Analysis of Ball CV-joints of Fixed Type

Abstract: Two theoretical models for analysing ball CV-joints of fixed type are presented. The models, which have been implemented in computer programs, calculate internal conditions such as load distribution, contact angles and displacements for different operating conditions. Both models can handle statically indeterminate joints as well as clearance and some types of tolerances. The joint components are assumed to be structurally rigid; only contact deformations are considered. Additionally, inertia forces are neglected.

In the first model, friction forces are neglected. The second model is an extension of the first one and includes friction forces as well as truncated contacts. The efficiency of power transmission is also calculated. It is important to know the internal load distribution under different operating conditions, since it strongly influences the fatigue life. It is also always desirable to increase the efficiency of the joint. The models can be useful tools for product development and optimization of joint design.

Since the problem in general is statically indeterminate, displacements for the joint components are introduced as unknown variables. By using geometrical compatibility and constitutive relations, the solutions are obtained when the equilibrium conditions are fulfilled. The efficiency is obtained as the ratio between the output torque and the input torque. The models lead to systems of non-linear equations, which are solved numerically.

A comparison of the two models shows that the frictional forces seem to have a large influence on the contact forces, especially for low working angles. Even at angles as low as 2l = 2o, the maximum contact force is more than twice the nominal contact force (contact force at 2l = 0 ==> no friction is developed). The efficiency decreases rapidly for increasing working angles.