Investigation of gear rattle phenomena

The acceptance by discerning customers of passenger cars is dependent upon both the actual noise level and the subjective noise character. The subjective noise character itself can contain, among other features, undesirable noise phenomena which become apparent at certain points in the vehicle operating range. One such critical phenomenon is gear rattle, which is mainly present under low speed, high load conditions. Due to changes in the angular velocity of the crankshaft, gear rattle under driving conditions occurs at the unloaded gears and splines. It is influenced by a combination of features, such as the inertia of the flywheel, clutch, and all gears, the transmission drag, and the resonant characteristics of the driveline. The effect on airborne noise is also influenced by the characteristics of the vibration transfer paths from the gear teeth meshes via shafts and bearings to the transmission housing. To analyze the interactions of these parameters, it is necessary to conduct both vehicle tests, either on the road or with a chassis dynamometer, and to investigate the bare engine-transmission unit in an anechoic test cell. The first part of the investigations reported in this article deals with the definition by conventional methods of the noise phenomena in the passenger compartment and a parallel application of a subjective noise character evaluation system. This is followed by a correlation analysis of the noise phenomenon recorded in the passenger compartment with the noise at the source. Finally, a comprehensive investigation of the noise phenomenon on the bare power unit and the potential of key parameters for reduction at the source will be described.