Forward design of the hydraulic system for the two-speed electric drive automatic transmission

The two-speed electric drive automatic transmission (2EDAT) is an effective scheme to improve the economy and power performance of electric vehicles. It is significant to carry out forward design, valve body improvement, and oil circuit optimization of the hydraulic system for 2EDAT. In the study, the functional requirement of 2EDAT hydraulic system was firstly analyzed and key parameters were calculated to determine the principle design of the hydraulic system. Then, the simulation model of the hydraulic system was established in the multidisciplinary dynamic simulation platform ITI-SimulationX and the changes in the pressure of the main oil circuit, the clutch oil pressure, and the cooling and lubrication flow in the shift process of the hydraulic system were simulated and analyzed. Furthermore, according to the principle scheme and constraint conditions of the whole machine, the overall layout and the hydraulic valve plate of the hydraulic system were designed and the valve plate and hydraulic system were tested on the bench. The test results of clutch pressure were 5.73%–13.12% lower than the designed value and did not meet the design requirements. Finally, according to test results, the processing defects of the pressure reducing valve were mitigated and the main oil circuit was optimized for another test of the valve plate and the hydraulic system. The test results of clutch pressure were 0.35%–8.60% higher than the designed value and met the design requirements. The results showed that the optimized hydraulic system realized the better control effects on the main oil pressure and clutch oil pressure in the shift process, including the fast and accurate clutch shift response, the sufficient cooling and lubrication flow, and smooth working conditions.