Study Of The Load Sensing System With A Long Pipe

This dissertation is derived from the project of the National Science Foundation of China "Research on Electro-Hydraulic Control Theory and Engineering Realization for Construction Machinery with Long Hydraulic Pipeline" and the load sensing system is considered as the main subject investigated. Flow characteristics of oil in long pipes, pipe effects in load sensing system and valve control system and electro-hydraulic load sensing system based on both electrical feedback and fluid pipe feedback have been studied deeply and systematically.In chapter 1, the following items are overviewed firstly. Researches of fluid line dynamics; structure and control method of load sensing multiple unit valve; composition and principle of load sensing system and distribution of pipes in it; present state of study on pipe effects in electro-hydraulic system; development of technique of fluid power system simulation and how pipes are treated in simulation. Based on these overviews, the significance and aims of this dissertation are presented.In chapter 2, the present distribution parameter models of fluid pipe are analysed and compared with each other in both time domain and frequency domain. One of them is considered to be most suitable for theoretical analysis of hydraulic system. Especially, two of suggestions are put forward to improve the traditional lumped parameter model of pipe. The improved model is verified by experiment results.In chapter 3, The mathematical models of load sensing variable displacement pump, load sensing multiple unit valve, pipes, actuator and load are established separately in time domain and frequency domain. Based on these models of components, the analysis model in frequency domain and simulation model in time domain of load sensing system with long pipes are established. When the parameters of components and system meet a certain condition, the models of load sensing system are simplified.In chapter 4, The influences of pipes and adjustable parameter of load sensing variable displacement on load sensing system are investigated by experiments. Some of initial knowledge is obtain from these experimental results. There are mainly two problems caused by long pipes in load sensing system. One is the stability of load sensing variable displacement pump and another is the response lag of feedback pipe. These problems determined the aims of theoretical study.In chapter 5, the two problems caused by long pipes in load sensing system are analyzed deeply by theoretical and simulation method. A theory of optimum design for feedback line and a stability criterion for load sensing variable displacement pump are put forward. As a result, the disadvantage influences of long pipes on load sensing system are limited at utmost. Otherwise, the dynamic behaviors of load sensing system with long pipes are simulated and the simulation results are consistence with experimental results basically, which proves that the mathematical models established in chapter 3 are correct.In chapter 6, A scheme of electro-hydraulic load sensing system is put forward, which is based on both electrical feedback and fluid pipe feedback. The load signals from remote actuators are converted to electrical signals in order to be transmitted rapidly and the load signals from short distance actuators still employ fluid pipes, which are more simple and reliably. The electrical signals from remote actuators are firstly processed by a "feedback signal conditioner" and then are...