Sound Pressure Level Control Methods for Electric Vehicle Active Sound Design

In recent years, active sound design (ASD) has become one of the most important research topics in the field of active sound control technology. For electric vehicles (EVs), road noise and wind noise become the dominant contributors to the interior noise level due to the elimination of internal combustion engines (ICEs). In this case, different vehicle brands tend to resemble each other in the perspective of the interior sound quality, leading to the loss of the distinctive interior sound characteristics and brand image. In order to restore the brand DNA characteristics, ASD is a viable and implementable choice to break the dilemma the next-generation EVs would confront. Sound amplitude control strategy plays a key role in drivers’ subjective perception during dynamically operating an EV equipped with an ASD system. However, it is a new challenge to formulate a reasonable sound control strategy for an ASD system under the circumstance that people have already been accustomed to the variation rule of the engine order sound from the ICEs for decades. In this article, the generation mechanism and “Source-Path-Receiver” model for the interior engine sound of internal combustion engine vehicles (ICEVs) are analyzed based on the transfer path analysis (TPA) method in terms of the airborne and structure-borne transfer paths. Two methods of interior engine order component extraction are investigated and compared. Furthermore, the dynamic characteristics of ICEVs are studied based on the vehicle acceleration and engine output power under accelerating conditions with different acceleration pedal positions (APPs) in order to analyze the correlation between the sound pressure level (SPL) and engine power, which could establish the relationship between the SPL gain of the interior engine order sound and engine power load ratio (EPLR). For an A-class electric sport utility vehicle (SUV), the motor power which could represent the dynamic characteristics of EVs is examined under the accelerating conditions with different APPs. In consequence, an SPL gain control strategy versus APP for an ASD system is proposed on the basis of ICEVs’ SPL gain of the interior engine order sound. An ASD system is then configured based on its controller and the loudspeakers used by the vehicle’s audio system. The control accuracy of the SPL gain is validated using the high-fidelity (Hi-Fi) loudspeakers in the vehicle’s audio system. In summary, this work analytically investigates the variation rule of an ICEV’s interior engine order sound and its dynamic feature, which lays a solid foundation for the control strategy formulation of an EV’s ASD system.