Study on Load Spectrum Extraction Method of Battery Pack Fixture Point in Frequency Domain

Abstract

A method to obtain load spectrum of battery pack fixture point in frequency domain is proposed. The multi-body dynamics model of the vehicle is established, and virtual iteration is carried out with the road load spectrum collected on the proving ground test as the target signal, and the random load spectrum of the connection points between suspension system and body is obtained. The time domain signals of the connection points are converted into frequency domain signals, and random response analysis is carried out to obtain the acceleration PSD matrices of the body monitoring points and the battery pack fixture points. The PSD of monitoring point calculated by the frequency domain method is compared with the measured signal PSD. The results show that the calculated values are in good agreement with the measured values, therefore, this method is very effective to some extent. The proposed load spectrum extraction method in frequency domain also has reference value for the fatigue load spectrum extraction of other connecting parts of vehicle body. Introduction The vehicle is subjected to the random loads from road surface during driving because of the unevenness of the pavement [1]. In recent years, the electric vehicles are developing rapidly. As battery pack is the most important part of the energy supply system of electric vehicle, its fatigue performance under complex random loads affects the safety of the vehicle a lot. Therefore, the acquisition of the fatigue load spectrum of battery pack fixture point has important engineering significance. For the performance requirements of battery pack structure under random vibration, there are GB/T 31467.3-2015, SAE J2380 and other standards at home and abroad. Based on the SAE J2380 standard, Wang Wenwei et al. carried out fatigue analysis on the battery pack with the use of standard load spectrum [2]. However, the fatigue characteristics of the battery pack structure in real working condition cannot be obtained by the standard vibration test. At present, there are few studies on the fatigue characteristics of the battery pack under real road excitation, and most of them are carried out in time domain. Chen Qi obtained the driving force and driving displacement of battery pack through virtual iteration based on the measured load spectrum of the battery pack in urban road conditions, which were used as the excitation to the fatigue simulation [3]. The random load test can simulate the actual random load accurately. Power spectral density function is the basis for loading the random load test. Therefore, the acquisition of the frequency domain load spectrum of battery pack fixture point is significant. Youngwoo Choi et al. proposed a uniaxial vibration fatigue test method with weighted power spectral density as excitation, which proved that the method can reflect the real road conditions well and shorten the fatigue test cycle [4]. Based on the six-component force signals of the wheel spindle centers, Bishop et al. performed a random response analysis on the finite element truck model to obtain the frequency domain load spectrum of the spare wheel bracket and verified its effectiveness [5]. However, there are few studies on the methods of extracting the load spectrum of battery pack fixture point in frequency domain at home and abroad.