| Currently, energy saving has become one of the most important world problems because of the energy crisis and the resulting increase of fuel cost. Only 30% of the hydraulic system input power is utilized in a conventional type excavator. Many proposals for energy saving in oil hydraulic systems had been discussed. One of the most important research directions of improving hydraulic system efficiency is to reutilize the gravity potential energy and kinetic energy.The hydraulic excavator's massive work device, when lowered, generates a great deal of force on the rod end of the boom cylinder. In turn, this exerts huge forces on the fluid and blind end of the cylinders. Fluid forced from the boom cylinder at several ten bars, in most instances, throttles through valves and returns to the reservoir. The result:potential of energy is lost as heat when the boom lowers. Also, a large amount of energy is wasted during lowering of stick and bucket and braking of upper structure. To resolve this problem, it is necessary to reutilize the potential energy and kinetic energy.The main contents are briefly introduced as following:Base on the distribution of recoverable energy in 7-ton and 20-ton excavator hydraulic system, multi-body dynamics, hydraulic system and system energy loss model is developed; the potential recoverable energy during the typical working cycle is calculated. Then the boom fast down and up experiment of 7-ton excavator and typical working cycle experiment of 20-ton excavator are carried out. After analysis, the results present the amount of the recoverable energy distributions and find the way to improve the efficiency of the hydraulic system.The inefficiency of the traditional boom system is analyzed. And hydraulic energy recovery is compared with electrical energy recovery system. According to the separate meter-in meter-out, flow regeneration and hydraulic energy recovery technology, two innovative boom energy saving systems are brought forward. Firstly the principle of the system and the advantage compared with traditional hydraulic boom system are presented. Then through theoretical analysis, the method of energy saving and the sourse of the saved energy are described. Finally, comprehensive comparison between the two energy saving systems is maked and direct use system is selected as the main research object.The design procedures and method for the innovative energy saving system are presented systematically based on the above study. According to the analyses of the design object, the corresponding control strategy is developed, and the components are parameter matched. Then a hydraulic energy saving system for 7-ton excavator is designed using these rules. And the designed system is simulated in the built model under a constant mass load. The simulation results show this system works well.Due to the load of the boom system varies frequently and at large amplitude, mechanical model of work set is constructed, then the hydraulic system of excavator is proportionally reconstructed and adopted PID controller to accurately control the motion of each work component. Then the energy saving system is applied to the proportional excavator. After the simulation research of three operating mode (boom fast down, typical work cycle without and with load), the result shows the innovate energy saving system runs well and has good energy saving effect.Energy saving system experiment is carried out to test and investigate the energy saving effect and controllability, vertify the working principle. On the basis of the experitment result, the energy saving system is revised. During the accelerating period of boom down, restriction control is adopted. And then system is controlled by adjusting the variable disaplacement pump of the energy saving system.
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