# Identification and Optimization Study of Cavitation in High Power Torque Converter
## 3 Identification of Cavitation in Torque Converter
### Test Bench Setup and Test Procedure  
The torque converter test bench mainly consists of a drive motor, a load motor, a hydraulic system, a heat exchanger system, a control unit and a detection unit. The torque converter is mounted on the test bench as shown in Figure 3. The detailed parameters of the test bench are shown in Table 4.  
During the constant speed test of the torque converter, the pump speed was maintained at a constant 1000 r/min or 1700 r/min, while the turbine speed was varied according to a specific speed ratio [20]. The stall test, on the other hand, was conducted by keeping the  
Figure 3: Torque converter test bench. \begin{table}
\begin{tabular}{c c} \hline
**Item** & **Parameter** \\ \hline Other terms spatial discretization & Second-order upwind \\ \hline Pump rotational speed & 1700 r/min \\ \hline Turbine rotational speed & 0–1700 r/min \\ \hline Stator rotational speed & 0 r/min \\ \hline \end{tabular}
\end{table} 
Table 3: _Cont._  
As shown in Figure 4, the \(TRs\) for input speeds of 1000 r/min and 1700 r/min in the coupled speed ratio region (0-0.8) are nearly identical, with relatively small errors. The distinction between the test \(TR\) and the simulated \(TR\) is primarily evident in the low speed ratio range of 0-0.2. The most significant difference occurs at a speed ratio of 0.1, with a difference rate of 1.9% for the \(TR\). Overall, the difference rate is relatively small. The maximum efficiency \(\eta_{max}\) at 1000 r/min input speed is slightly decreased by 1.1% compared to the \(\eta_{max}\) at 1700 r/min input speed, which is 1.8% different from the simulated \(\eta_{max}\), and the overall rate of difference is small, proving the accuracy of the simulation model. The significant discrepancy in both \(TR\) and \(\eta\) beyond the 0.8 speed ratio is attributed to the rotation of the stator freewheel after the coupling point during the actual test, which enhances the transmission efficiency. As shown in Figure 5, the \(M_{bg}\) tested at 1000 r/min pump input speed and 1700 r/min pump input speed are the same in the high speed ratio region of 0.5-0.9, with a smaller error. In the low speed ratio region of 0.0-0.4, however, there is a significant difference between the \(M_{bg}\) tested at 1000 r/min pump input speed and 1700 r/min pump input speed. This difference rate is inversely proportional to the \(SR\), meaning that the lower the \(SR\), the larger the difference rate. The \(M_{bg0}\) at 1000 r/min input speed is 978.5 N\(\cdot\)m, while that of the pump at 1700 r/min input speed is 735.6 N\(\cdot\)m. The difference rate of the nominal torque reaches 33%. This phenomenon is caused by the cavitation of the torque converter in conditions of high rotational speed, high load, and low speed ratio, as well as a decrease in the torque of the pump and turbine. Figure 5 shows the change curve of \(\Delta L\). It is observed that the \(\Delta L\) decreases as the \(SR\) decreases. In the high speed ratio region, cavitation inside the torque converter occurs less frequently or not at all. The circulating fluid enters the torque converter and exits after a certain leakage, resulting in a larger inlet flow rate than the outlet flow rate, and a positive value for the \(\Delta L\). As the speed ratio decreases and cavitation occurs, a large number of bubbles flow out with the circulating circle, resulting in an increase in the outlet flow. This leads to a decrease in the \(\Delta L\) or even a negative flow difference. At a pump speed of 1000 r/min and a speed ratio of 0.9, the \(\Delta L\) is 1.8 L/min, with a stall condition of \(-0.2\) L/min. At a pump speed of 1700 r/min and a speed ratio of 0.9, the \(\Delta L\) is 0.9 L/min, with a stall condition of \(-2.1\) L/min. The phenomenon of cavitation becomes more pronounced as the \(SR\) decreases and the pump speed increases. Figure 5: Comparison of \(M_{bg}\) and \(\Delta L\). Figure 6 shows the results of the stall test performed at different pump speeds.