This paper presents SAC (simplex air cam) drum brake cold judder study having predominant frequency below 30 Hz. The test data was gathered to correlate axle wheel brake vibration to cabin inside vibrations on a heavy commercial vehicle. The vehicle test data consist of downhill speed-up drive at neutral, constant speed uphill drive, downhill speed-down drive via braking at neutral. As a first attempt, the data have been analysed in the respect of wheel rotation speed versus vibration frequencies and orders of excitations. It was found that braking vibration frequencies and orders are the same with the generated vibrations during downhill speed-up drive at neutral and constant speed uphill drive. Geometrical irregularities (thickness variation, run-out, concentricity, imbalance, assembly tolerances) influence was found main inputs on the sensed braking vibration by steering wheel inside the cabin. It was noted that the second order vibration is the more predominant among the others and corresponding 2 impulsive imbalance. As a second attempt, SAC (simplex air cam) drum brake hub and drum assembly total run-out (radially including hub, bearings and bushings), drum imbalance, assembly tolerances effect on the induced braking vibration are evaluated. The acceptable level total hub & drum run-out is defined via vehicle level testing to avoid future vibration issues coming from production tolerances.

Ekingen, Onur; Akça, Dilek; - Ford Otosan Product Development Center Guney, Ahmet; - Istanbul Technical University