Study On Charge Pump Of Closed Hydraulic System

Now closed hydraulic system has become one of trends of development. It has lots of advantage,for example, compact structure, high efficiency, stable transmission without throttling and overflow loss. Closed hydraulic system adopts two-way variable displacement pump. Usually the oil from the pump inflood the motor directly.Reversing the angle of the swashplate reverses the flow of oil from the pump and thus reverses the direction of rotation of the motor output.In the closed hydraulic system, the charge pump provides flow to make up internal leakage, maintain a positive pressure in the main circuit, provide flow for cooling and filtration, replace any leakage losses from external valving or auxiliary systems, and to provide flow and pressure for the control system. If the displacement of the charge pump is smaller than needed, the system can not work normally. On the other hand, the larger displacement charge pump will bring the unnecessary power loss to the system. Therefore the reasonable selection for charge pump counts for much.The article chooses the series 90 pump and motor made by the company of Sauer Danfoss in America to analysis. The flow of the charge pump is divided into four parts:the leakage flow of the pump and motor, the flow for control system, the flow of loop flushing valve and the flow of charge pressure relief valve. According to the work points of the system, calculating the minimum flow that the charge pump provides, discuss the influence to the work points by the different charge pumps.The results show the leakage will exceed the flow that the charge pump is capable of providing at low input speeds and high pressures;the temperature of the oil will be exorbitant at high input speeds and high pressures. The choose of the radiator and tanks in the closed hydraulic system relates to the paramete of charge pump. calculate the volume of tanks and the area of radiators when the system uses different displacement charge pump.The volume efficiency of the hydraulic system will drop beacause after long-term used the hydraulic system will wear and tear. It causes that the leakage flow and heating power increase, so the design of the charge pump should set some allowance. Choose the work points with the hydraulic system, calculate the leakage flow and heating power when the volume efficiency of the system drops. And analyse if the flow of the charge pump is enough and the oil temperature is overrun. The results show that volume efficiency when the flow of the charge pump is not enough is higher than the volume efficiency when the oil temperature is overrun.Analyse and calculate the additional charge pump flow required in the conditions of high impact load or long pipe.