Research On Key Techniques Of Independent Metering Directional Valve Control System

Hydraulic system is well used in mobile machinery, multi-way directional valve is the key component in hydraulic system of mobile machinery, its properties has high relationship to the operational and energy saving characteristic of mobile machinery. Meter in and meter out orifice of traditional multi-way directional control valve is controlled by a single main spool, but meter in and meter out orifice in independent metering valve is separately controlled by two spools, so control degrees of freedom in independent valve control system is increased, which makes it possible to further improve operational and energy saving characteristic of mobile machinery. Controller design for velocity and pressure control of independent system as well as application of independent valve control system in mobile machinery, which has been considered as a challenge up to now, is responsible to improving system performance. Therefore it is necessary to study control strategies of independent metering valve control system and the mechanical-hydraulic coupling characteristic of mobile machinery, make full use of the increased degree of freedom to enhance operational and energy saving performance of mobile machinery.In this thesis, a new velocity control method to control the open center load sensing independent metering valve control system has been proposed, pressure difference of velocity control direction valve is regulated according to operator input command velocity, which is not set at a fixed value as in traditional load sensing system. When the command velocity is low, pressure difference is reduced, which reduces the velocity control gain, improve stability and energy saving performance; when the command velocity is high, pressure difference is increased, which increases system velocity control gain and enhances velocity dynamic response, this method was implemented in a variable command velocity lift experiment, obtained results showed that above 8% of energy saving performance was achieved using proposed method. Work modes of excavator actuators have been studied, a work mode selection criterion has been proposed, high pressure regeneration extraction mode is more suitable to control the downward motion of boom than low pressure regeneration extraction mode, experiment showed that high pressure regeneration extraction mode reduced 20% overshoot of velocity; in boom and arm simultaneous motion condition, it suggests that boom uses power extension work mode, arm uses high side regeneration extension work mode, it improved 7% efficient than both using power extension work mode. An independent metering valve control multi-actuator system with a counterbalance has been studied, a variable gain velocity control method has been proposed to improve system stability, experiment showed that the proposed method reduced 40% overshoot of velocity coMPared with using the fixed gain velocity control method. All obtain results provided the theoretical basis and application examples to explore independent metering valve control system.to improve operational and energy saving performance of mobile machinery.In chapter 1, the aim and significance of the study in the thesis were discussed. The current research progresses on IM technique were reviewed. The main research subjects were presented. In chapter 2, three different controllers were proposed to control IM valve control system based on the built mathematic model, the performance of those controllers were coMPared through simulation and experiment, Lyapunov based adaptive robust controller obtained highest velocity control accuracy.In chapter 3, controllers designed for combining IM and LS technique have been developed. A new control method for OCLS-IM system has developed to enhance energy saving performance by varying the pressure differential of IM valve according to the operator input velocity control signal. A CCLS-IM controller which differentiates the level of the external loads to choose work mode for actuators was also developed, it can also improved energy saving performance of the whole system significantly.In chapter 4, multi-actuators simultaneous motion control method of IM valve control system have been studied. CoMParisons of dynamic response of velocity control between traditional proportion directional valve control two-cylinder system and IM valve control two-cylinder system has been carried out. Obtained simulation results showed velocity response of IM valve control system was faster and more stable. A variable gain velocity control method was proposed to stable IM valve control two-cylinder velocity control system with a counterbalance valve.In chapter 5, a 2-ton excavator IM valve control system has been built, velocity control performance of different work modes were experimentally tested.It was found, when the boom was in extraction, high side regeneration extraction mode was preferred to be chosen due to its good velocity control performance. OCLS-IM control strategy was also verified in boom lift velocity control mode. Then arm and boom were controlled to lift and lower simultaneously with the IM technique, good velocity control performance was achieved.In chapter 6, conclusions in this thesis were summarized and future research proposals were suggested.