Variable Rotor Speed Transmission With High Speed Traction Drive

In order to reduce a helicopter’s rotor noise, a research on variable rotor speed transmission (VRST) was started in 1994. The VRST is equipped with a power split type continuously variable transmission (CVT) which consists of a high speed traction drive variator (half toroidal type) and a planetary differential gear unit. With this system, the rotor speed can be variable from 85% to 100% of its rated rpm continuously and 5 dB noise reduction can be expected. Since the weight and size reduction of this CVT system is mandatory for a helicopter application, the traction drive is driven with 23,000 rpm input speed to reduce the torque, which is three times as high speed as existing automotive application. To substantiate this high speed traction drive, a rig test was conducted and expected power transmitting capability under 23,000 rpm has been demonstrated.