Research On The Hydraulic System Of Excavator

Excavator is a kind of important engineering machinery with extensive application range, such as various of engineering in road, water anservancy, building, mineral etc. The rapid development of national economy promotes people's need for excavator and makes progress in hydraulic technology, an important excavator composition. Hydraulic technology provides a technological basic for modern excavator and decides their performance. A lot of advanced technology is used in excavator, and so research on excavator's hydraulic system is of a great significance. The paper is divided into six chapters. Chapter 1, as introduction, first introduces the development history of excavator and hydraulic technology, and makes a research contrast at home and abroad, finally gives the development trend and research frame of excavator. Chapter 2 discusses excavator's hydraulic system generally. Excavator's hydraulic system is divided into three basic parts according to each function: job device system, slew device system and walk device system. Excavator's hydraulic system has many basic circuits due to its complex action, variable load, frequent vibration and pound and any circuit can complete the particular function. The chapter introduces some circuits such as press limitation and cushion, flow orifice, velocity limitation, confluence, and regeneration, flow lock. Chapter 3 discusses two hydraulic systems applied extensively: open center six way valve system and close center load sensing and press compensation system. The former is generally used in domestic excavator due to low price and the latter is used in abroad excavator. The flow adjust in the former adopts a combined orifice between entrance and bypass and so the performance in flow adjust is affected by load press and pump's flow. When a pump supplies many executors, Hydraulic pump has priority satisfy light load circuit. The flow adjusts in the latter use components of load sensing and press compensator and so the performance in flow adjust is better. The compensator are placed the position between pump and valve (front of valve), between valve and executor (rear of valve) or between executor and circuit to tank. Chapter 3 also discusses the control system of excavator. Excavator's control system is divided into four parts: engine, pump, valve, executor and overall machine control system. Engine control system lays emphasis on electronic, power-optimizing, electronic velometer, and automatic velocity –reducing control. Pump control system puts emphasis on adjust on press, flow and power by variable machine and it is divided into summation power control, distribute power control, cross power control, positive flow control, negative flow control, load sensing control, load limiting control, variable power control and kinds of combination control. Overall machine control on excavator gives emphasis to hydraulic oil temperature control, run control and malfunction finding system, automatic dig control, and remote excavator control system. Chapter 4 takes example for WY20 excavator designed by Xuzhou construction machinery institute and expatiates on its characteristic in hydraulic system. WY20 excavator has a double pump with constant power and cross negative flow control, which can enhance efficiency of hydraulic pump. WY20 excavator has an open center valve with press cushion, walk in a beeline, slew priority and flow lock. Chapter 4 also makes a match calculation of WY20 excavator. First the displacement, drive torque and input power of hydraulic pump and input torque of engine are made certain and then the flexible time of boom, arm and bucket is calculated in the condition of maximum displacement of hydraulic pump, finally the stress intensity and cylinder stability is calculated in the condition of maximum pressure. The result of the calculation is satisfied. Chapter 5 is a verifying experiment. When the load increases, the hydraulic control system automatically regulates the displacement of the pump to match up the engine and vice versa. We get the following conclusion through the experiment: change in swashplate angle or the displacement of the pump makes change finally. Hydraulic pump can make the best of engine power due to change rotary speed of engine following the change in load.Chapter 6 makes a conclusion of the paper: 1)Hydraulic system of excavator needs high efficiency and reliability due to complex work condition. 2)Hydraulic system of excavator has two circuits: one is open center system with low price; the other is close center system with load sensing and pressure compensating. 3)The aim of hydraulic system is combination in the technology of machinery, hydraulic and electronics. The research concentrates on hydraulic control system of excavator. 4)WY20 excavator designed by Xuzhou construction machinery institute in 1990's is a representative of advanced excavator with energy –saving and high efficiency.