Design of a compliant revolute mechanism for accurate dynamic characterization of automotive steering columns

It is difficult to obtain accurate measurements of the dynamic characteristics exhibited by automotive steering columns. The difficulties are due in-part to the use of lubricated contact bearings which support the column during testing. These bearings introduce damping, hysteresis, non-linear stiffness and clearance/preloaded constraints on the column. These error sources then mask the true dynamic behavior of the column, thereby preventing a better understanding of the relationship between column design, manufacturing tolerances and column vibration. With this paper, we introduce the concept of a revolute compliant mechanism that can be used in place of contact bearings to support steering columns during dynamic tests. These mechanisms do not exhibit the non-linear damping/stiffness and non-repeatable errors found in contact bearings. As a result, they can be used to design equipment that is capable of taking test data which matches theoretical predictions to within 2%. Experimental results obtained with this equipment suggest (more study is needed to confirm this) that manufacturing errors may be responsible for up to 20-30% error in predicting vibration amplitudes of components within the column, but only 2% error in predicting steering wheel vibration amplitude. Understanding this tolerance-response relationship (via this test equipment) is a necessary first step in understanding and eliminating steering wheel nibble vibrations.