Abstract: A cylindrical gear wheel having helical teeth with different pitch diameters for the left hand and right hand sides of the teeth and convergent line of teeth in which one side of the teeth are characterized by positive values of addendum modification while the other side of the teeth has negative values of addendum modification. By positive addendum modification is meant an addition to the nominal pitch diameter to obtain the pitch diameter at one side of a tooth and by negative addendum modification is meant a substration from the nominal pitch diameter to obtain the pitch diameter of the other side of the tooth. In the range of normal values of tooth pitch (mn) from 2 to 6 mm or normal tooth module the angular difference of inclination between the left hand and right hand sides of the teeth is within the range of 30' to 3.degree. for pitch diameters up to 500 mn and the addendum modification values are in the range from 0.01 to 4 mn.

Abstract: A cylindrical gear train comprising first and second gears having helical eth of different thickness with different pitch diameters for the left hand and right hand sides of the teeth and with different nominal angles of inclination and different mesh correction for the mating left hand and right hand flanks of the teeth. Within the normal module range of m.sub.n =2-6 mm, corresponding to the normal module range of 2.pi.(mm) to 6.pi.(mm), and for pitch diameters up to 500 mm, the maximum tooth convergency is 3.degree. and the addendum modification coefficient does not exceed 0.8.