# Identification and Optimization Study of Cavitation in High Power Torque Converter
## 6 Discussion  
This paper presents a study on the phenomenon of cavitation in high-power hydraulic torque converters. Firstly, a transient flow field model of the torque converter was established. Then, CFD simulation analysis and experimental research were conducted on the torque converter. Finally, a cavitation identification method based on the difference between the flow rate of the inlet and outlet of the torque converter was proposed. The analysis focused on the transient flow process within the torque converter. It was found that the angle between the stator's inlet and the turbine's outlet is a crucial factor in the occurrence of cavitation. An optimized design was then implemented. The angle of incidence deviation of flow injection, \(\Delta\beta_{Dif}\), is formed by the liquid flow angle out of the turbine and the inlet angle of the stator nose during stall conditions. This angle is larger, resulting in more high-speed liquid flow skimming over the nose of the stator and onto the suction surface. This creates a localized negative pressure zone above the front suction surface at the peak position of the stator nose and the stator bending, respectively. This is the main reason for cavitation occurring in the hydrodynamic torque converter. The occurrence of cavitation in the torque converter can be determined by the difference in inlet/outlet flow (\(\Delta L\)). In the case of this torque converter, cavitation can be identified when the \(\Delta L\leq 0\) L/min. Cavitation mainly occurs in the torque converter at high pump input speeds and under large load conditions with low speed ratios. At lower pump input speeds, even with lower speed ratios, cavitation is less likely to occur. In the low speed ratio region (0-0.5) under high pump input speed conditions, cavitation occurs in the torque converter and tends to be strengthened with decreasing speed ratios. Cavitation mainly affects the capacity of the torque converter, specifically the \(M_{bg}\), and has less impact on the torque ratio and efficiency of the converter. The \(M_{bg0}\) of the pump wheel at 1000 r/min is 978.5 N\(\cdot\)m, while that of the pump wheel at 1700 r/min is 735.6 N\(\cdot\)m, resulting in a 33% difference in \(M_{bg0}\). It is important to note that this difference rate of \(M_{bg0}\) reaches 33%. A series of stator optimization design schemes were developed by changing the \(\Delta\beta_{Dif}\) of the torque converter. The aim was to identify the variation rules of \(TR\), \(P_{lowest\_D}\), \(M_{bg}\), and \(\Delta\beta_{Dif}\). It was found that Scheme 2 optimizes the \(P_{lowest\_D}\) significantly while keeping the performance of the zero-speed startup condition basically unchanged. The optimized Scheme 2 has maximum difference rates of \(TR\), \(M_{bg}\), and \(\eta\) controlled within 8%, while maintaining the same external characteristics as the original scheme. Tests were conducted on the stator of Scheme 2 using 3D rapid printing and mounting. The new hydraulic torque converter scheme showed a slight decrease in the overall \(TR\) compared to the original design, with a maximum difference rate of 2.31%. The \(\eta_{max}\) was also generally decreased, with a maximum decrease of 0.9 percentage points. However, this maintained the consistency of the torque converter's \(TR\) and \(\eta\). The hydrodynamic torque converter's \(M_{bg0}\) was significantly improved from 735.6 N\(\cdot\)m to 946.8 N\(\cdot\)m, resulting in a 28.7% improvement rate. Additionally, the cavitation region shrunk from 0-0.5 to 0-0.15, resulting in a significant improvement in the torque converter's cavitation phenomenon. The paper proposes an optimization method for cavitation in torque converters, which can also be applied to optimize the design of other high-power torque converters with similar working conditions. This method provides a new design idea for high-power torque converters to reduce transmission loss and improve reliability.