Innovative Exhaust System Component that Attenuates Standing Waves with Minimized or Eliminated Leakage 2022-01-5104

Passenger cars with internal combustion engines traditionally use exhaust systems with resonators and mufflers to provide combustion tailpipe orifice noise attenuation. Those elements require acoustic volume which puts constraints on vehicle package space and adds weight to the exhaust system and vehicle. Passive and active valves are also used in the exhaust systems to attenuate noise, helping to reduce muffler volume and reduce other noises like cooldown noise or other noise, vibration, and harshness (NVH) issues that must be dealt with. To attenuate tailpipe noise, we can also reduce the amplitude of standing waves in long uninterrupted pipes of exhaust systems with specifically designed openings to the external environment which does not require a significant increase in weight and vehicle package space. Standing wave management (SWM) is providing such openings and its placement is driven by standing wave physical properties such as wavelength. The theory of using SWM is that open area attenuates noise due to the reduction of standing wave amplitude, and the open area amount required depends on the acoustic targets. Proper placement determines overall effectiveness. One of the primary issues with making openings in the exhaust system pipe is gas emissions below the vehicle and the risk of carbon monoxide (CO) intrusion into the passenger cabin. SWM can also be used with an additional component called an idle pulsation cover (IPC) to reduce leakage/emissions to the ambient. Analysis of the system using tools, such as GT-Power, Ricardo WAVE, and computational fluid dynamics (CFD), help determine the number of required SWM elements, and the leakage risks for the application with or without the use of the IPC. Low engine revolutions per minute (rpm) is where the largest risk for leakage occurs. Emissions testing can help determine the CO intrusion risk, carbon dioxide (CO₂) leak, and IPC effectiveness. IPC effectiveness is determined by volume and the fundamental firing frequency. Consideration of SWM location relative to the cabin can help determine the need for the IPC. Manufacturing techniques for SWM are determined by the application. The use of ribs with optimal location for the holes provides minimal leakage to the ambient. The number of SWM components is also determined by the acoustic targets and available package space. Other similar devices are available but do not directly provide a unique solution to the leakage issues caused by transient flow.