Crescent gear pump with hypo cycloidal and epi cycloidal tooth shapes

In a crescent pump gear including:

• (a) housing means having a chamber communicating with an intake port and a discharge port;
• (b) shaft means journaled for rotation within said chamber;
• (c) externally toothed inner gear means mounted centrally on said shaft means about a first axis;
• (d) internally toothed annular gear means eccentrically mounted for rotatable engagement with said inner gear means about a second axis;
• (e) crescent means contacting a portion of said inner and outer gear means;
• (f) said inner gear means having dual cycloidal tooth profiles generated about a first generating circle, and said outer gear means having dual cycloidal toothed profiles generated about a second generating circle.

In a method of producing tooth profiles of externally toothed inner gears eccentrically offset and engageable with internally toothed annular outer gears, said inner and outer gears contacting a crescent having an inner crescent radius and an outer crescent radius, said method including the steps of:

• (a) generating the pitch circle of said outer gear;
• (b) producing an epi cycloid of a first cycloid set by rolling said epi cycloid in a clockwise direction about the pitch circle of said outer gear starting at the vertical axis for a full 180.degree. of roll;
• (c) producing a hypo cycloid of a first cycloid set by rolling in a counterclockwise direction around said pitch circle of said outer gear starting at the vertical axis until the generated curve intersects at said outer crescent radius;
• (d) producing an epi cycloid of a second cycloid set by rolling in a counterclockwise direction about said pitch circle of said outer gear starting at an angle from the vertical axis equal to 360.degree. divided by the number of teeth of said outer gear minus two times the angle resulting from the length of roll of said first epi cycloid roll for a complete 180.degree.;
• (e) producing a hypo cycloid of a second cycloid set by rolling in a clockwise direction about said pitch circle of said outergear starting at an angle from the vertical axis equal to 360.degree. divided by the number of teeth on said outer gear minus two times the angle resulting from the roll of said first epi cycloid roll until the generated curve intersects said outer crescent radius;
• (f) connecting the resulting gear profiles with an arc slightly offset from said outer crescent radius in order to provide running clearance;
• (g) copying the resulting gear form about the centre of said pitch circle of said outer gear at increments equal to 360.degree. divided by the number of teeth of said outer gear;
• (h) generating the pitch circle of said inner gear;
• (i) producing an epi cycloid of a first cycloid set by rolling said epi cycloid in a clockwise direction about said pitch circle of said inner gear by starting at the vertical axis of said pitch circle of said inner gear until the generated curve intersects said inner crescent radius;
• (j) producing a hypo cycloid of a first cycloid set by rolling in a counterclockwise direction about said pitch circle of said inner gear by starting at the vertical axis until the generated curve is slightly smaller in length than said hypo cycloid curve generated on said outer gear;
• (k) producing an epi cycloid of a second cycloid set by rolling in a clockwise direction about said pitch circle of said inner gear starting at an angle from the vertical axis equal to 360.degree. divided by the number of teeth on said inner gear minus two times the angle resulting from a full 180.degree. theoretical roll of said first epi cycloid until the generated curve intersects at inner crescent radius;
• (l) providing a hypo cycloid of a second cycloid set by rolling in a clockwise direction around the pitch circle of said inner gear starting at an angle from the vertical axis equal to 360.degree. divided by the number of teeth on the inner gear minus two times the angle resulting from the full 180.degree. theoretical roll of said first epi cycloid until the generated curve is slightly smaller in length than the hypo cycloid curve generated on the outer gear and is equal in length to the hypo cycloid curve generated by said first cycloid set;
• (m) connecting the resulting gear profiles with an arc offset slightly from the connecting arc on the outer gear set to provide a running clearance;
• (n) copying the resulting gear form about the centre of said pitch circle of said inner gear at increments equal to 360.degree. divided by the number of teeth of said inner gear;
• (o) connecting the gaps left between said epi cycloids with an arc slightly smaller than the inner crescent arc in order to provide running clearance.