come in either a two or three stage configuration. A two-stage configuration offers reduction ratios from 16:1 to 60:1. A three-stage planetary drive has reduction ratios from 66:1 to 215:1. The GFT 45 T2/T3 from Rexroth, Bosch Group, however, is both a two- and three-stage planetary drive. As a two-stage drive, it handles low-ratio (high-speed) operation. Its third stage can be engaged for high-ratio (low-speed) operation. Maximum intermittent output torque is 45,000 Nm (33,188 ft-lb) with a maximum output speed of 150 rpm.

The dual-ratio design offers four advantages:
•  A wide operable speed range.  
•  Two reduction ratios in a single unit.
•  Shift-on-the-fly between reduction ratios.  
•  High-speed operation without an external cooling circuit.

The high ratio is achieved through the input stage, which can be disengaged when the low ratio is required. The input stage will increase the low ratio by approximately four times, for a high ratio that is approximately four times the low ratio. The input stage is engaged and disengaged by use of two clutch packs made of sintered outer disks and metal inner disks. The two clutch packs are spring applied and hydraulically released and also serve as a static emergency/parking brake. There is a separate hydraulic release port for each clutch pack.

There are four possible clutch pack position combinations.
•  With no pressure applied to either clutch pack, the drive is in the braked position. Both clutch
    packs are engaged by spring force.
•  With pressure applied to both clutch packs, the drive is in the free-wheel condition. The drive
    speed is limited in this condition.
•  With pressure applied to the inner clutch pack and no pressure applied to the outer clutch pack, the drive will operate in the high ratio, low speed mode. The inner clutch pack is released for driving through the input stage while the outer clutch pack is engaged to secure the input stage ring gear to the stationary spindle.
•  With pressure applied to the outer clutch pack and no pressure applied to the inner clutch pack, the drive will operate in the low ratio, high speed mode. The outer clutch pack is released to allow rotation of the input stage ring gear while the inner clutch pack is engaged to secure the input shaft to the input stage ring gear.

Rexroth, Bosch Group
www.boschrexroth-us.com