In conventional automotive gearboxes, all gears are engaged, but not all of them are involved in transmitting power to the wheels. These unloaded gear pairs are, nevertheless, subjected to light forces due to slight torque and speed variations and also to the interaction between the tooth surfaces and the lubricant. Under certain circumstances, these conditions can lead to repeated impacts among teeth flanks and counter flanks. As a consequence, undesirable vibrations and noises are produced, which are commonly denominated as rattle phenomena, that result in premature fails and damage of other elements coupled to the transmission, as well as in a lack of passengers comfort. Within this framework, in this study, a survey of the available formulations, which simulate the forces behavior in lubricant environment under rattle conditions, has been performed. In a previous work, the authors assessed different formulations for this purpose, observing significant differences among them and also concluding that two effects should be considered in order to properly model rattle conditions. One is linked with the pressure variation due to the fluid entrance in the tooth conjunction, whilst the other is related to the lubricant squeeze when teeth profiles are approaching. Having this in mind, in this paper, the dynamic behavior of gear transmissions under low-torque conditions were assessed with different hydrodynamic formulations, which consider both squeeze and fluid entrance effects. With this purpose, these nonlinear forces derived from each formulation were obtained and compared for a sample transmission, simulating several working conditions of torque, speed and lubricant viscosity. The results are shown by means of the dynamic transmission error as well as the forces present in the conjunction.
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