| Large hydraulic excavators are a kind of engineering equipment widely used in a variety of large open pit mining and large infrastructure projects. However, the development of large hydraulic excavators at home is relatively backward, and there is a big gap in comparison with that abroad. To be more specific, the development of large hydraulic excavators at home is still in the initial stage, with only a few manufacturers capable of producing above100t hydraulic excavators. But the hydraulic excavator machine weight has reached more than1000t in foreign countries at present. Funded by the Shanxi provincial key project of science and technology named "research on energy-saving mechanism and energy efficiency of extra-large mining hydraulic excavators"(20100321025-02), we have studied in this paper the present largest hydraulic excavator in our country with its installation capacity as270t, which will exert a significant effect on the further development of larger hydraulic excavators.During the course of designing the270t large hydraulic excavator, its digging resistance was analyzed and calculated and its mathematic model was established so as to figure out the correct hydraulic control plan and to choose the proper system control parameters. Through the established mathematic model, the horizontal sliding conditions of the hydraulic excavator were analyzed and calculated, and the digging forces of excavator arm and bucket digging conditions were also analyzed respectively. And by the aid of ADAMS and AMESim, the joint simulation of mechanical electrical and hydraulic integration was achieved in the working process of the hydraulic excavator, and the working pressure, power consumption, speed and other parameters of the excavator boom, the arm, the bucket and the clap hydraulic cylinder were simulated. In brief, the analyses, calculations and computer simulations of the related parameters in the working process of the hydraulic excavator have provided a theoretical basis for the development of270t hydraulic excavators.In the excavator hydraulic control system, several pumps were applied to supply oil. In order to distribute flow reasonably and to improve the working efficiency of the excavator, the boom, the hydraulic actuator of the arm, the bucket, the clap and walking devices were equipped with four main working pumps altogether to supply oil, with each main working pump controlling the hydraulic actuator via a set of multi-way valves. Then through the confluence outside valves, these actuators became capable of operating single and compound actions at the speed required.Aiming at excessive energy consumption and high calorific value in the working process of the large hydraulic excavator, variable pumps and proportional multi-way valves were combined to control the speed of hydraulic actuators in the hydraulic control system, and the flow matching between variable pumps and multi-way valves came true through the positive control. At the same time, the main working pumps realized the variable power control in the hydraulic system, thus adapting to different working conditions of excavators. Moreover, in order to reduce the use-cost, the hydraulic control system of the270t hydraulic excavator used electricity as a power source, with hydraulic pump groups driven by AC motors.Regarding that heavy mechanical component weight and large inertia of large hydraulic excavators lead to large pressure impact in the end stage, slow descent speed, low efficiency and poor operability when the boom and the arm drop, proportional regeneration valves were used to achieve energy recovery through flow regeneration circuit, to reduce pressure impact, to accelerate descent speed and to increase operability. In the meantime, working efficiency of the hydraulic excavator was improved with an energy-saving effect, since no hydraulic pumps were applied to supply oil in the descent process. Also, conditions for the arm to drop through flow regeneration circuit were analyzed.In the manufacturing factory and the open pit mine site where the hydraulic excavator was used, the hydraulic excavator was studied, its working performance was verified, the pressure variations of its boom, arm, bucket and clap hydraulic cylinder were tested in both single and compound actions, and the pressure variations and the corresponding time committed were also tested when the main control valve circuit and the flow regeneration circuit were applied respectively in the descent process of the boom and arm. The results show that the designed hydraulic control system can completely satisfy the pressure and speed requirements when the boom, the arm, the bucket and clap operate the loading action with the maximum test load as25t. Besides, descent speed becomes remarkably faster, pressure is more stable, and no significant hydraulic impact exists when flow regeneration circuit is applied in the descent process of the boom and the arm. All in all, through this study, excavator hydraulic control plan has been verified and valuable data and experiences have been secured to further design and manufacture larger hydraulic excavator at home in the future. |
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