Friction drive is a mechanical device that utilizes friction force to transmit torque and power. Since the power is transferred through shearing a thin layer of highly pressurized lubricant film formed between the mating surfaces. Friction drive possesses desired performance attributes that pertain to its unique operating principles. These attributes include high mechanical efficiency, minimal backlash, low noise and vibration and high-speed capability. The power density of a friction drive can be very high when operated at elevated speeds. These performance features, in conjunction with its inherent manufacturing simplicity, make friction drives suitable candidates for a host of applications. The current global technology trend towards electrification and increasing use of electric machines in auxiliary drives for both automotive and industrial applications presents a good opportunity for friction drives as a cost-effective alternative to conventional gear drives. The smooth high-speed performance feature of friction drives allows the use of more efficient high-speed motors to reduce motor size and thus improve system power density A novel cylindrical friction drive was developed for electric oil pump applications. The friction drive is to be integrated with an electric motor to provide necessary speed reduction. The friction drive, as shown in Figure 1, is comprised of an outer ring, a sun roller, a loading planet, two supporting planets and a stationary carrier. The sun roller is set eccentric to the outer ring to generate a wedge gap that facilitates a torque actuated loading mechanism for the friction drive. The loading planet is properly assembled in the wedge gap with frictional contact with the sun roller and the outer ring and is elastically supported on the carrier. By altering the ratio of the support stiffness to contact stiffness, the actual operating friction coefficient of the friction drive can be changed to suit for desired performance regardless the wedge angle. This provides a grater freedom for design optimization.
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