An approach based on the minimum amplitude of loaded transmission error of drive gears was proposed to reduce vibration and noise.The modified tooth surfaces were represented by a sum of two vector functions that determine the theoretical tooth surface and deviation surface fitted by triple B splines based on tooth surface mesh data from the curves created by double parabolas and a straight line

including: profiled

longitudinal and both profiled and longitudinal curves;and normal vector of the deviation surface was deduced.Besides

LTCA was applied to the modification technology

and genetic algorithm was used to optimize the parameter of curve

and draw up a set of calculation procedures simulating TCA and LTCA of the modified helical gears.The results show that the loaded transmission error represents a linear increase in amplitude with the increasing load on theoretical tooth gears

however

its amplitude come into fluctuations and finally tends to be stable due to increasing contact ratio with the increasing load on modified gears

thus providing a new method for optimal design of modified helical gear tooth surfaces.