Unique Approach of Modern Automotive Exhaust System Mountings Design for NVH Improvement

Abstract

Minimizing vibration transmitted from the exhaust system to the vehicle’s passenger compartment is the primary goal of this article. With the introduction of regulatory norms on NVH behavior and emissions targets, it has become necessary to address these issues scientifically. Stringent emissions regulations increased the complexity of the exhaust system resulting in increased size and weight. Exhaust system vibration attenuation is essential not only from the vehicle NVH aspects but also for the optimized functionality of the subsystems installed on it. Based on earlier studies, this work adopts a more thorough strategy to reduce vehicle vibration caused by the exhaust system by adjusting it to actual operating conditions. To achieve this, a complete vehicle model of 22 DOF is considered, which consists of a powertrain, exhaust system, chassis frame, and suspension system. A method for evaluating static and dynamic vibration response is proposed. Through the use of the vehicle’s rigid body modes and actual field events, design indicators are carefully analyzed and validated. Based on actual operating conditions, the two main load cases that are taken into consideration are idling and the sweet spot operating zone. To define the sweet spot zone of the dominant vehicle/engine-operating scenario, the vehicle duty cycle is monitored experimentally. The baseline 22 DOF model results show a degradation in exhaust vibration performance in both load cases as its yaw and bounce modes are falling into the resonance region of the idle and sweet spot operating zone load cases, respectively. The acceleration reduction of nearly 10–20 dB in static events, and nearly 10 dB in dynamic events can be evident in the proposed model. The proposed system’s outcomes demonstrate an improvement in the eigenvalues of the yaw and bounce modes, which in turn enhances the vehicle’s overall NVH performance in both static and dynamic load cases. Thus, the study suggests that designers should consider the real field events’ load cases for modern exhaust system-mounting optimization to achieve improvement in NVH behavior, fuel efficiency, emissions performance, and durability aspects of the vehicle.