Pneumatic vane-type motor with bearing ring for vane tips

A pneumatic vane-type motor for a dental handpiece to drive a dental tool, comprising:

• a sleeve-shaped motor housing located in the outer surface of said handpiece and forming a stator;
• a circular-cylindrical inner surface of said housing;
• a rotor within said inner surface and having a rotary axis parallel to the axis of said cylindrical inner surface, said axes being spaced apart;
• a power take-off shaft connected to clutch means for driving said dental tool;
• axially extending grooves in said rotor;
• rotor vanes radially and movably mounted in said grooves and extending with their outer ends towards said circular cylindrical inner surface;
• air inlet means for compressed air and air outlet means discharging into a space between said rotor and said circular cylindrical inner surface;
• a bearing ring located between said circular cylindrical inner surface and said outer ends of said rotor vanes, said bearing ring being freely rotatable and coaxial with said inner surface;
• said bearing ring having an inner surface contacting said vanes at their outer ends in said axial grooves;
• annular gap means located between said bearing ring and said circular cylindrical inner surface, said annular gap means comprising an air cushion bearing for said bearing ring and receiving compressed air via a plurality of circumferentially spaced passages in said motor housing;
• a compressed-air supply line and a branch line;
• said passages being connected via said branch line to said compressed-air supply line, said air supply line supplying said air inlet means, said air inlet means discharging into said space between said rotor and said circular cylindrical inner surface.