## 4 Motor-Hydraulic Pump Energy Consumption Analysis Experiment
### Experimental Analysis
#### 4.2.2 Selection Basis for the Experimental Parameters  
In conjunction with the load-condition requirements of the excavator boom under investigation, specific working conditions were established. The operating speed of the hydraulic cylinder for the boom was set at 1200 m/s, necessitating a hydraulic pump flow rate of 85 L/min and an operational pressure range between 8 to 14 MPa. To enhance experimental efficiency within the specified load-condition parameters, the hydraulic pump's working flow was maintained at 85 L/min while varying the working pressure to values of 8, 10, 12, and 14 MPa respectively. Special load conditions were defined to analyze through experimentation the correlation between optimal speed and load power. As indicated by the theoretical analysis in Section 3.2, when both the displacement of the hydraulic pump is minimal and the motor speed is excessively low, there exists a reduction in operational efficiency for both the motor and the hydraulic pump systems. Therefore, since the experiments were aimed at improving overall efficiency, a setting range for speeds from 1200 to 1800 was adopted alongside a displacement range from 70.8 mL/R to 47.2 mL/R, thus establishing a displacement ratio range of approximately \(-0.5\) to \(-0.85\). Based on the operational requirements of the boom, the motor speed range is established between 1200 and 1800 r/min, utilizing a speed regulation interval of 25 r/min to increase the motor speed while concurrently reducing the hydraulic pump displacement incrementally. The outlet flow of the hydraulic pump is maintained at a predetermined value of \(Q=85\) L/min. Pressure and flow data are monitored via the outlet pressure and flow sensors associated with the hydraulic pump. As illustrated in Figure 7a, under conditions where the hydraulic pump pressure \(p=8\) MPa and the working-flow demand \(Q=85\) L/min, it is observed that as motor speed increases under this load condition, the displacement decreases; consequently, the energy conversion efficiency between the motor and the hydraulic pump initially rises before subsequently declining. At a motor speed of \(n=1325\) r/min with a hydraulic pump displacement ratio \(i=0.852\), both components can operate within their high-efficiency zones, achieving an energy conversion efficiency of up to 61.05%. As illustrated in Figure 7b, the motor efficiency increases first and then decreases with the increase in speed, and the hydraulic pump efficiency gradually declines with the speed growth; that is, the efficiency space \(\Delta\eta=19.8\%\) can be improved within the whole speed range. As illustrated in Figure 8a, under a hydraulic pump pressure of \(p=10\) MPa and a working-flow demand of \(Q=85\) L/min, it is observed that with increasing speed, the displacement decreases under this load condition. Furthermore, the energy conversion efficiency of the motor-hydraulic pump initially increases before subsequently decreasing. When the motor speed reaches \(n=1375\) r/min, and the hydraulic pump displacement ratio  
Figure 7: (**a**) Efficiency curves for \(P=8\) MPa, \(Q=85\) L/min. (**b**) Efficiency changes under different combinations of speed and displacement. is \(i=0.727\), the motor and the hydraulic pump can operate within their high-efficiency zones, achieving an energy conversion efficiency of up to 68.12%. As illustrated in Figure 8b, the efficiency of the hydraulic pump increases first and then decreases; that is, the efficiency space \(\Delta\eta=20.9\%\) can be improved in the speed range. As illustrated in Figure 9a, under a hydraulic pump pressure of \(p=12\) MPa and a working-flow demand of \(Q=85\) L/min, the displacement decreases as the speed increases under this load condition. Furthermore, the motor-hydraulic pump's energy conversion efficiency initially rises before declining.