| Electro-hydraulic controlled system can be classified into two kinds: valve controlled and pump controlled. Valve controlled system seems to have the advantages of fast response, high control accuracy as well as the ability of controlling multiple actuators with only one source, but problem is that the energy efficiency is very low due to throttling loss. Therefore, valve controlled system suffers huge challenges in many occasions. However, compared with valve controlled system, pump controlled system not only can reduce installed power and generated heat greatly owing to no throttling loss, but also owns the advantage of integration of driving and kinetic-potential recovery, and has become the development direction of electro-hydraulic controlled technology. Although the technology of pump controlled single rod cylinders has made great progress after 20 years of development, there is still having no perfect solutions for compensating the asymmetrical flow of a single rod cylinder. In especial, for the system with frequent reversing in load force direction, such as the excavator arm cylinder, there are always existing speed and pressure oscillations resulting in poor stability of the system, which limits the practical application. Therefore, it is significant to study a kind of stable, reliable and able to match the asymmetrical flow of a single rod cylinder, which has important theoretical significance.According to the domestic and foreign literature, from the aspect of control principle and control strategy of pump direct controlled single rod cylinders, this paper analyzed the research status of pump direct controlled single rod cylinders and researched the advantages and disadvantages of the various control loops. Further, a new system of an asymmetric piston pump direct controlled single rod cylinders is proposed. The main research contents are as follows.First of all, in order to verify operating characteristics of the asymmetrical piston pump, the simulation model is established according to the pump structure and working principle. And its pressure-flow characteristics are simulated analysis and tested by prototype testing. Further, direct controlled hydraulic excavator cylinders which can recover kinetic-potential energy is put forward. When the load force is reversed, there is no mutation of the cylinder velocity. Besides, because of having no throttling loss and overflow loss, the system efficiency is very high. Secondly, based on the working principle of asymmetric pump direct controlled system, the system mathematical model and co-simulation model in software SimulationX are established. Through theoretical analysis, simulation research and experiment of the new system under constant load conditions, the comprehensive evaluation of the system operation and control characteristics is received. The results showed that the system has good control characteristics. Finally, according to the structure parameters of excavator and arm motion law, the virtual prototype of excavator is built in software Pro/E and imported to SimulationX forming to the system of the asymmetric pump direct controlled hydraulic excavator cylinder. At the same time, the simulation is conducted and using the accumulator for energy recovery is proposed.The study demonstrates that, compared with traditional pump controlled system, the new system has good control characteristics under the condition of constant load and variable load. When the load force is reversed, there is no mutation of the cylinder velocity. Just by changing the rotating direction of the servo motor, the single rod hydraulic cylinder can obtain a symmetrical extension and retraction speed, which greatly simplifies the system control strategy, and the energy consumption of the system is also very significantly reduced. |
