ODS of Fixed Calliper Brake and Double Wishbone Axle During Creep Groan at Corner Test Rig

The NVH quality of automobile friction brake systems is highly important. Self excited creep groan phenomena are critical in that field. The underlying low frequency stick slip of the friction pair occurs for cars with electrified powertrains and/or automated driving features in particular. In order to develop remedial measures, typical creep groan vibration patterns are also of interest. To this end, time discrete ODS analyses have been performed.
A double wishbone axle setup including fixed calliper brake system has been investigated at a vehicle corner test rig. Machine and facility enable reproducible test matrix combinations of brake pressure and drum velocity under defined environmental conditions. The conducted ODS methods rest on two accelerometer allocations. One sensor arrangement was focussed on axle and suspension components, the other one on brake parts. In addition, the disk rotation has been captured in a fine incremental resolution. In order to realise a mechanical sensitivity study, two alternative upper control arm types were tested in terms of creep groan.
A large number of the test matrix combinations give birth to brake creep groan phenomena. The manifested stick slip cycles are within typical fundamental frequency spans below 25 Hz and from 60 to 100 Hz. The upper control arm rubber bushings have an impact on the higher stick slip frequency which shifts approximately 30 Hz here. The lower control arm bushings rather affect the bottom stick slip frequency span instead. Exemplary ODS visualisations reveal specific non linear component movements in dependence of current operational parameters. Thus, influences of local elasticities and/or subsystem resonance effects can be identified and global phases of stick or slip can be deduced.
The study considers sustained creep groan. Triggering events as well as charging periods, which may also be of interest, are not investigated. Furthermore, limited numbers of sensors and data acquisition channels led to two separate arrangements with restricted spatial resolutions. All solid (metal) parts are assumed to interact as rigid bodies with geometric and/or flexible joints. It is noted that stick slip of the friction pair is interpreted in a macroscopic sense here.
A former work shows time discrete ODS orbits at brake module level. The current publication includes also the axle and suspension system. Another creep groan related work treats bushing parameters in simulations. The present paper involves a real world component study instead.
This study treats experimental creep groan investigations at automobile front corner level. The customised ODS analyses reveal underlying mechanisms as well as stimulated feedback resonances in an illustrative way. All visualisations agree with the authors’ subjective hands on perceptions. Eventually, the influence of axle bushing properties is highlighted.