A gear with translational wheel for a variable transmission ratio and applications to steering box

The paper presents the geometric and functional characteristics of a gear with ascending variable ratio, based on the gear with rack and geared segment. This gear can be used for the steering boxes of some low power vehicles (without servo-system). The steering gearbox requires an increase (around 30%) in the transmission ratio from the middle position (rectilinear displacement of the vehicle) to the extreme positions (turning/avoiding obstacles/parking). The rack nut is transformed in a translational wheel, while the geared segment is eccentrically articulated. The paper presents the motion functions, in analytical and graphical form, important conclusions being drawn on the influence of some parameters (such as number of teeth of the translating wheel and eccentricity of the geared segment). The paper analyses the correlation of these parameters to obtain the required increasing in transmission ratio, in terms of ensuring good gearing conditions (the variation of the distances between axes, the variation of the clearance between teeth).

► We analyze the geometric-functional characteristics of a gear with variable ratio. ► We develop a model for defining the motion function of the gearbox. ► We analyze the conditions to obtain the required increasing in transmission ratio. ► The proposed gear assures good precision and reversibility characteristics. ► The variation of the clearance between teeth is very small.