The invention provides a lightweight design method of a high-torsional-rigidity
drive shaft. The lightweight design method of the high-torsional-rigidity
drive shaft comprises the following steps: designing a
drive shaft into a hollow rotary
forging shaft, calculating the maximal outer diameters of two performance constraint sections of the drive shaft, and simplifying the drive shaft into a three-section-type stepped shaft, wherein the relatively small maximal outer
diameter of two performance constraint sections as the two-end-section outer
diameter; designing the intermediate section outer
diameter with the aim that the outer diameter of the intermediate section is maximized by combining the outer
peripheral rotation space of the intermediate section of the drive shaft according to the constraint condition that the outer diameter of the intermediate section of the drive shaft is not greater than twice of the outer diameter of the sections at two ends; and designing the inner diameter and the weight losing ratio of each section of the three-section-type stepped shaft according to the allowable torque intensity value of raw materials of the rotary
forging shaft and the required torque intensity improvement ratio. Compared with a
solid shaft in the prior art, according to the method, the torque rigidity of the drive shaft can be improved by 60% approximately, and meanwhile the weight can be lost by 20%, so that the horizontal finished automobile control stability is improved with the minimum cost; the torque vibration of a drive
system is improved; the vehicle comfort is improved.