Conference Agenda

In the course of the electrification of vehicle drives, the requirements for thermal management systems are currently being redefined completely. This has a significant impact on the operating envelope of the compressor as the most important component in it. In addition to standard AC operation, large cooling capacities and mass flows at high evaporation temperatures are needed for fast charging, while heat pump mode is characterized by low suction pressures and high pressure ratios. These new tasks significantly increase the required stable pressure and speed ranges of scroll compressors, which are de facto standard in most electrified mobile applications. A particularly complex engineering task and potentially major time bottleneck is tuning a variable back-pressure system, which most modern scroll compressors rely on for axial compliance between fixed and orbiting scroll. Natural refrigerants, especially the transcritical use of R744, for example, require an even more precise back-pressure tuning than usual. As we will show, ultra-fast exact analytical geometry calculations and 1D thermodynamic flow simulations are combined in a software tool that performs a fully automated optimization process to solve the task of ensuring proper back pressure over the entire operating envelope of the scroll compressor. To have such an efficient and lean simulation toolchain is the key to being able to react in an environment of ever-changing boundary conditions and allow for rapid development and investigation of new machine concepts and variants.

Scroll compressors were widely employed in electric vehicles due to their high efficiency, low noise, and low vibration. The electric scroll compressor is operated through direct motor drive, with motor cooling facilitated by the intake refrigerant. After compression, the refrigerants were exhausted through the oil and gas separation structure. However, substantial pressure loss occurs due to the larger intake and exhaust flow areas compared to the scroll area. This paper presents a complete computational fluid dynamics (CFD) model of the electric scroll compressor. The model incorporates domains for the motor, the rotating main balance weight, the crescent-shaped scroll compression chambers, as well as the exhaust buffer chamber and oil separator. Through calculations, the pressure and temperature distribution within the scroll compressor are determined. Under specified operating conditions, as the rotational speed escalates from 5000 rpm to 10000 rpm, the inlet pressure loss experiences an increment from 5-15 kPa to 25-55 kPa. Concurrently, the exhaust fluctuation transitions from 15-15.9 bar to 16-17.8 bar. Comparatively, the simplified model exhibits significantly enhanced volumetric efficiency and isentropic efficiency. When simplifying the model and establishing boundaries, the pressure loss should be considered on the operating conditions to enhance calculation accuracy. The developed complete CFD model serves as a valuable tool for analyzing and enhancing the performance of electric scroll compressors.

Integrated thermal management of electric vehicles (EVs) require advanced cycle configurations that can effectively condition battery pack, power electronics, and cabin under different ambient conditions. Heat pumps play an important role and the design of high capacity and efficiency compressors that can meet the transient thermal loads is crucial. In this study, a generalized analytical modeling approach of symmetric variable wall-thickness scroll configuration is proposed to investigate the potential benefits variable-geometry scroll wraps. The analytical approach considers different fundamental scroll wrap curves (e.g., circle involute, circle arc, ellipse segment, line segment) as well as other parametric-function-defined curves to determine analytic solutions of chamber volumes, areas, line contacts and flow paths. A case study is conducted to demonstrate the accuracy and capabilities of the modeling approach. Specifically, an R-1234yf scroll compressor has been analyzed with the aim to quantifying losses and identifying design trade-offs. Furthermore, a vibration-based reed valve model is also included in the model to assess its impact on the compressor operation. As a result of the modeling efforts, both thermodynamic and mechanical investigations have been conducted to optimize the design space of variable wrap-geometry scroll compressors.

The air conditioning system in the TMS of EVs has high energy consumption, which seriously impacts the cruising range of EVs, and this part of the energy consumption mainly comes from the scroll compressor.

The development trend of the EV scroll compressor is towards miniaturization, which results in the compressor often having a shorter scroll wrap and possibly needing to operate at speeds up to nearly 10000 rpm. Furthermore, the smaller built-in volume ratio may cause discharge delay under typical operating conditions. The scroll plate features, including the lengths of the scroll wraps, the shape and position of the ports, and the crescent groove at the beginning of the orbiting scroll, make the fluid flow within the scroll chambers complicated, resulting in the thermodynamic process becoming significantly asymmetric.

To study the asymmetric thermodynamic process of the EV scroll compressor under different operating conditions and speeds, this paper established a corresponding mathematical model of the compressor, which mainly includes the geometry analysis model, the thermodynamic process model considering the bypass flow process, and the valve dynamics model coupled with the former. The thermodynamic process of the scroll compressor was calculated and analyzed. The asymmetric compression characteristics under different working conditions and speeds were revealed.