Quasi-kinematic Couplings for Precision Automotive Assemblies

There are an innumerable number of precision automotive assemblies which use pinned joints for alignment. Many of these suffer from poor performance and cost/quality issues because pinned joints are inherently over-constrained. This paper introduces the Quasi-Kinematic Coupling (QKC) as a solution for precision (better than 10 microns) automotive assemblies. For these applications, QKCs require fewer parts, have a lower total cost, and provide submicron repeatability. This paper covers design and manufacturing considerations for automotive QKCs. Proof of concept is demonstrated via a case study on the block-main bearing assembly of a Ford six cylinder engine. Repeatability tests yield average QKC bearing center line repeatability of 0.65 microns at the outer journal bearings as compared to 4.85 microns for pinned joints. This QKC uses 60% fewer precision features, costs 36% less, and allows feature size and placement tolerance ranges which are twice as wide as those of the previous pinned joints. NOMENCLATURE Gmax Maximum gap between block and bedplate Gmin Minimum gap between block and bedplate Ka Stiffness in axial direction Kc Stiffness perpendicular to bearing center line Ra Repeatability in axial direction Rc Repeatability perpendicular to bearing center line δa Alignment error in axial direction δc Alignment error perpendicular to bearing center line δGMS Gap margin of safety δv Controllable gap variation