Study On Flow Matching Of Hydraulic Impact Mechanism Without Accumulator

Hydraulic impact machinery is a kind of construction machinery whose kinetic energyis from hydraulic and is used to crash rocks. With the expansion of country’s infrastructure,impact machinery such as hydraulic breaker and rock drill is applied more widely.Hydraulic impact mechanism is the common core part of these high speed and powermachinerys. Facing with oil shortage wordwide, construction machinery will developtowards energy saving and environmental protection. At present, most impact machinerysare mounted on excavators and supplied with oil by the pump which driven originallybucket cylinder. This way ignores the characteristics of dramatic changes in speed ofimpact mechanism, thus isn’t the most energy-efficient. For impact mechanism withaccumulators, accumulators play a role of absorbing or releasing oil timely. Relatedliterature shows that impact mechanisms without accumulators can achieve slightly lowerimpact energy than those with accumulators. Plus accumulater is expensive and its lifetimeis short, canceling accumulator becomes a trend. Therefore, an impact mechanism withoutaccumulator is studied, which aims to find out the best match between pump and impactmechanism for maximum impact energy.The work process of impact mechanism is divided into five stages. After deep analysisof work principle, kinetic equations of piston, Nitrogen chamber and directional valvespool, and flow balance equation are established. Simplified models are solved in Matlaband the trends of piston velocity and required flow rate are obtained.Based on non-linear mathematical model of impact machinery and combined withPower Bond Graph points, simulation models of cylinder-body, Nitrogen chamber,directional valve and variable pump are established in the software AMESim. Then acomplete model is combined according to the actual physical structure. With the trueparameters from drawings set into the model, the simulation is carried out. Performance curves under conditions of variable flow rate, constant flow pump, constant pressure pumpand constant power pump are obtained. Through comparative analysis of curves, theconclusion that constant pressure pump is the best oil supply way and that impact energygrows as flow rate increases is obtained.In order to get the data of impact energy and impact frequency, a performance testsystem is designed based on Virtual Instrument Technology. The software for test system isprogrammed in LabVIEW and hardware consists of sensors, NI acquisition card etc. Thesystem is applied into the performance test under different flow rates, showing the curvesof pressure, flow rate, velocity of piston, impact energy and impact frequency. Throughcomparative analysis of those curves, the conclusion got from simulation is proved.The research can provide guidance for selecting pump for existing impactmechanisms and designing energy efficient ones.