中文摘要：

由于二氧化碳制冷系统的制冷效率与人工合成制冷剂相比处于劣势，故采用跨临界循环，并利用膨胀机回收膨胀功以减少膨胀过程的能量损失，达到提高整个循环效率的目的。针对目前膨胀机存在的诸多问题，设计应用于跨临界CO2压缩循环的新型双转子滚动活塞膨胀机。该膨胀机的一级气缸始终与进气管连通，二级气缸始终与排气管相通，随着转子的转动在两气缸之间形成膨胀空间，因此，不需要专门的进气控制装置。对膨胀机的运行过程进行理论分析和设计计算，得出主要结构参数，并进行受力和力矩计算。分析结果表明，在膨胀过程中，一级转子的总力矩始终为正值，膨胀将结束时两转子的总力矩变为负值。在角度θ2之前，二级转子的驱动力矩大于一级转子的驱动力矩，在角度θ2之后，一级转子的驱动力矩更大。

英文摘要：

The efficiency of CO2 refrigeration system is lower than that of traditional refrigeration systems using synthetic refrigerants The expander can reduce energy losses in the expansion process, so the transcritical cycle with expander is adopted in order to improve the COP of the CO2 refrigeration cycle. In view of the current problems in the expander, a new two-rotor rolling piston expander used in transcritical CO2 refrigeration cycle is designed. This expander needs no special suction control equipment, whose first-stage cylinder connects with the suction pipe, and whose second-stage cylinder connects with the exhaust pipe, expansion space is formed between two cylinders. Theoretical analysis and design calculation of expander operation process are carried out to obtain the main structural parameters, and force and moment are calculated. Analytical result shows that the total moment of the first-stage rotor is always of a positive value in the expansion process and the total moment of the two rotors becomes negative when the expansion is about to end. The driving moment of the second-stage rotor is greater than that of the first-stage rotor before θ2, and after that the driving moment of the first stage rotor is greater.