Modeling and Design of Air Vane Motors for Minimal Torque Ripples

This paper presents the analysis and design of a novel air vane motor. Air motors produce very high specific power. They require compressed air rather than electricity; thus avoid sparks and can be used in demanding environments. Same as other types of rotary machines, air vane motors exhibit torque fluctuations. The varying torque curve is a result of unmatched torques generated by the vanes in one revolution. Torque fluctuations produce dynamic speed ripples that further introduce undesirable vibration. Rather than using auxiliary flywheels to smoothen the fluctuation, we propose a new stator configuration that can help produce a nearly constant output torque. The stator adopts asymmetric inlet/outlet positions and a noncircular inner profile. Through numerical optimizations of the noncircular profile, the torque fluctuation and speed ripples are greatly reduced, when compared with traditional air vane motors with circular stator profiles. Meanwhile, the air vane motors can be more efficient by setting a reasonably higher expansion ratio. We expect that the optimized noncircular stator profile can be applied to air vane motors of various sizes to eliminate rotating vibrations.