Investigation of Bearing Outer Cup Interference Loss in Wheel End Hub of Commercial Vehicle 2015-01-2730
Ever-increasing operational cost, reducing profit margins & increase in competition, it is of upmost significance for fleet owners & drivers to opt for a vehicle having maximum uptime. OEM's are under immense pressure to design & develop vehicles/subsystems which are reliable enough to minimize downtime & withstand heavy overloading plus extreme operating conditions especially tippers. Vehicle systems like Wheel end (hub, bearing, and grease) which are designed & packaged according to a very stringent envelop & operate as a closed system facing all the extremities of operating conditions. This undoubtly make them prone to no. of failure modes which are resulting in vehicle unplanned stoppages, so any failure mode related to the same must be taken care with utmost importance.
In commercial vehicles the bearing outer cup is in interference fit with the hub. These bearings of wheel hub have to be maintained at the wheel end play of few microns. In one of VECV new range of HD products we had faced the issue of loss of fit of bearing outer cup with hub. As a consequence of loss of fit, premature bearing failures, disturbance in hub endplay & most importantly higher /uneven tire wear observed. This is resulting in customer dissatisfaction due to high downtime & also increases warranty costs.
This paper investigates the effect of various independent factors plus their combined effects on interference loss of hub & bearing with the help of DOE approach. Correlating this phenomenon with design parameter is big challenge as it is occurring in a closed environment i.e. wheel hub. Investigation starts with the study of failed hubs which indicated the localized deformation & removal of material from bearing sitting location. Based on this input factors are identified for performing DOE. Each of these factors is converted into a measurable parameter into design & analysis/experiments are planned accordingly. To minimize the evaluation time it was decided to evaluate effect of some factors virtually. Contact pressure & stress analysis study is done with the help of Ansys CAE tool. Analysis of remaining parameters i.e. hub stiffness, load, temperature posed a bigger challenge as it is not possible to evaluate the combined effect of these in CAE. Rig testing is only other way to evaluate the same in minimum possible time. Due to unavailability of rig in VECV accelerated rig testing validation done with one of our bearing supplier with the duty cycles replicating the actual loading conditions. Failure mode got replicated in rig validation.
Above investigation gives us an insight that phenomenon of creep occurs between wheel housing & bearing outer cup which causes the fit to loose. With respect to part design primarily low part stiffness in the bearing sitting area on wheel hub & secondarily improper fit between hub & bearing outer cup are contributing towards the same.
Based on the findings different combination of fits of bearing cup with hub & different hub stiffness are tried by making physical prototypes & same are tested on vehicle. The best combination of hub stiffness & fit of hub-bearing is adopted in design & no such issue reported till day. This investigation & its findings has helped in reducing product design time and cost by detecting any failures in the early stages of product development lifecycle & reducing design iterations in later stages for all future projects.