# Research on Prediction Method of Hydraulic Pump Remaining Useful Life Based on KPCA and JITL
## 4 Life-Cycle Test and Signal Acquisition of Gear Pump
### Life-Cycle Signal Acquisition
Therefore, when the temperature of the hydraulic oil is above 49 \({}^{\circ}\)C, forced-air cooler 4 starts to work to reduce the temperature of the hydraulic oil, and when the temperature of the hydraulic oil is below 30 \({}^{\circ}\)C, forced-air cooler 4 stops working. To ensure the safety of the test, the safety pressure of direct-acting relief valves 10.9-10.12 is set as 30 MPa. To accelerate the performance \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Serial Number** & **Component Name** & **Component Model** & **Component Performance Parameter** \\ \hline
1 & Gear pump & CBWF-304 & Rated pressure: 20 MPa, rated speed: 2500 r/min, theoretical displacement: 4 mL/r \\
2 & Flowmeter & MG015 & Measuring range: 1–40 L/min \\
3 & Pressure sensor & PU5400 & Measuring range: 0–400 bar \\
4 & Torque-speed transducer & CYT-302 & Torque range: 0–20 Nm, speed range: 0–3000 r/min \\
5 & Temperature sensor & CWDZ11 & Measuring range:–50–100 \({}^{\circ}\)C \\
6 & Data acquisition card & NI PXIe-6363 & 16 bits, 2 MS/s \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Models and performance parameters of main components of test bed. Figure 5: Schematic of step-stress acceleration degradation test. degradation state of the gear pumps, in the life-cycle test bed, the step-stress acceleration degradation test method is adopted. This method can effectively reduce the test time and reduce the test cost compared to a constant-stress acceleration degradation test. The hydraulic pumps were considered to be in a failure state when their volumetric efficiency became lower than 70%, following which the test was stopped. The volumetric efficiency changes of pumps 1-4 in the test were analyzed, as shown in Figure 6. When the working time of the pumps exceeded 1050 h, their volumetric efficiencies were lower than 70%; therefore, the test was stopped. Therefore, 1050 sets of original signal data of pumps 1-4 were collected during the test, that is, each of the four gear pumps operated for 1050 h.  
To model and analyze the degradation process of the gear pumps, the following two definitions are used. The first one is the start failure point, P, of the gear pump, the point at which the volumetric efficiency of a gear pump is below the 80% line for the second time or the subsequent volumetric efficiency is completely below the 80% line. The second definition is the full failure point, F, which is the point at which the volumetric efficiency of a gear pump is below the 70% line for the second time or the subsequent volumetric efficiency is completely below the 70% line. From Figure 6, the time points of the start and full failures of each gear pump can be obtained, which are listed in Table 4. Figure 7 shows the following wear of each component of gear pump 1 after 1050 h of operation: gear end-face wear, side plate wear, and pump body wear. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Series Number**} & \multicolumn{2}{c}{**Time of Start**} & \multicolumn{2}{c}{**Time of Full**} \\  & **Failure/h (Point P)** & **Failure/h (Point F)** & **Time of F-P/h** \\ \hline
1 & 699 & 1033 & 334 \\
2 & 698 & 1030 & 332 \\
3 & 496 & 1025 & 529 \\
4 & 565 & 1034 & 469 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Start and full failure times of each gear pump. Figure 6: Volumetric efficiency degradation curves of gear pumps.