The automotive industry is continuously striving to reduce vehicle mass by reducing the mass of components including wheel bearings. A typical wheel bearing assembly is mostly steel, including both the wheel and knuckle mounting flanges. Mass optimization of the wheel hub has traditionally been accomplished by reducing the cross-sectional thickness of these components. Recently bearing suppliers have also investigated the use of alternative materials. While bearing component performance is verified through analysis and testing by the supplier, additional effects from system integration and performance over time also need to be comprehended.
In a recent new vehicle architecture, the wheel bearing hub flange was reduced to optimize it for low mass. In addition, holes were added for further mass reduction. The design met all the supplier and OEM component level specifications. Vehicle testing, however, revealed that the wheel bearing developed high assembled lateral runout (ALRO) and judder. This was due to the tires and wheels being rotated multiple times during a durability schedule. Excessive ALRO will generate high disc thickness variation (DTV) which will lead to pulsation or judder complaints.
The root cause of the vehicle level judder was determined to be caused by excessive ALRO and DTV in the brake corner. The major contributor to this LRO issue was plastic deformation of the bearing wheel flange that occurred with use and multiple tire/wheel rotations.
This vehicle was validated in multiple regions of the world. Regional differences in vehicle service procedures were observed on the same architecture. Further investigation showed that the regions which performed more wheel rotations and other maintenance observed the vehicle judder, while the other region that did less maintenance did not.
To better understand the effect of bearing wheel flange geometry on ALRO in this condition, a lab evaluation was performed. Multiple wheel flange designs were evaluated, including bearing designs with different wheel flange thicknesses and versions with and without weight saving holes. Additionally, bearings with a hybrid aluminum/steel wheel flange were tested.
