Design And Research On The Auxiliary Oil-Absorption Device Of Hydraulic PUMP Based On The Jet-Flow Principle

As the power supply unit of hydraulic system, pump is very important for the system. In practical applications, because of unreasonable design or special needs of the structure and properties, suction resistance of pump will be great or pump will suck air directly, which lead to insufficient oil-absorption of hydraulic pump. This phenomenon will cause a series of problems, such as cavitation, pressure and flow pulsation, vibration, noise, etc. With hydraulic technology develops towards the trend of high-pressure, high-speed, high-power, this phenomenon becomes increasingly evident. To solve this problem, the project team has proposed an auxiliary oil-absorption technology based on jet-flow principle, and done some related simulation and experiment. The results show this technique is feasible, but the device’s effect of the preliminary design needs to be improved.After summarizing the preparatory work, combining fluid mechanics, jet-flow principle and other related knowledge, and referring to the structure of the jet pump, two types of auxiliary devices were proposed(center device and annular device).By CFD software, the devices were designed and verified in detail. The main work is as follows:(1)With taking efficiency as the evaluation criteria of device’s performance, the efficiency characteristics of the devices and the main parameters affecting the efficiency (including working conditions, structure parameters and physical properties of the oil etc) are researched in detail by CFD software, then we can draw general law that can provide reference for design of auxiliary devices. Study found that, under the condition that work flow is constant, with the sucked flow rate changing, there is a optimum entrainment ratio corresponding to the maximum efficiency. Other structural parameters in addition to the area ratio will affect the efficiency value, but little effect on the optimum entrainment ratio. Different area ratio and viscosity have different optimum entrainment ratio, so it must ensure a reasonable match between the three, in order to ensure high efficiency of the device.(2)Simulating cavitation phenomena within the devices, comparing their differences and similarities of two different devices, then the reason of different cavitations is explained. Research found that cavitation will generate bubbles, which results in choking of the flow within throat and the sucked flow rate no longer increasing, so the efficiency of the device declines. The most effective way to avoid cavitation in the devices is appropriate to increase the diameter of the throat.(3)A CFD model of axial piston pump is established first, by analyzing flow characteristics of the piston pump found that, the phenomena of oil back flushing during absorption process will generate high speed jet, and it causes localized low pressure in the plunger hole and is prone to generate cavitation, so the elastic modulus decreased rapidly and the pressure in plunger hole rises slower, which results in big flow pulsation in piston pump. Inlet pressure, system pressure, gas content in the oil and speed of the pump will affect the cavitation during back flush stage, thus affecting absorption process.(4)A CFD model of device connected to the hydraulic pump is established, then its auxiliary performance is validated and the auxiliary oil-absorption principle gets explained. Comparing the performance of devices with different structure under different work conditions, then the working characteristics of different devices is obtained. Finally combining with all of the previous conclusions, the design method of auxiliary device is summarized.