Research On Design And Evaluation Method Of Active Sound Generation System For Electric Vehicles

With the emerge of the "Five Trend Era"-"Lightweight,Electrification,Intelligentialization,Networking,Sharing" in today's automobile industry,multi-cylinder engines are gradually replaced by fewer-cylinder engines and electric motors.As a result,it's more difficult to develop a brand engine sound by means of optimizing the mechanical systems including intake and exhaust systems.In order to maintain an inheritance of brand engine sound,and avoid the interior sound's homogeneity during dynamic driving for electric vehicles(EVs),Active Sound Generation(ASG)is one of the most effective solutions.ASG is a complex interdisciplinary subject involving the integration of automobile acoustics,electronic acoustics,musical acoustics,sound signal processing and other disciplines.It focuses on sound synthesis,sound design and active sound control.Therefore,it is indispensable to carry out the research on design and evaluation method for ASG system of EVs.In this paper,an A-class electric SUV is taken as the research object.At first,the development trend of EVs' interior sound is investigated.Then a mathematical model of engine order sound is established.A Short-Time Fourier Transform and Synthesis technology based on Kaiser Window Function is proposed,which could successfully extract and synthesize engine order sound inside cabin.Furthermore,an interior sound design method for the acceleration condition is studied,during which a sound target for ASG system is defined.And a control method for the ASG system is formulated based on the interior noise characteristics due to the engine order sound amplitude variation.The ASG hardware and its main functional circuits are designed,and the control software for the system is developed.Consequently,an ASG system is configured based on the loudspeakers of the electric vehicle's audio system and the frequency response characteristics of the loudspeakers are also tested.By establishing a design process along with a calibration and evaluation method for the ASG system,the acoustic target of the ASG system is validated.This work provides an interior sound design process for EV's accelerating condition,as well as a sound control,calibration and evaluation methodology for ASG systems.Firstly,vehicle NVH characteristics arisen from the EV's architecture is analyzed.The trending analysis of the EVs' sound quality as well as the future market expectation investigation is conducted and its importance is revealed.A questionnaire titled "The Perception of EVs' Interior Sound in the Future" is designed,with 456 surveys being carried out and statistically analyzed.The surveys accentuate the influence of driving experience,age,gender and occupational background,and conclude that customers' demand for interior sound of future electric vehicles is diversified,among which the classical engine sound is still one of the most important concerned factors for electric vehicles' interior sound.Secondly,the spectrum differences of interior sound during acceleration between internal combustion engine vehicles(ICEVs)and EVs are investigated and compared.A mathematical model of the engine order sound is established,and the principle of Short-Time Discrete Fourier Transform and Synthesis is expounded.A Short-Time Fourier Transform and Synthesis technique based on Kaiser Window Function is proposed to successfully extract and synthesize engine order sound components.Ultimately,synthetic accuracy of engine order sound is verified by subjective and objective evaluations and analyses.The result indicates that this proposed method satisfies the accuracy requirement for the synthesized engine order sound of the ASG system.Subsequently,a conceptual design target for EVs' interior sound is formulated.An interior sound design method for acceleration condition is proposed by considering three factors including engine order composition,spectrum energy distribution and amplitude enhancement in typical speed range.The overall level target and selection principle of control parameters for the ASG system are elaborated.Furthermore,an amplitude control method of ASG is defined on the basis of the variation characteristics of engine order sound amplitude in response to the engine output power with regard to ICEVs.Specifically,a control strategy of amplitude gain with acceleration pedal is formulated,with the gain coefficient ? of the sound amplitude found to be 8.5[dB(A)/100%].This leads to a synchronous trending variation between ASG system and EV's dynamic characteristics.Then,the hardware and main circuits of the ASG system are then designed and a principle prototype is fabricated,followed by the functional measurement of the main chips.The results demonstrate that power supply voltage,CAN signal and audio signal of the prototype fulfill the design requirements.Moreover,the ASG control code is developed,and a process composed of modularized control code with the program workflow is established.The CAN information communication between ASG system and the EV is configured and completed.Eventually,an ASG system based on loudspeakers of the audio system on the A-class electric SUV is implemented.The frequency response characteristics of each loudspeaker are tested,and the results satisfy the ASG requirement.Finally,a EVs' ASG design process is established.A sound calibration and evaluation method is proposed by mainly considering frequency response characteristics of loudspeakers,control accuracy of amplitude and psychological acoustic parameters.Consequently,it is verified that the sound synthesis and amplitude control is accurate enough to meet the design requirement,among which the amplitude and gain can be controlled in the error range of 1.4dB(A)and 0.4dB(A)respectively during full acceleration.The influence mechanism of loudspeaker frequency response on the accuracy of sound synthesis and amplitude control is clarified.Correspondingly,it is confirmed that the ASG system could meet the target in terms of sound amplitude and spectrum characteristics realizing a maximum reduction of 1.0 acum in sharpness,which proves that the EV's interior sound quality is optimized.Through subjective evaluation,it is further verified that the ASG system can improve comfort and dynamic interior sound quality for EV under accelerating and cruising driving conditions.