PSI - Issue 75

Marco Bonato et al. / Procedia Structural Integrity 75 (2025) 719–729 Author name / Structural Integrity Procedia (2025)

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The specifications described in the previous section belong to the type called “generic.” They are often calculated by carmakers from a mixture of acceleration measurements and expressed as an envelope of the signal. They are applied for different exposure durations, typically 75 or 96 hours per axis [1]. Indeed, a PSD is the vibration signal that better reproduces vibration loadings during driving conditions. Compared to sines (swept and fixed) and to pure shock, a PSD permits to excite in its defined spectrum all natural frequencies simultaneously. Note that even though most fatigue loadings come as transient events (therefore providing a narrow band excitation), the response of engine cooling products exhibits a broad spectrum, characteristic of a random excitation. On the other hand, components mounted on the engine of the combustion powered vehicles undergoing stress loads which are more sinusoidal in nature, being subject to the typical vibrations generated from a rotating machine. In recent years, the evolution of the market for electric vehicles has resulted in an increasing number of vehicles being powered by batteries (BEV, battery electric vehicles) and hybrid electric vehicles. Components mounted in the premises of the electric motor are subject to both sinusoidal loads but also to the random vibration transmitted by the body of the car. A reliability vibration specification should, in this case, account for both the different types of loads. In practice, the signal is provided as a random PSD, with the road vibration showing high vibration intensity in the low frequency range (5 to 80 Hz) and the vibration generated from the electric motor appearing in the high frequency range (> 100 Hz). 1.2. The Electric Driven Compressor (eDC) The Electrical Driven Compressor (eDC) enables high performance thermal management of A/C and H/P systems, in electric and hybrid vehicles. Designed and validated for efficient cabin and battery, cooling and heating, from a thermal management perspective, the eDC is the beating heart of modern battery electric vehicles (BEV). The eDC is usually mounted in the body of the car (the chassis) but also nearby the electric motor of hybrid vehicles. 1.3. The eDC Inverter Design Validation The role of the inverter is to tune the variable frequency drive – also known as inverter drive – to slow down or speed up the motor that rotates the compressor. This method varies refrigerant flow by actually changing the speed of the compressor. The turndown ratio depends on the system configuration and manufacturer. An electric compressor inverter regulates the motor speed by modulating the frequency of the alternating current. Unlike traditional compressors that operate at a fixed speed (on/off), an inverter allows continuous speed control based on cooling demand. This results in greater energy savings, reduced noise, and more precise temperature control. The inverter converts the direct current coming from the vehicle battery to the alternate current needed to control the rotational speed of the electric motor. The electrical power delivered by the battery is converted to mechanical power by an inverter and an electrical motor. The inverter is composed of a printed circuit board (PCB) with assembled electronic components An essential part of the inverter is the printed circuit board (PCB), which hosts the electronic component that makes up the inverter circuit[2]. The PCB is the skeleton of the inverter, and assumes great importance not only for the performance (minimization of power losses, energy consumption and noise) but also from a durability point of view. The PCB delivers both electrical and mechanical functions during the functioning of the eDC. From a mechanical point of view, the PCB guarantees the structural integrity of the assembly and ensures the robustness of the system. A well designed PCB is expected to withstand the typical stress environment at which automotive components are exposed (thermal and vibration loads). 1.3. The Inverter Flyback The transformer flyback mounted on top of the PCB is a hardware element as depicted in figure 2a. The flyback is situated in the PCB assembly's concentrated routing zone, which is indicated in green as shown in figure 2b. The pin and core make up the flyback component, which is where the solder welds hold the pin to the PCB. Usually surface mounted, flyback devices have a gapped core and a linked inductor. Every cycle, when the input voltage is applied to the primary winding, energy is stored in the gap of the core. It is then transferred to the secondary winding to provide