Automotive Transmission Rattle:Root Causes to Innovative Solutions

In recent years, significant improvements in vehicle handling and engine noise reduction, together with the growing use of lighter materials in powertrain components have led to the emergence of a plethora of Noise, Vibration and Harshness (NVH) concerns, establishing them as indicators of vehicle quality with direct impact on sales (J. D. Power & Associates Reviews). The cost to industry of meeting customers' NVH expectations is in the order of tens of millions of Pound, whilst warranty claims may further increase the total cost. Transmission gear rattle is now recognised by manufacturers and customers as the number one target for NVH improvement, following the continuous development of engines with higher cylinder compression ratios.Transmission rattle is the result of repetitive impacts between lubricated surfaces in the presence of backlash at the meshing gear teeth, under various loaded or unloaded conditions. Engine torque fluctuations due to combustion and the inertial forces, together with the dynamic response of the complete system result in vibration of the lightly loaded components in the gearbox, such as the idler gears, synchronizer rings and sliding sleeves. Transmission of vibration from the gear shafts through bearings to the gearbox housing is the principal mechanism, radiating noise to the environment. Current vehicle design trends towards lighter flywheels and lower idling speeds increase the prominence of gear rattle as a major noise source.Lack of understanding of the complex interactions between the drivetrain system and its constituent components and industry's need for timely solutions have resulted in costly palliative methods. The common characteristic of all these quick fixes , late in the design process, has been their application-specific nature. Therefore, these approaches do not follow a root-cause, sustainable system method.The proposed research introduces a holistic, wide-ranging and fundamental numerical and experimental study of the drivetrain system, focusing on the gear rattle root cause identification, with emphasis on the effect of lubricated gear meshing surfaces. The development of virtual prototypes, simulating system behaviour will result in sustainable solutions for attenuation of rattle, assisting car manufacturers in their primary target of reducing time to market. The approach proposed here aims to bring a powerful competitive advantage to the UK automotive industry and its supplier base by following a preventive approach to achieve significant cost-savings.