**2. Construction of HMCVT Shift Hydraulic System Test Platform**

The structure of the test platform of the HMCVT shift hydraulic system is shown in Figure 1. In the hydraulic oil circuit system, the external motor, 1, drives the oil pump, 2, to supply oil to the system, and the overflow valve, 4, adjusts the pressure of the oil circuit into the clutch; the five electromagnetic directional valves, 8, are all installed on the integrated valve plate, 9, to control the pressure oil of the wet clutch to be turned on or off to realize the shifting operation; the oil flow of the clutch is controlled and regulated by the flow speed regulating valve, 7; at the same time, in order to detect the oil pressure fluctuations that occur during the engagement and disengagement of each clutch, a pressure sensor, 6, is installed in each clutch oil circuit; the flow sensor, 5, installed in the main oil passage is used to detect changes in hydraulic oil. Table 1 shows the relevant parameters of the main components in the clutch oil circuit control system. The HMCVT overall bench test system is shown in Figure 2. To increase the objectivity and comparability of the data calculation, when calculating statistics, the starting point is the first sampling point after the controller sends the segment change command, and the end point is the sampling point with a time of 1 s from the start point. That is, the length of the data set is measured in time and the scale is 1 s.

**Table 1.** Main components of the test bench for the shift hydraulic system.


**Figure 1.** HMCVT shift hydraulic control system. 1. Motor. 2. Oil pump. 3. Check valve. 4. Relief valve. 5. Flow sensors. 6. Pressure sensor. 7. Control valve. 8. Electromagnetic valve. 9. Integrated valve plate.

**Figure 2.** HMCVT overall test bench. 1. Diesel engines. 2. Front speed torque meter. 3. Transmission. 4. Hydraulic fixed motor. 5. Hydraulic variable pump. 6. Rear speed torque meter. 7. Loader. 8. Measurement and control platform. 9. Shift hydraulic control system.
