The closed circuit hydraulic system is a typical nonlinear and time-varying system. In order to get excellent startup performance, the controller based on expert control method was designed. The theoretical and experimental research of the controller was carried out. Firstly, the working principle of the closed circuit hydraulic system was introduced. The difficulties of pressure pre-balanced control and closed-loop speed control for the system starting were indicated because of its friction, high-inertia and time delay. The influence of nonlinear friction on the startup performance of the system was analyzed. And the initial model of the friction was established through experiments. Then, the intelligent controller was designed basing on expert control method. The startup performance was evaluated by the integral of difference between the desired and the practical speed while the system ran. The static friction model and the parameters of the controller can be modified by the expert controller according to the last two results. Finally, experiments were carried out under different work conditions, namely variable loads and oil-temperatures. The results show that the startup performance of the system is excellent. The robustness of the expert controller is strong under different work conditions. That is, the proposed method is robust in the presence of nonlinearities and uncertainties.

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