The Research On Dynamic Characteristics Of A Hydraulic Lifting System Of Large Crawler Crane

A lifting system is one of the most important systems of a crawler crane. The dynamic performance of the hydraulic lifting system is very important to its stability and security of the cranes. The improving of performance of a hydraulic lifting system is very necessary to the design process of the crawler crane. The crane lifting system runs a motor over-speed phenomenon while the motion of a whole system and the loading effect is in the same direction. Therefore, key technology of the lifting system is the way to ensure the system works with smoothly, efficiently and accurately.The hydraulic lifting systems can be divided into an open and closed form based on the different ways of the fluid cycle. Both systems pressure impact for the dynamic performances are quite different. Therefore, to ensure high performance, it is better to focus on the dynamic characteristics of the hydraulic system despite of the form used. For example, make the system more rational and efficient; a reasonable match between the system parameters; and the optimization of the hydraulic system should be done. However, the domestic research work with the dynamic of the hydraulic lifting system is still in its infancy. Most of the designers have been only focusing on the static parameters of the hydraulic systems and the selections with the hydraulic components are still based on empirical or analog method.This dissertation is funded by the project of "The development of the design and management platform for hydraulic systems in cranes". The research was based on AMESim platform while the testing and simulations of the hydraulic lifting system was carried. Both of the transfer function and HCD model of the hydraulic system are developed for the research on parameters which may have influences on stability of the system. Furthermore, the causes of pressure pulsation of the lifting system are described by means of dynamic simulation and testing.Hence, main research findings of this project can be summarized as following;1. The hydraulic lifting systems, an open and closed, were introduced while discussing of its main components. Mainly, the concept of pressure pulsation of the lifting system for the dynamic performance of a crane hydraulic lifting system was described. 2. The analysis on the transfer function of the counterbalance valve indicated that the stability of the system can be greatly improved with several changes:the decrease of the diameter of the inlet damping; the increase of the spring stiffness; the decrease of the control area of the pilot piston; and the flow area of the control vales with linear form. The analysis on the transfer function of the variable displacement motor indicated that lots of parameters:the initial displacement; the system pressure; and the volume of hydraulic capacity will have impacts on system stability. When the displacement of the motor was set as the minimum one the system works in the worst condition for the stability of the system was really bad. The stability domain of the system could be extended with the increase with the product of the minimum displacement and the system pressure.3. The HCD model of the large crane lifting system developed in the AMESim environment. The causes of pressure pulsation of the lifting system were described by means of dynamic simulation and experimental research. Furthermore, this paper focused on the analysis of the relationship between stability of the lifting system and parameters of the key hydraulic components by the using of dynamic simulation. Several factors were taken into consider such as the flow area form of counterbalance valve; the diameter of inlet orifices; and the variable displacement control mechanism. The analysis result indicated that the pressure pulsation of the lifting system was closely related to dynamic characteristic of the counterbalance valve and cutoff valve, and stability of the system can be improved by means of the flow area of counterbalance valve with linear small gradient.4. The hydraulic lifting system will be influenced by all sorts of disturbances because of the complex operating mode and the bad working conditions therefore optimization solutions are designed to guarantee the system's security, reliability, and efficiency under the complex working conditions. In order to prove the feasibility of the optimization solutions, simulations in a variety of conditions were done.5. Experiments were carried out aimed to study the dynamic performances of the hydraulic lifting system. The dynamic responses of system's pressure and stability of the system were tested with different inlet orifices of the counterbalance valve. The simulation and analysis results about the pressure pulsation were validated by the experiment. Experiments for system's responses with different cutoff pressure values and displacement of motor were carried out respectively. The results showed that both of the small displacement of the motor and the small fluid chamber can caused the pressure fluctuation phenomenon which was also proved by the dynamic simulation.6. Experiments with the optimization solutions applied were carried out. The testing results indicated that the dynamic performances of the hydraulic lifting system were greatly improved, at the same time the problem between a higher efficiency and the stability of the system is solved.