Patent ID: 8827668

Claim:
A tooth profile for rotors of a positive displacement gear pump with external helical teeth gear wheels, comprising: an inactive tooth top profile, an inactive tooth bottom profile, an active right-handed tooth flank profile and an active left-handed flank profile, wherein said active right and left-handed tooth flank profiles are stub-tooth involute profiles and said inactive tooth top and bottom profiles are defined by circular arcs wherein the active stub-tooth involute profile has a transverse contact ratio or continuity (ε t ) from 0.4 to 0.45, and the helical teeth gear has an helical contact ratio or continuity (ε β ) from 0.6 to 0.85, said circular arches of inactive tooth top and bottom profiles have a centre (O f , O t ) and radius (r f , r t ) defined by the following equations: { O f = H f + ( H f - O ) · Δ ⁢ ⁢ R  H f - O  r f =  P f - O f  ⁢ ⁢ and ⁢ ⁢ { O t = H t + ( O - H t ) · ζ · Δ ⁢ ⁢ R  H t - O  r t =  P t - O t  with (ζ=[1.1÷1.6]) Δ R= 0.5*(| H t −K t |+|H f −K f |) wherein O is the centre of the primitive circumference (p) of the gear; H f is a point on the primitive circumference on the radial direction (r-v) of the centre line of the space between two contiguous teeth; P f is a point at the end of the involute segment near the beginning of the tooth root section; K f is a point identified by the intersection of the normal and the involute profile in point P f and the radial direction (r-v) of the centre line of the space between two contiguous teeth, H t is a point on the primitive circumference on the radial direction (r-v) of the centre line of the tooth; P t is a point at the end of the involute segment near the beginning of the tooth top section; K t is a point identified by the intersection between the normal and the involute profile in point P t of the segment and the radial direction (r-d) of the centre line of the tooth.