Patent ID: 7870785

Claim:
A positive displacement flowmeter provided with a pair of non-circular gears in a casing, wherein the pair of the non-circular gears has an oval pitch curve itself having a locus of a contact point on a pitch line as a tooth profile curve and satisfies conditions of r 1 1+ r 2 =K=const ., and r 1 ·dθ 1 =r 2 ·dθ 2 , and a moving radius of the oval pitch curve is represented by r 1 =a/(1−b cos nθ 1 ) (i=1, 2) (where r i (i=1, 2) denotes a moving radius that is a distance from the rotation center to the oval pitch curve, and a, b, n and θ i (i=1, 2) denote similarity coefficient, flattening, number of lobes, and moving angle, respectively).