Gerotor pump with ceramic ring

A gerotor pump for coupling to an auxiliary power unit mounted in an aircraft comprising:

• a housing having an inlet and exit port in fluid communication with a chamber therein;
• a shaft journalled in the housing and extending through said chamber;
• a first metallic port plate supported by a first bearing mounted on said shaft;
• a second metallic port plate supported by a second bearing mounted on said shaft and axially spaced from said first port plate;
• a first metallic gear having external teeth and mounted for rotation to said shaft;
• a second metallic gear having internal teeth in meshing engagement with said external teeth, said first and second gears disposed between and axially spaced from said first and second port plates to define an axial clearance;
• and
• a ceramic eccentric ring circumscribing said second gear to define a diametral clearance, and mounted between said port plates so that under cold soak conditions said diametral and axial clearances are sufficiently large so that the time it takes said auxiliary power unit to reach ten percent of its operating speed is shorter in comparison with said auxiliary power unit having a gerotor pump with a metallic eccentric ring.