Review and kinematics of Rzeppa-type homokinetic joints with straight crossed tracks

After a discussion on basic kinematics and mechanics of Rzeppa type ball joints, the paper focuses on some design solutions provided by the patent literature. In particular a short patent review is carried out. Under ideal conditions the joint is homokinetic. However, geometry errors are inevitably present and nonhomokineticity induces torsional vibrations along the powertrain. For design purposes, the modeling of these effects at kinematics level is first required. In this paper an analytical procedure for kinematic analysis of ball joints with straight crossed tracks is proposed. The relationship between the rotations of the driving and driven shafts has been expressed as a fourth degree polynomial. This allows an accurate closed form solution, also in the case of the presence of geometry errors. By means of this procedure, that could be extended to other joint morphologies, the influence of manufacturing errors on the kinematics can be accurately investigated. The sensitivity coefficients of the transmission ratio with respect to the different ball joint geometry parameters can be also readily obtained. A numerical example shows the results obtained by applying the proposed method to a common type of industrial ball joint with geometric errors.