Abstract: In the process of the digital hydraulic pumps/motors displacement shifting, the torque impacts problem which influences the ride performance has always been found. Some researches had been made for torque impact mechanism and its inhibition. According to the experiment results, in the process of digital control there exists a different degree of hysteresis between pressure establish-ment/disestablishment and signal outgoing in different diameters of reversing valves, which causes pressure superposition of multi-stage pump and further leads to the additive effect of impact. In order to solve the above-mentioned problem, on the basis of the re-sponse time for reversing valves and system pressure impact, a step sequence control strategy had been formulated. Then the control strategy had been simulated by using AMESim software, and verified the strategy by way of experiments. Experiment results show that the step sequence control strategy reduces impact degree during the process of displacement shifting by 23%, relieves the sys-tem's torque impact effectively, and satisfies the dynamic continuity principle of the system.

Key words: turn and control of fluid, digital secondary component, torque impact, step sequence control strategy