Patent ID: 8225691

Claim:
A gear pair constituted by a small diameter conical involute gear and a large diameter conical involute gear, wherein the conical involute gears each have helical teeth having an involute tooth profile and a spiral angle, wherein an addendum modification coefficient of each of the helical teeth is non-linearly changed in a face width direction of each of the conical involute gears, wherein the conical involute gears are engaged with each other, wherein the conical involute gears are each defined by an aggregate of a plurality of imaginary cylindrical gears, each of the imaginary cylindrical gears has an axis which is in parallel to a conical surface of the conical involute gears passing through a reference pitch point, each of the imaginary cylindrical gears has the same module, wherein in the case of setting the number of teeth of one of the conical involute gears to z, setting a conical angle of the one of the conical involute gears to δ, and setting the number of teeth of the imaginary cylindrical gears thereof to z v , setting a pressure angle of the imaginary cylindrical gears thereof to α v , setting a pressure angle of the imaginary cylindrical gears thereof in a vertical cross section of a tooth to α n , setting a module of the imaginary cylindrical gears thereof to m v , setting a spiral angle of a tooth to β, and setting a module of the imaginary cylindrical gears thereof in a vertical cross section of a tooth to m n , relational expressions z v =z /cos δ, m v =m n /cos β, and α v =tan −1 (tan α n /cos β) are satisfied, wherein in the case of setting one of the plurality of imaginary cylindrical gears so that the addendum modification coefficient amount is zero to a standard imaginary cylindrical gear, setting a pressure angle of the standard imaginary cylindrical gear to α v , setting an engagement pressure angle in a surface perpendicular to a conical line of one of the plurality of imaginary cylindrical gears to α v ′, setting an addendum modification coefficient of a smaller-diameter imaginary cylindrical gear to x 1 , setting an addendum modification coefficient of a larger-diameter imaginary cylindrical gear to x 2 , setting the number of teeth of the smaller-diameter imaginary cylindrical gear to z v1 , and setting the number of teeth of the larger-diameter imaginary cylindrical gear to z v2 , relational expression invα v ′=[2( x 1 +x 2 )/( z v1 +z v2 )] tan α v +invα v , x 1 =z v1 ( invα v ′−invα v )/2 tan α v =z v1 f ( invα v ′), and x 2 =z v2 ( invα v ′−invα v )/2 tan α v =z v2 f (invα v ′) are satisfied, wherein the addendum modification coefficients of the small diameter conical involute gear and the large diameter conical involute gear are obtained by the relational expressions.